gas: generate .sframe from CFI directives

Currently supported for x86_64 and aarch64 only.

[PS: Currently, the compiler has not been adapted to generate
".cfi_sections" with ".sframe" in it.  The newly added command line
option of --gsframe provides an easy way to try out .sframe support
in the toolchain.]

gas interprets the CFI directives to generate DWARF-based .eh_frame
info.  These internal DWARF structures are now consumed by
gen-sframe.[ch] sub-system to, in turn, create the SFrame unwind
information.  These internal DWARF structures are read-only for the
purpose of SFrame unwind info generation.

SFrame unwind info generation does not impact .eh_frame unwind info
generation.  Both .eh_frame and .sframe can co-exist in an ELF file,
if so desired by the user.

Recall that SFrame unwind information only contains the minimal
necessary information to generate backtraces and does not provide
information to recover all callee-saved registers.  The reason being
that callee-saved registers other than FP are not needed for stack
unwinding, and hence are not included in the .sframe section.

Consequently, gen-sframe.[ch] only needs to interpret a subset of
DWARF opcodes in gas.  More details follow.

[Set 1, Interpreted] The following opcodes are interpreted:
- DW_CFA_advance_loc
- DW_CFA_def_cfa
- DW_CFA_def_cfa_register
- DW_CFA_def_cfa_offset
- DW_CFA_offset
- DW_CFA_remember_state
- DW_CFA_restore_state
- DW_CFA_restore

[Set 2, Bypassed] The following opcodes are acknowledged but are not
necessary for generating SFrame unwind info:
- DW_CFA_undefined
- DW_CFA_same_value

Anything else apart from the two above-mentioned sets is skipped
altogether.  This means that any function containing a CFI directive not
in Set 1 or Set 2 above, will not have any SFrame unwind information
generated for them.  Holes in instructions covered by FREs of a single
FDE are not representable in the SFrame unwind format.

As few examples, following opcodes are not processed for .sframe
generation, and are skipped:
- .cfi_personality*
- .cfi_*lsda
- .cfi_escape
- .cfi_negate_ra_state
- ...

Not processing .cfi_escape, .cfi_negate_ra_state will cause SFrame
unwind information to be absent for SFrame FDEs that contain these CFI
directives, hence affecting the asynchronicity.

x86-64 and aarch64 backends need to have a few new definitions and
functions for .sframe generation.  These provide gas with architecture
specific information like the SP/FP/RA register numbers and an
SFrame-specific ABI marker.

Lastly, the patch also implements an optimization for size, where
specific fragments containing SFrame FRE start address and SFrame FDE
function are fixed up.  This is similar to other similar optimizations
in gas, where fragments are sized and fixed up when the associated
symbols can be resolved.  This optimization is controlled by a #define
SFRAME_FRE_TYPE_SELECTION_OPT and should be easy to turn off if needed.
The optimization is on by default for both x86_64 and aarch64.

ChangeLog:

	* gas/Makefile.am: Include gen-sframe.c and sframe-opt.c.
	* gas/Makefile.in: Regenerated.
	* gas/as.h (enum _relax_state): Add new state rs_sframe.
	(sframe_estimate_size_before_relax): New function.
	(sframe_relax_frag): Likewise.
	(sframe_convert_frag): Likewise.
	* gas/config/tc-aarch64.c (aarch64_support_sframe_p): New
	definition.
	(aarch64_sframe_ra_tracking_p): Likewise.
	(aarch64_sframe_cfa_ra_offset): Likewise.
	(aarch64_sframe_get_abi_arch): Likewise.
	(md_begin): Set values of sp/fp/ra registers.
	* gas/config/tc-aarch64.h (aarch64_support_sframe_p): New
	declaration.
	(support_sframe_p): Likewise.
	(SFRAME_CFA_SP_REG): Likewise.
	(SFRAME_CFA_FP_REG): Likewise.
	(SFRAME_CFA_RA_REG): Likewise.
	(aarch64_sframe_ra_tracking_p): Likewise.
	(sframe_ra_tracking_p): Likewise.
	(aarch64_sframe_cfa_ra_offset): Likewise.
	(sframe_cfa_ra_offset): Likewise.
	(aarch64_sframe_get_abi_arch): Likewise.
	(sframe_get_abi_arch): Likewise.
	* gas/config/tc-i386.c (x86_support_sframe_p): New definition.
	(x86_sframe_ra_tracking_p): Likewise.
	(x86_sframe_cfa_ra_offset): Likewise.
	(x86_sframe_get_abi_arch): Likewise.
	* gas/config/tc-i386.h (x86_support_sframe_p): New declaration.
	(support_sframe_p): Likewise.
	(SFRAME_CFA_SP_REG): Likewise.
	(SFRAME_CFA_FP_REG): Likewise.
	(x86_sframe_ra_tracking_p): Likewise.
	(sframe_ra_tracking_p): Likewise.
	(x86_sframe_cfa_ra_offset): Likewise.
	(sframe_cfa_ra_offset): Likewise.
	(x86_sframe_get_abi_arch): Likewise.
	(sframe_get_abi_arch): Likewise.
	* gas/config/tc-xtensa.c (unrelaxed_frag_max_size): Add case for
	rs_sframe.
	* gas/doc/as.texi: Add .sframe to the documentation for
	.cfi_sections.
	* gas/dw2gencfi.c (cfi_finish): Create a .sframe section.
	* gas/dw2gencfi.h (CFI_EMIT_sframe): New definition.
	* gas/write.c (cvt_frag_to_fill): Handle rs_sframe.
	(relax_segment): Likewise.
	* gas/gen-sframe.c: New file.
	* gas/gen-sframe.h: New file.
	* gas/sframe-opt.c: New file.

15 files changed, 1844 insertions, 10 deletions

diff --git a/gas/Makefile.am b/gas/Makefile.am
index 5f0f24a..4661a718 100644
--- a/gas/Makefile.am
+++ b/gas/Makefile.am
@@ -80,6 +80,7 @@ GAS_CFILES = \
 	flonum-konst.c \
 	flonum-mult.c \
 	frags.c \
+	gen-sframe.c \
 	hash.c \
 	input-file.c \
 	input-scrub.c \
@@ -91,6 +92,7 @@ GAS_CFILES = \
 	read.c \
 	remap.c \
 	sb.c \
+	sframe-opt.c \
 	stabs.c \
 	subsegs.c \
 	symbols.c \
@@ -113,6 +115,7 @@ HFILES = \
 	expr.h \
 	flonum.h \
 	frags.h \
+	gen-sframe.h \
 	hash.h \
 	input-file.h \
 	itbl-lex.h \
diff --git a/gas/Makefile.in b/gas/Makefile.in
index 5a4dd70..1e01f34 100644
--- a/gas/Makefile.in
+++ b/gas/Makefile.in
@@ -166,10 +166,11 @@ am__objects_1 = app.$(OBJEXT) as.$(OBJEXT) atof-generic.$(OBJEXT) \
 	dwarf2dbg.$(OBJEXT) dw2gencfi.$(OBJEXT) ecoff.$(OBJEXT) \
 	ehopt.$(OBJEXT) expr.$(OBJEXT) flonum-copy.$(OBJEXT) \
 	flonum-konst.$(OBJEXT) flonum-mult.$(OBJEXT) frags.$(OBJEXT) \
-	hash.$(OBJEXT) input-file.$(OBJEXT) input-scrub.$(OBJEXT) \
-	listing.$(OBJEXT) literal.$(OBJEXT) macro.$(OBJEXT) \
-	messages.$(OBJEXT) output-file.$(OBJEXT) read.$(OBJEXT) \
-	remap.$(OBJEXT) sb.$(OBJEXT) stabs.$(OBJEXT) subsegs.$(OBJEXT) \
+	gen-sframe.$(OBJEXT) hash.$(OBJEXT) input-file.$(OBJEXT) \
+	input-scrub.$(OBJEXT) listing.$(OBJEXT) literal.$(OBJEXT) \
+	macro.$(OBJEXT) messages.$(OBJEXT) output-file.$(OBJEXT) \
+	read.$(OBJEXT) remap.$(OBJEXT) sb.$(OBJEXT) \
+	sframe-opt.$(OBJEXT) stabs.$(OBJEXT) subsegs.$(OBJEXT) \
 	symbols.$(OBJEXT) write.$(OBJEXT)
 am_as_new_OBJECTS = $(am__objects_1)
 am__dirstamp = $(am__leading_dot)dirstamp
@@ -566,6 +567,7 @@ GAS_CFILES = \
 	flonum-konst.c \
 	flonum-mult.c \
 	frags.c \
+	gen-sframe.c \
 	hash.c \
 	input-file.c \
 	input-scrub.c \
@@ -577,6 +579,7 @@ GAS_CFILES = \
 	read.c \
 	remap.c \
 	sb.c \
+	sframe-opt.c \
 	stabs.c \
 	subsegs.c \
 	symbols.c \
@@ -598,6 +601,7 @@ HFILES = \
 	expr.h \
 	flonum.h \
 	frags.h \
+	gen-sframe.h \
 	hash.h \
 	input-file.h \
 	itbl-lex.h \
@@ -1302,6 +1306,7 @@ distclean-compile:
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/flonum-konst.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/flonum-mult.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/frags.Po@am__quote@
+@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/gen-sframe.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/hash.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/input-file.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/input-scrub.Po@am__quote@
@@ -1316,6 +1321,7 @@ distclean-compile:
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/read.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/remap.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/sb.Po@am__quote@
+@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/sframe-opt.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/stabs.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/subsegs.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/symbols.Po@am__quote@
diff --git a/gas/as.h b/gas/as.h
index 1b92407..23542e4 100644
--- a/gas/as.h
+++ b/gas/as.h
@@ -261,7 +261,10 @@ enum _relax_state
   rs_cfa,
 
   /* Cross-fragment dwarf2 line number optimization.  */
-  rs_dwarf2dbg
+  rs_dwarf2dbg,
+
+  /* SFrame FRE type selection optimization.  */
+  rs_sframe
 };
 
 typedef enum _relax_state relax_stateT;
@@ -528,6 +531,11 @@ int eh_frame_relax_frag (fragS *);
 void eh_frame_convert_frag (fragS *);
 int generic_force_reloc (struct fix *);
 
+/* SFrame FRE optimization.  */
+int sframe_estimate_size_before_relax (fragS *);
+int sframe_relax_frag (fragS *);
+void sframe_convert_frag (fragS *);
+
 #include "expr.h"		/* Before targ-*.h */
 
 /* This one starts the chain of target dependent headers.  */
diff --git a/gas/config/tc-aarch64.c b/gas/config/tc-aarch64.c
index 165d927..c679d93 100644
--- a/gas/config/tc-aarch64.c
+++ b/gas/config/tc-aarch64.c
@@ -30,6 +30,9 @@
 
 #ifdef OBJ_ELF
 #include "elf/aarch64.h"
+#include "dw2gencfi.h"
+#include "sframe.h"
+#include "gen-sframe.h"
 #endif
 
 #include "dw2gencfi.h"
@@ -72,6 +75,11 @@ enum aarch64_abi_type
   AARCH64_ABI_LLP64 = 3
 };
 
+unsigned int aarch64_sframe_cfa_sp_reg;
+/* The other CFA base register for SFrame unwind info.  */
+unsigned int aarch64_sframe_cfa_fp_reg;
+unsigned int aarch64_sframe_cfa_ra_reg;
+
 #ifndef DEFAULT_ARCH
 #define DEFAULT_ARCH "aarch64"
 #endif
@@ -8403,6 +8411,50 @@ aarch64_init_frag (fragS * fragP, int max_chars)
       break;
     }
 }
+
+/* Whether SFrame unwind info is supported.  */
+
+bool
+aarch64_support_sframe_p (void)
+{
+  /* At this time, SFrame is supported for aarch64 only.  */
+  return (aarch64_abi == AARCH64_ABI_LP64);
+}
+
+/* Specify if RA tracking is needed.  */
+
+bool
+aarch64_sframe_ra_tracking_p (void)
+{
+  return true;
+}
+
+/* Specify the fixed offset to recover RA from CFA.
+   (useful only when RA tracking is not needed).  */
+
+offsetT
+aarch64_sframe_cfa_ra_offset (void)
+{
+  return (offsetT) SFRAME_CFA_FIXED_RA_INVALID;
+}
+
+/* Get the abi/arch indentifier for SFrame.  */
+
+unsigned char
+aarch64_sframe_get_abi_arch (void)
+{
+  unsigned char sframe_abi_arch = 0;
+
+  if (aarch64_support_sframe_p ())
+    {
+      sframe_abi_arch = target_big_endian
+	? SFRAME_ABI_AARCH64_ENDIAN_BIG
+	: SFRAME_ABI_AARCH64_ENDIAN_LITTLE;
+    }
+
+  return sframe_abi_arch;
+}
+
 #endif /* OBJ_ELF */
 
 /* Initialize the DWARF-2 unwind information for this procedure.  */
@@ -9688,6 +9740,12 @@ md_begin (void)
     mach = bfd_mach_aarch64;
 
   bfd_set_arch_mach (stdoutput, TARGET_ARCH, mach);
+#ifdef OBJ_ELF
+  /* FIXME - is there a better way to do it ?  */
+  aarch64_sframe_cfa_sp_reg = 31;
+  aarch64_sframe_cfa_fp_reg = 29; /* x29.  */
+  aarch64_sframe_cfa_ra_reg = 30;
+#endif
 }
 
 /* Command line processing.  */
diff --git a/gas/config/tc-aarch64.h b/gas/config/tc-aarch64.h
index 2d514ff..91412ce 100644
--- a/gas/config/tc-aarch64.h
+++ b/gas/config/tc-aarch64.h
@@ -239,6 +239,35 @@ struct aarch64_segment_info_type
 /* We want .cfi_* pseudo-ops for generating unwind info.  */
 #define TARGET_USE_CFIPOP              1
 
+/* Whether SFrame unwind info is supported.  */
+extern bool aarch64_support_sframe_p (void);
+#define support_sframe_p aarch64_support_sframe_p
+
+/* The stack-pointer register number for SFrame unwind info.  */
+extern unsigned int aarch64_sframe_cfa_sp_reg;
+#define SFRAME_CFA_SP_REG aarch64_sframe_cfa_sp_reg
+
+/* The base-pointer register number for CFA unwind info.  */
+extern unsigned int aarch64_sframe_cfa_fp_reg;
+#define SFRAME_CFA_FP_REG aarch64_sframe_cfa_fp_reg
+
+/* The return address register number for CFA unwind info.  */
+extern unsigned int aarch64_sframe_cfa_ra_reg;
+#define SFRAME_CFA_RA_REG aarch64_sframe_cfa_ra_reg
+
+/* Specify if RA tracking is needed.  */
+extern bool aarch64_sframe_ra_tracking_p (void);
+#define sframe_ra_tracking_p aarch64_sframe_ra_tracking_p
+
+/* Specify the fixed offset to recover RA from CFA.
+   (useful only when RA tracking is not needed).  */
+extern offsetT aarch64_sframe_cfa_ra_offset (void);
+#define sframe_cfa_ra_offset aarch64_sframe_cfa_ra_offset
+
+/* The abi/arch indentifier for SFrame.  */
+unsigned char aarch64_sframe_get_abi_arch (void);
+#define sframe_get_abi_arch aarch64_sframe_get_abi_arch
+
 /* CFI hooks.  */
 #define tc_regname_to_dw2regnum            tc_aarch64_regname_to_dw2regnum
 #define tc_cfi_frame_initial_instructions  tc_aarch64_frame_initial_instructions
diff --git a/gas/config/tc-i386.c b/gas/config/tc-i386.c
index a5ea9b1..5bc3a56 100644
--- a/gas/config/tc-i386.c
+++ b/gas/config/tc-i386.c
@@ -30,6 +30,8 @@
 #include "subsegs.h"
 #include "dwarf2dbg.h"
 #include "dw2gencfi.h"
+#include "gen-sframe.h"
+#include "sframe.h"
 #include "elf/x86-64.h"
 #include "opcodes/i386-init.h"
 #include <limits.h>
@@ -591,6 +593,12 @@ static int use_big_obj = 0;
 #if defined (OBJ_ELF) || defined (OBJ_MAYBE_ELF)
 /* 1 if generating code for a shared library.  */
 static int shared = 0;
+
+unsigned int x86_sframe_cfa_sp_reg;
+/* The other CFA base register for SFrame unwind info.  */
+unsigned int x86_sframe_cfa_fp_reg;
+unsigned int x86_sframe_cfa_ra_reg;
+
 #endif
 
 /* 1 for intel syntax,
@@ -3099,6 +3107,10 @@ md_begin (void)
       x86_dwarf2_return_column = 16;
 #endif
       x86_cie_data_alignment = -8;
+#if defined (OBJ_ELF) || defined (OBJ_MAYBE_ELF)
+      x86_sframe_cfa_sp_reg = 7;
+      x86_sframe_cfa_fp_reg = 6;
+#endif
     }
   else
     {
@@ -9131,6 +9143,44 @@ x86_cleanup (void)
   if (seg && subseg)
     subseg_set (seg, subseg);
 }
+
+bool
+x86_support_sframe_p (void)
+{
+  /* At this time, SFrame unwind is supported for AMD64 ABI only.  */
+  return (x86_elf_abi == X86_64_ABI);
+}
+
+bool
+x86_sframe_ra_tracking_p (void)
+{
+  /* In AMD64, return address is always stored on the stack at a fixed offset
+     from the CFA (provided via x86_sframe_cfa_ra_offset ()).
+     Do not track explicitly via an SFrame Frame Row Entry.  */
+  return false;
+}
+
+offsetT
+x86_sframe_cfa_ra_offset (void)
+{
+  gas_assert (x86_elf_abi == X86_64_ABI);
+  return (offsetT) -8;
+}
+
+unsigned char
+x86_sframe_get_abi_arch (void)
+{
+  unsigned char sframe_abi_arch = 0;
+
+  if (x86_support_sframe_p ())
+    {
+      gas_assert (!target_big_endian);
+      sframe_abi_arch = SFRAME_ABI_AMD64_ENDIAN_LITTLE;
+    }
+
+  return sframe_abi_arch;
+}
+
 #endif
 
 static unsigned int
diff --git a/gas/config/tc-i386.h b/gas/config/tc-i386.h
index a6e096e..9003726 100644
--- a/gas/config/tc-i386.h
+++ b/gas/config/tc-i386.h
@@ -362,6 +362,32 @@ extern bfd_vma x86_64_section_letter (int, const char **);
 #if defined (OBJ_ELF) || defined (OBJ_MAYBE_ELF)
 extern void x86_cleanup (void);
 #define md_cleanup() x86_cleanup ()
+
+/* Whether SFrame unwind info is supported.  */
+extern bool x86_support_sframe_p (void);
+#define support_sframe_p x86_support_sframe_p
+
+/* The stack-pointer register number for SFrame unwind info.  */
+extern unsigned int x86_sframe_cfa_sp_reg;
+#define SFRAME_CFA_SP_REG x86_sframe_cfa_sp_reg
+
+/* The frame-pointer register number for CFA unwind info.  */
+extern unsigned int x86_sframe_cfa_fp_reg;
+#define SFRAME_CFA_FP_REG x86_sframe_cfa_fp_reg
+
+/* Specify if RA tracking is needed.  */
+extern bool x86_sframe_ra_tracking_p (void);
+#define sframe_ra_tracking_p x86_sframe_ra_tracking_p
+
+/* Specify the fixed offset to recover RA from CFA.
+   (useful only when RA tracking is not needed).  */
+extern offsetT x86_sframe_cfa_ra_offset (void);
+#define sframe_cfa_ra_offset x86_sframe_cfa_ra_offset
+
+/* The abi/arch indentifier for SFrame.  */
+extern unsigned char x86_sframe_get_abi_arch (void);
+#define sframe_get_abi_arch x86_sframe_get_abi_arch
+
 #endif
 
 #ifdef TE_PE
diff --git a/gas/config/tc-xtensa.c b/gas/config/tc-xtensa.c
index b7403ac..f7a28d3 100644
--- a/gas/config/tc-xtensa.c
+++ b/gas/config/tc-xtensa.c
@@ -8616,6 +8616,7 @@ unrelaxed_frag_max_size (fragS *fragP)
     case rs_leb128:
     case rs_cfa:
     case rs_dwarf2dbg:
+    case rs_sframe:
       /* No further adjustments needed.  */
       break;
     case rs_machine_dependent:
diff --git a/gas/doc/as.texi b/gas/doc/as.texi
index 83f49c5..32300d7 100644
--- a/gas/doc/as.texi
+++ b/gas/doc/as.texi
@@ -4883,11 +4883,15 @@ Each expression is assembled into the next byte.
 @subsection @code{.cfi_sections @var{section_list}}
 @cindex @code{cfi_sections} directive
 @code{.cfi_sections} may be used to specify whether CFI directives
-should emit @code{.eh_frame} section and/or @code{.debug_frame} section.
-If @var{section_list} is @code{.eh_frame}, @code{.eh_frame} is emitted,
-if @var{section_list} is @code{.debug_frame}, @code{.debug_frame} is emitted.
-To emit both use @code{.eh_frame, .debug_frame}.  The default if this
-directive is not used is @code{.cfi_sections .eh_frame}.
+should emit @code{.eh_frame} section, @code{.debug_frame} section and/or
+@code{.sframe} section.  If @var{section_list} contains @code{.eh_frame},
+@code{.eh_frame} is emitted, if @var{section_list} contains
+@code{.debug_frame}, @code{.debug_frame} is emitted, and finally, if
+@var{section_list} contains @code{.sframe}, @code{.sframe} is emitted.
+To emit multiple sections, specify them together in a list.  For example, to
+emit both @code{.eh_frame} and @code{.debug_frame}, use
+@code{.eh_frame, .debug_frame}.  The default if this directive is not used
+is @code{.cfi_sections .eh_frame}.
 
 On targets that support compact unwinding tables these can be generated
 by specifying @code{.eh_frame_entry} instead of @code{.eh_frame}.
diff --git a/gas/dw2gencfi.c b/gas/dw2gencfi.c
index 80b2628..d18cd26 100644
--- a/gas/dw2gencfi.c
+++ b/gas/dw2gencfi.c
@@ -23,6 +23,7 @@
 #include "dw2gencfi.h"
 #include "subsegs.h"
 #include "dwarf2dbg.h"
+#include "gen-sframe.h"
 
 #ifdef TARGET_USE_CFIPOP
 
@@ -102,6 +103,11 @@
 #define tc_cfi_reloc_for_encoding(e) BFD_RELOC_NONE
 #endif
 
+/* Targets which support SFrame format will define this and return true.  */
+#ifndef support_sframe_p
+# define support_sframe_p() false
+#endif
+
 /* Private segment collection list.  */
 struct dwcfi_seg_list
 {
@@ -1235,6 +1241,8 @@ dot_cfi_sections (int ignored ATTRIBUTE_UNUSED)
 	else if (strcmp (name, tc_cfi_section_name) == 0)
 	  sections |= CFI_EMIT_target;
 #endif
+	else if (startswith (name, ".sframe"))
+	    sections |= CFI_EMIT_sframe;
 	else
 	  {
 	    *input_line_pointer = c;
@@ -2495,6 +2503,28 @@ cfi_finish (void)
     }
 
   cfi_sections_set = true;
+  /* Generate SFrame section if the user specifies:
+	- the command line option to gas, or
+	- .sframe in the .cfi_sections directive.  */
+  if (flag_gen_sframe || (all_cfi_sections & CFI_EMIT_sframe) != 0)
+    {
+      if (support_sframe_p ())
+	{
+	  segT sframe_seg;
+	  int alignment = ffs (DWARF2_ADDR_SIZE (stdoutput)) - 1;
+
+	  if (!SUPPORT_FRAME_LINKONCE)
+	    sframe_seg = get_cfi_seg (NULL, ".sframe",
+					 (SEC_ALLOC | SEC_LOAD | SEC_DATA
+					  | DWARF2_EH_FRAME_READ_ONLY),
+					 alignment);
+	  output_sframe (sframe_seg);
+	}
+      else
+	as_bad (_(".sframe not supported for target"));
+    }
+
+  cfi_sections_set = true;
   if ((all_cfi_sections & CFI_EMIT_debug_frame) != 0)
     {
       int alignment = ffs (DWARF2_ADDR_SIZE (stdoutput)) - 1;
diff --git a/gas/dw2gencfi.h b/gas/dw2gencfi.h
index 0f5ae77..4ac70d0 100644
--- a/gas/dw2gencfi.h
+++ b/gas/dw2gencfi.h
@@ -205,5 +205,6 @@ extern struct fde_entry *all_fde_data;
 #define CFI_EMIT_debug_frame            (1 << 1)
 #define CFI_EMIT_target                 (1 << 2)
 #define CFI_EMIT_eh_frame_compact       (1 << 3)
+#define CFI_EMIT_sframe                 (1 << 4)
 
 #endif /* DW2GENCFI_H */
diff --git a/gas/gen-sframe.c b/gas/gen-sframe.c
new file mode 100644
index 0000000..13f5bda
--- /dev/null
+++ b/gas/gen-sframe.c
@@ -0,0 +1,1294 @@
+/* gen-sframe.c - Support for generating SFrame section.
+   Copyright (C) 2022 Free Software Foundation, Inc.
+
+   This file is part of GAS, the GNU Assembler.
+
+   GAS is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3, or (at your option)
+   any later version.
+
+   GAS is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with GAS; see the file COPYING.  If not, write to the Free
+   Software Foundation, 51 Franklin Street - Fifth Floor, Boston, MA
+   02110-1301, USA.  */
+
+#include "as.h"
+#include "subsegs.h"
+#include "sframe.h"
+#include "gen-sframe.h"
+#include "dw2gencfi.h"
+
+#ifdef support_sframe_p
+
+/* By default, use 32-bit relocations from .sframe into .text.  */
+#ifndef SFRAME_RELOC_SIZE
+# define SFRAME_RELOC_SIZE 4
+#endif
+
+/* Whether frame row entries track RA.
+
+   A target may not need return address tracking for stack unwinding.  If it
+   does need the same, SFRAME_CFA_RA_REG must be defined with the return
+   address register number.  */
+
+#if defined (sframe_ra_tracking_p) && defined (SFRAME_CFA_RA_REG)
+# ifndef SFRAME_FRE_RA_TRACKING
+# define SFRAME_FRE_RA_TRACKING 1
+# endif
+#endif
+
+/* SFrame FRE type selection optimization is an optimization for size.
+
+   There are three flavors of SFrame FRE representation in the binary format:
+     - sframe_frame_row_entry_addr1 where the FRE start address is 1 byte.
+     - sframe_frame_row_entry_addr2 where the FRE start address is 2 bytes.
+     - sframe_frame_row_entry_addr4 where the FRE start address is 4 bytes.
+
+   Note that in the SFrame format, all SFrame FREs of a function use one
+   single representation.  The SFrame FRE type itself is identified via the
+   information in the SFrame FDE function info.
+
+   Now, to select the minimum required one from the list above, one needs to
+   make a decision based on the size (in bytes) of the function.
+
+   As a result, for this optimization, some fragments (generated with a new
+   type rs_sframe) for the SFrame section are fixed up later.
+
+   This optimization (for size) is enabled by default.  */
+
+#ifndef SFRAME_FRE_TYPE_SELECTION_OPT
+# define SFRAME_FRE_TYPE_SELECTION_OPT 1
+#endif
+
+/* Emit a single byte into the current segment.  */
+
+static inline void
+out_one (int byte)
+{
+  FRAG_APPEND_1_CHAR (byte);
+}
+
+/* Emit a two-byte word into the current segment.  */
+
+static inline void
+out_two (int data)
+{
+  md_number_to_chars (frag_more (2), data, 2);
+}
+
+/* Emit a four byte word into the current segment.  */
+
+static inline void
+out_four (int data)
+{
+  md_number_to_chars (frag_more (4), data, 4);
+}
+
+/* Get the start address symbol from the DWARF FDE.  */
+
+static symbolS*
+get_dw_fde_start_addrS (const struct fde_entry *dw_fde)
+{
+  return dw_fde->start_address;
+}
+
+/* Get the start address symbol from the DWARF FDE.  */
+
+static symbolS*
+get_dw_fde_end_addrS (const struct fde_entry *dw_fde)
+{
+  return dw_fde->end_address;
+}
+
+/* SFrame Frame Row Entry (FRE) related functions.  */
+
+static void
+sframe_fre_set_begin_addr (struct sframe_row_entry *fre, symbolS *beginS)
+{
+  fre->pc_begin = beginS;
+}
+
+static void
+sframe_fre_set_end_addr (struct sframe_row_entry *fre, symbolS *endS)
+{
+  fre->pc_end = endS;
+}
+
+static void
+sframe_fre_set_cfa_base_reg (struct sframe_row_entry *fre,
+			     unsigned int cfa_base_reg)
+{
+  fre->cfa_base_reg = cfa_base_reg;
+  fre->merge_candidate = false;
+}
+
+static void
+sframe_fre_set_cfa_offset (struct sframe_row_entry *fre,
+			   offsetT cfa_offset)
+{
+  fre->cfa_offset = cfa_offset;
+  fre->merge_candidate = false;
+}
+
+#ifdef SFRAME_FRE_RA_TRACKING
+static void
+sframe_fre_set_ra_track (struct sframe_row_entry *fre, offsetT ra_offset)
+{
+  fre->ra_loc = SFRAME_FRE_ELEM_LOC_STACK;
+  fre->ra_offset = ra_offset;
+  fre->merge_candidate = false;
+}
+#endif
+
+static void
+sframe_fre_set_bp_track (struct sframe_row_entry *fre, offsetT bp_offset)
+{
+  fre->bp_loc = SFRAME_FRE_ELEM_LOC_STACK;
+  fre->bp_offset = bp_offset;
+  fre->merge_candidate = false;
+}
+
+/* All stack offset values within an FRE are uniformly encoded in the same
+   number of bytes.  The size of the stack offset values will, however, vary
+   across FREs.  */
+
+#define VALUE_8BIT  0x7f
+#define VALUE_16BIT 0x7fff
+#define VALUE_32BIT 0x7fffffff
+#define VALUE_64BIT 0x7fffffffffffffff
+
+/* Given a signed offset, return the size in bytes needed to represent it.  */
+
+static unsigned int
+get_offset_size_in_bytes (offsetT value)
+{
+  unsigned int size = 0;
+
+  if (value <= VALUE_8BIT && value >= (offsetT) -VALUE_8BIT)
+    size = 1;
+  else if (value <= VALUE_16BIT && value >= (offsetT) -VALUE_16BIT)
+    size = 2;
+  else if (value <= VALUE_32BIT && value >= (offsetT) -VALUE_32BIT)
+    size = 4;
+  else if ((sizeof (offsetT) > 4) && (value <= (offsetT) VALUE_64BIT
+				      && value >= (offsetT) -VALUE_64BIT))
+    size = 8;
+
+  return size;
+}
+
+#define SFRAME_FRE_OFFSET_FUNC_MAP_INDEX_1B  0 /* SFRAME_FRE_OFFSET_1B.  */
+#define SFRAME_FRE_OFFSET_FUNC_MAP_INDEX_2B  1 /* SFRAME_FRE_OFFSET_2B.  */
+#define SFRAME_FRE_OFFSET_FUNC_MAP_INDEX_4B  2 /* SFRAME_FRE_OFFSET_4B.  */
+#define SFRAME_FRE_OFFSET_FUNC_MAP_INDEX_8B  3 /* Not supported in SFrame.  */
+#define SFRAME_FRE_OFFSET_FUNC_MAP_INDEX_MAX SFRAME_FRE_OFFSET_FUNC_MAP_INDEX_8B
+
+/* Helper struct for mapping offset size to output functions.  */
+
+struct sframe_fre_offset_func_map
+{
+  unsigned int offset_size;
+  void (*out_func)(int);
+};
+
+/* Given an OFFSET_SIZE, return the size in bytes needed to represent it.  */
+
+static unsigned int
+sframe_fre_offset_func_map_index (unsigned int offset_size)
+{
+  unsigned int index = SFRAME_FRE_OFFSET_FUNC_MAP_INDEX_MAX;
+
+  switch (offset_size)
+    {
+      case SFRAME_FRE_OFFSET_1B:
+	index = SFRAME_FRE_OFFSET_FUNC_MAP_INDEX_1B;
+	break;
+      case SFRAME_FRE_OFFSET_2B:
+	index = SFRAME_FRE_OFFSET_FUNC_MAP_INDEX_2B;
+	break;
+      case SFRAME_FRE_OFFSET_4B:
+	index = SFRAME_FRE_OFFSET_FUNC_MAP_INDEX_4B;
+	break;
+      default:
+	/* Not supported in SFrame.  */
+	break;
+    }
+
+  return index;
+}
+
+/* Mapping from offset size to the output function to emit the value.  */
+
+static const
+struct sframe_fre_offset_func_map
+fre_offset_func_map[SFRAME_FRE_OFFSET_FUNC_MAP_INDEX_MAX+1] =
+{
+  { SFRAME_FRE_OFFSET_1B, out_one },
+  { SFRAME_FRE_OFFSET_2B, out_two },
+  { SFRAME_FRE_OFFSET_4B, out_four },
+  { -1, NULL } /* Not Supported in SFrame.  */
+};
+
+/* SFrame version specific operations access.  */
+
+static struct sframe_version_ops sframe_ver_ops;
+
+/* SFrame (SFRAME_VERSION_1) set FRE info.  */
+
+static unsigned char
+sframe_v1_set_fre_info (unsigned int base_reg, unsigned int num_offsets,
+			unsigned int offset_size)
+{
+  unsigned char fre_info;
+  fre_info = SFRAME_V1_FRE_INFO (base_reg, num_offsets, offset_size);
+  return fre_info;
+}
+
+/* SFrame (SFRAME_VERSION_1) set function info.  */
+static unsigned char
+sframe_v1_set_func_info (unsigned int fde_type, unsigned int fre_type)
+{
+  unsigned char func_info;
+  func_info = SFRAME_V1_FUNC_INFO (fde_type, fre_type);
+  return func_info;
+}
+
+/* SFrame version specific operations setup.  */
+
+static void
+sframe_set_version (uint32_t sframe_version __attribute__((unused)))
+{
+  sframe_ver_ops.format_version = SFRAME_VERSION_1;
+
+  sframe_ver_ops.set_fre_info = sframe_v1_set_fre_info;
+
+  sframe_ver_ops.set_func_info = sframe_v1_set_func_info;
+}
+
+/* SFrame set FRE info.  */
+
+static unsigned char
+sframe_set_fre_info (unsigned int base_reg, unsigned int num_offsets,
+		     unsigned int offset_size)
+{
+  return sframe_ver_ops.set_fre_info (base_reg, num_offsets,
+					 offset_size);
+}
+
+/* SFrame set func info. */
+
+ATTRIBUTE_UNUSED static unsigned char
+sframe_set_func_info (unsigned int fde_type, unsigned int fre_type)
+{
+  return sframe_ver_ops.set_func_info (fde_type, fre_type);
+}
+
+/* Get the number of SFrame FDEs for the current file.  */
+
+static unsigned int
+get_num_sframe_fdes (void);
+
+/* Get the number of SFrame frame row entries for the current file.  */
+
+static unsigned int
+get_num_sframe_fres (void);
+
+/* Get CFA base register ID as represented in SFrame Frame Row Entry.  */
+
+static unsigned int
+get_fre_base_reg_id (struct sframe_row_entry *sframe_fre)
+{
+  unsigned int cfi_insn_cfa_base_reg = sframe_fre->cfa_base_reg;
+  unsigned fre_base_reg = SFRAME_BASE_REG_SP;
+
+  if (cfi_insn_cfa_base_reg == SFRAME_CFA_FP_REG)
+    fre_base_reg = SFRAME_BASE_REG_FP;
+
+  /* Only one bit is reserved in SFRAME_VERSION_1.  */
+  gas_assert (fre_base_reg == SFRAME_BASE_REG_SP
+	      || fre_base_reg == SFRAME_BASE_REG_FP);
+
+  return fre_base_reg;
+}
+
+/* Get number of offsets necessary for the SFrame Frame Row Entry.  */
+
+static unsigned int
+get_fre_num_offsets (struct sframe_row_entry *sframe_fre)
+{
+  /* Atleast 1 must always be present (to recover CFA).  */
+  unsigned int fre_num_offsets = 1;
+
+  if (sframe_fre->bp_loc == SFRAME_FRE_ELEM_LOC_STACK)
+    fre_num_offsets++;
+#ifdef SFRAME_FRE_RA_TRACKING
+  if (sframe_fre->ra_loc == SFRAME_FRE_ELEM_LOC_STACK)
+    fre_num_offsets++;
+#endif
+  return fre_num_offsets;
+}
+
+/* Get the minimum necessary offset size (in bytes) for this
+   SFrame frame row entry.  */
+
+static unsigned int
+sframe_get_fre_offset_size (struct sframe_row_entry *sframe_fre)
+{
+  unsigned int max_offset_size = 0;
+  unsigned int cfa_offset_size = 0;
+  unsigned int bp_offset_size = 0;
+  unsigned int ra_offset_size = 0;
+
+  unsigned int fre_offset_size = 0;
+
+  /* What size of offsets appear in this frame row entry.  */
+  cfa_offset_size = get_offset_size_in_bytes (sframe_fre->cfa_offset);
+  if (sframe_fre->bp_loc == SFRAME_FRE_ELEM_LOC_STACK)
+    bp_offset_size = get_offset_size_in_bytes (sframe_fre->bp_offset);
+#ifdef SFRAME_FRE_RA_TRACKING
+  if (sframe_ra_tracking_p ()
+      && sframe_fre->ra_loc == SFRAME_FRE_ELEM_LOC_STACK)
+    ra_offset_size = get_offset_size_in_bytes (sframe_fre->ra_offset);
+#endif
+
+  /* Get the maximum size needed to represent the offsets.  */
+  max_offset_size = cfa_offset_size;
+  if (bp_offset_size > max_offset_size)
+    max_offset_size = bp_offset_size;
+  if (ra_offset_size > max_offset_size)
+    max_offset_size = ra_offset_size;
+
+  gas_assert (max_offset_size);
+
+  switch (max_offset_size)
+    {
+    case 1:
+      fre_offset_size = SFRAME_FRE_OFFSET_1B;
+      break;
+    case 2:
+      fre_offset_size = SFRAME_FRE_OFFSET_2B;
+      break;
+    case 4:
+      fre_offset_size = SFRAME_FRE_OFFSET_4B;
+      break;
+    default:
+      /* Offset of size 8 bytes is not supported in SFrame format
+	 version 1.  */
+      as_fatal (_("SFrame unsupported offset value\n"));
+      break;
+    }
+
+  return fre_offset_size;
+}
+
+#if SFRAME_FRE_TYPE_SELECTION_OPT
+
+/* Create a composite exression CEXP (for SFrame FRE start address) such that:
+
+      exp = <val> OP_absent <width>, where,
+
+    - <val> and <width> are themselves expressionS.
+    - <val> stores the expression which when evaluated gives the value of the
+      start address offset of the FRE.
+    - <width> stores the expression when when evaluated gives the number of
+      bytes needed to encode the start address offset of the FRE.
+
+   The use of OP_absent as the X_op_symbol helps identify this expression
+   later when fragments are fixed up.  */
+
+static void
+create_fre_start_addr_exp (expressionS *cexp, symbolS *fre_pc_begin,
+			   symbolS *fde_start_address,
+			   symbolS *fde_end_address)
+{
+  expressionS val;
+  expressionS width;
+
+  /* val expression stores the FDE start address offset from the start PC
+     of function.  */
+  val.X_op = O_subtract;
+  val.X_add_symbol = fre_pc_begin;
+  val.X_op_symbol = fde_start_address;
+  val.X_add_number = 0;
+
+  /* width expressions stores the size of the function.  This is used later
+     to determine the number of bytes to be used to encode the FRE start
+     address of each FRE of the function.  */
+  width.X_op = O_subtract;
+  width.X_add_symbol = fde_end_address;
+  width.X_op_symbol = fde_start_address;
+  width.X_add_number = 0;
+
+  cexp->X_op = O_absent;
+  cexp->X_add_symbol = make_expr_symbol (&val);
+  cexp->X_op_symbol = make_expr_symbol (&width);
+  cexp->X_add_number = 0;
+}
+
+#endif
+
+static void
+output_sframe_row_entry (symbolS *fde_start_addr,
+			 symbolS *fde_end_addr,
+			 struct sframe_row_entry *sframe_fre)
+{
+  unsigned char fre_info;
+  unsigned int fre_num_offsets;
+  unsigned int fre_offset_size;
+  unsigned int fre_base_reg;
+  expressionS exp;
+  unsigned int fre_addr_size;
+
+  unsigned int index = 0;
+  unsigned int fre_write_offsets = 0;
+
+  fre_addr_size = 4; /* 4 bytes by default.   FIXME tie it to fre_type? */
+
+  /* SFrame FRE Start Address.  */
+#if SFRAME_FRE_TYPE_SELECTION_OPT
+  create_fre_start_addr_exp (&exp, sframe_fre->pc_begin, fde_start_addr,
+			     fde_end_addr);
+  frag_grow (fre_addr_size);
+  frag_var (rs_sframe, fre_addr_size, 0, (relax_substateT) 0,
+	    make_expr_symbol (&exp), 0, (char *) frag_now);
+#else
+  gas_assert (fde_end_addr);
+  exp.X_op = O_subtract;
+  exp.X_add_symbol = sframe_fre->pc_begin; /* to.  */
+  exp.X_op_symbol = fde_start_addr; /* from.  */
+  exp.X_add_number = 0;
+  emit_expr (&exp, fre_addr_size);
+#endif
+
+  /* Create the fre_info using the CFA base register, number of offsets and max
+     size of offset in this frame row entry.  */
+  fre_base_reg = get_fre_base_reg_id (sframe_fre);
+  fre_num_offsets = get_fre_num_offsets (sframe_fre);
+  fre_offset_size = sframe_get_fre_offset_size (sframe_fre);
+  fre_info = sframe_set_fre_info (fre_base_reg, fre_num_offsets,
+				     fre_offset_size);
+  out_one (fre_info);
+
+  index = sframe_fre_offset_func_map_index (fre_offset_size);
+  gas_assert (index < SFRAME_FRE_OFFSET_FUNC_MAP_INDEX_MAX);
+
+  /* Write out the offsets in order - cfa, bp, ra.  */
+  fre_offset_func_map[index].out_func (sframe_fre->cfa_offset);
+  fre_write_offsets++;
+
+#ifdef SFRAME_FRE_RA_TRACKING
+  if (sframe_fre->ra_loc == SFRAME_FRE_ELEM_LOC_STACK)
+    {
+      fre_offset_func_map[index].out_func (sframe_fre->ra_offset);
+      fre_write_offsets++;
+    }
+#endif
+  if (sframe_fre->bp_loc == SFRAME_FRE_ELEM_LOC_STACK)
+    {
+      fre_offset_func_map[index].out_func (sframe_fre->bp_offset);
+      fre_write_offsets++;
+    }
+
+  /* Check if the expected number offsets have been written out
+     in this FRE.  */
+  gas_assert (fre_write_offsets == fre_num_offsets);
+}
+
+static void
+output_sframe_funcdesc (symbolS *start_of_fre_section,
+			symbolS *fre_symbol,
+			struct sframe_func_entry *sframe_fde)
+{
+  expressionS exp;
+  unsigned int addr_size;
+  symbolS *dw_fde_start_addrS, *dw_fde_end_addrS;
+
+  addr_size = SFRAME_RELOC_SIZE;
+  dw_fde_start_addrS = get_dw_fde_start_addrS (sframe_fde->dw_fde);
+  dw_fde_end_addrS = get_dw_fde_end_addrS (sframe_fde->dw_fde);
+
+  /* Start address of the function.  */
+  exp.X_op = O_subtract;
+  exp.X_add_symbol = dw_fde_start_addrS; /* to location.  */
+  exp.X_op_symbol = symbol_temp_new_now (); /* from location.  */
+  exp.X_add_number = 0;
+  emit_expr (&exp, addr_size);
+
+  /* Size of the function in bytes.  */
+  exp.X_op = O_subtract;
+  exp.X_add_symbol = dw_fde_end_addrS;
+  exp.X_op_symbol = dw_fde_start_addrS;
+  exp.X_add_number = 0;
+  emit_expr (&exp, addr_size);
+
+  /* Offset to the first frame row entry.  */
+  exp.X_op = O_subtract;
+  exp.X_add_symbol = fre_symbol; /* Minuend.  */
+  exp.X_op_symbol = start_of_fre_section; /* Subtrahend.  */
+  exp.X_add_number = 0;
+  emit_expr (&exp, addr_size);
+
+  /* Number of FREs.  */
+  out_four (sframe_fde->num_fres);
+
+  /* SFrame FDE function info.  */
+#if SFRAME_FRE_TYPE_SELECTION_OPT
+  expressionS width;
+  width.X_op = O_subtract;
+  width.X_add_symbol = dw_fde_end_addrS;
+  width.X_op_symbol = dw_fde_start_addrS;
+  width.X_add_number = 0;
+  frag_grow (1); /* Size of func info is unsigned char.  */
+  frag_var (rs_sframe, 1, 0, (relax_substateT) 0,
+	    make_expr_symbol (&width), 0, (char *) frag_now);
+#else
+  unsigned char func_info;
+  func_info = sframe_set_func_info (SFRAME_FDE_TYPE_PCINC,
+				    SFRAME_FRE_TYPE_ADDR4);
+  out_one (func_info);
+#endif
+}
+
+static void
+output_sframe_internal (void)
+{
+  expressionS exp;
+  unsigned int i = 0;
+
+  symbolS *end_of_frame_hdr;
+  symbolS *end_of_frame_section;
+  symbolS *start_of_func_desc_section;
+  symbolS *start_of_fre_section;
+  struct sframe_func_entry *sframe_fde;
+  struct sframe_row_entry *sframe_fre;
+  unsigned char abi_arch = 0;
+  int fixed_bp_offset = SFRAME_CFA_FIXED_FP_INVALID;
+  int fixed_ra_offset = SFRAME_CFA_FIXED_RA_INVALID;
+  unsigned int addr_size;
+
+  addr_size = SFRAME_RELOC_SIZE;
+
+  /* The function desciptor entries as dumped by the assembler are not
+     sorted on PCs.  */
+  unsigned char sframe_flags = 0;
+  sframe_flags |= !SFRAME_F_FDE_SORTED;
+
+  unsigned int num_fdes = get_num_sframe_fdes ();
+  unsigned int num_fres = get_num_sframe_fres ();
+  symbolS **fre_symbols = XNEWVEC (symbolS *, num_fres);
+  for (i = 0; i < num_fres; i++)
+    fre_symbols[i] = symbol_temp_make ();
+
+  end_of_frame_hdr = symbol_temp_make ();
+  start_of_fre_section = symbol_temp_make ();
+  start_of_func_desc_section = symbol_temp_make ();
+  end_of_frame_section = symbol_temp_make ();
+
+  /* Output the preamble of SFrame section.  */
+  out_two (SFRAME_MAGIC);
+  out_one (SFRAME_VERSION);
+  out_one (sframe_flags);
+  /* abi/arch.  */
+#ifdef sframe_get_abi_arch
+  abi_arch = sframe_get_abi_arch ();
+#endif
+  gas_assert (abi_arch);
+  out_one (abi_arch);
+
+  /* Offset for the BP register from CFA.  Neither of the AMD64 or AAPCS64
+     ABIs have a fixed offset for the BP register from the CFA.  This may be
+     useful in future (but not without additional support in the toolchain)
+     for specialized handling/encoding for cases where, for example,
+     -fno-omit-frame-pointer is used.  */
+  out_one (fixed_bp_offset);
+
+  /* Offset for the return address from CFA is fixed for some ABIs
+     (e.g., AMD64), output a zero otherwise.  */
+#ifdef sframe_ra_tracking_p
+  if (!sframe_ra_tracking_p ())
+    fixed_ra_offset = sframe_cfa_ra_offset ();
+#endif
+  out_one (fixed_ra_offset);
+
+  /* None of the AMD64, or AARCH64 ABIs need the auxilliary header.
+     When the need does arise to use this field, the appropriate backend
+     must provide this information.  */
+  out_one (0); /* Auxilliary SFrame header length.  */
+
+  out_four (num_fdes); /* Number of FDEs.  */
+  out_four (num_fres); /* Number of FREs.  */
+
+  /* FRE sub-section len.  */
+  exp.X_op = O_subtract;
+  exp.X_add_symbol = end_of_frame_section;
+  exp.X_op_symbol = start_of_fre_section;
+  exp.X_add_number = 0;
+  emit_expr (&exp, addr_size);
+
+  /* Offset of Function Index sub-section.  */
+  exp.X_op = O_subtract;
+  exp.X_add_symbol = end_of_frame_hdr;
+  exp.X_op_symbol = start_of_func_desc_section;
+  exp.X_add_number = 0;
+  emit_expr (&exp, addr_size);
+
+  /* Offset of FRE sub-section.  */
+  exp.X_op = O_subtract;
+  exp.X_add_symbol = start_of_fre_section;
+  exp.X_op_symbol = end_of_frame_hdr;
+  exp.X_add_number = 0;
+  emit_expr (&exp, addr_size);
+
+  symbol_set_value_now (end_of_frame_hdr);
+  symbol_set_value_now (start_of_func_desc_section);
+
+  /* Output the SFrame function descriptor entries.  */
+  i = 0;
+  for (sframe_fde = all_sframe_fdes; sframe_fde; sframe_fde = sframe_fde->next)
+    {
+      output_sframe_funcdesc (start_of_fre_section,
+			      fre_symbols[i], sframe_fde);
+      i += sframe_fde->num_fres;
+    }
+
+  symbol_set_value_now (start_of_fre_section);
+
+  /* Output the SFrame FREs.  */
+  i = 0;
+  sframe_fde = all_sframe_fdes;
+
+  for (sframe_fde = all_sframe_fdes; sframe_fde; sframe_fde = sframe_fde->next)
+    {
+      for (sframe_fre = sframe_fde->sframe_fres;
+	   sframe_fre;
+	   sframe_fre = sframe_fre->next)
+	{
+	  symbol_set_value_now (fre_symbols[i]);
+	  output_sframe_row_entry (get_dw_fde_start_addrS (sframe_fde->dw_fde),
+				   get_dw_fde_end_addrS (sframe_fde->dw_fde),
+				   sframe_fre);
+	  i++;
+	}
+    }
+
+  symbol_set_value_now (end_of_frame_section);
+
+  gas_assert (i == num_fres);
+
+  free (fre_symbols);
+  fre_symbols = NULL;
+}
+
+/* List of SFrame FDE entries.  */
+
+struct sframe_func_entry *all_sframe_fdes;
+
+/* Tail of the list to add to.  */
+
+static struct sframe_func_entry **last_sframe_fde = &all_sframe_fdes;
+
+static unsigned int
+get_num_sframe_fdes (void)
+{
+  struct sframe_func_entry *sframe_fde;
+  unsigned int total_fdes = 0;
+
+  for (sframe_fde = all_sframe_fdes; sframe_fde ; sframe_fde = sframe_fde->next)
+    total_fdes++;
+
+  return total_fdes;
+}
+
+/* Get the total number of SFrame row entries across the FDEs.  */
+
+static unsigned int
+get_num_sframe_fres (void)
+{
+  struct sframe_func_entry *sframe_fde;
+  unsigned int total_fres = 0;
+
+  for (sframe_fde = all_sframe_fdes; sframe_fde ; sframe_fde = sframe_fde->next)
+    total_fres += sframe_fde->num_fres;
+
+  return total_fres;
+}
+
+/* Allocate an SFrame FDE.  */
+
+static struct sframe_func_entry*
+sframe_fde_alloc (void)
+{
+  struct sframe_func_entry *sframe_fde = XCNEW (struct sframe_func_entry);
+  return sframe_fde;
+}
+
+/* Link the SFrame FDE in.  */
+
+static int
+sframe_fde_link (struct sframe_func_entry *sframe_fde)
+{
+  *last_sframe_fde = sframe_fde;
+  last_sframe_fde = &sframe_fde->next;
+
+  return 0;
+}
+
+/* Free up the SFrame FDE.  */
+
+static void
+sframe_fde_free (struct sframe_func_entry *sframe_fde)
+{
+  XDELETE (sframe_fde);
+  sframe_fde = NULL;
+}
+
+/* SFrame translation context functions.  */
+
+/* Allocate a new SFrame translation context.  */
+
+static struct sframe_xlate_ctx*
+sframe_xlate_ctx_alloc (void)
+{
+  struct sframe_xlate_ctx* xlate_ctx = XCNEW (struct sframe_xlate_ctx);
+  return xlate_ctx;
+}
+
+/* Initialize the given SFrame translation context.  */
+
+static void
+sframe_xlate_ctx_init (struct sframe_xlate_ctx *xlate_ctx)
+{
+  xlate_ctx->dw_fde = NULL;
+  xlate_ctx->first_fre = NULL;
+  xlate_ctx->last_fre = NULL;
+  xlate_ctx->cur_fre = NULL;
+  xlate_ctx->remember_fre = NULL;
+  xlate_ctx->num_xlate_fres = 0;
+}
+
+/* Cleanup the given SFrame translation context.  */
+
+static void
+sframe_xlate_ctx_cleanup (struct sframe_xlate_ctx *xlate_ctx)
+{
+  struct sframe_row_entry *fre, *fre_next;
+
+  if (xlate_ctx->num_xlate_fres)
+    {
+      fre = xlate_ctx->first_fre;
+      while (fre)
+	{
+	  fre_next = fre->next;
+	  XDELETE (fre);
+	  fre = fre_next;
+	}
+    }
+
+  sframe_xlate_ctx_init (xlate_ctx);
+}
+
+/* Transfer the state from the SFrame translation context to the SFrame FDE.  */
+
+static void
+sframe_xlate_ctx_finalize (struct sframe_xlate_ctx *xlate_ctx,
+			   struct sframe_func_entry *sframe_fde)
+{
+  sframe_fde->dw_fde = xlate_ctx->dw_fde;
+  sframe_fde->sframe_fres = xlate_ctx->first_fre;
+  sframe_fde->num_fres = xlate_ctx->num_xlate_fres;
+}
+
+static struct sframe_row_entry*
+sframe_row_entry_new (void)
+{
+  struct sframe_row_entry *fre = XCNEW (struct sframe_row_entry);
+  /* Reset cfa_base_reg to -1.  A value of 0 will imply some valid register
+     for the supported arches.  */
+  fre->cfa_base_reg = -1;
+  fre->merge_candidate = true;
+
+  return fre;
+}
+
+/* Add the given FRE in the list of frame row entries in the given FDE
+   translation context.  */
+
+static void
+sframe_xlate_ctx_add_fre (struct sframe_xlate_ctx *xlate_ctx,
+			 struct sframe_row_entry *fre)
+{
+  gas_assert (xlate_ctx && fre);
+
+  /* Add the frame row entry.  */
+  if (!xlate_ctx->first_fre)
+    xlate_ctx->first_fre = fre;
+  else if (xlate_ctx->last_fre)
+    xlate_ctx->last_fre->next = fre;
+
+  xlate_ctx->last_fre = fre;
+
+  /* Keep track of the total number of SFrame frame row entries.  */
+  xlate_ctx->num_xlate_fres++;
+}
+
+/* A SFrame Frame Row Entry is self-sufficient in terms of unwind information
+   for a given PC.  It contains information assimilated from multiple CFI
+   instructions, and hence, a new SFrame FRE is initialized with the data from
+   the previous known FRE, if any.
+
+   Understandably, not all information (especially the instruction begin
+   and end boundaries) needs to be relayed.  Hence, the caller of this API
+   must set the pc_begin and pc_end as applicable.  */
+
+static void
+sframe_row_entry_initialize (struct sframe_row_entry *cur_fre,
+			     struct sframe_row_entry *prev_fre)
+{
+  gas_assert (prev_fre);
+  cur_fre->cfa_base_reg = prev_fre->cfa_base_reg;
+  cur_fre->cfa_offset = prev_fre->cfa_offset;
+  cur_fre->bp_loc = prev_fre->bp_loc;
+  cur_fre->bp_offset = prev_fre->bp_offset;
+  cur_fre->ra_loc = prev_fre->ra_loc;
+  cur_fre->ra_offset = prev_fre->ra_offset;
+}
+
+/* Translate DW_CFA_advance_loc into SFrame context.
+   Return SFRAME_XLATE_OK if success.  */
+
+static int
+sframe_xlate_do_advance_loc (struct sframe_xlate_ctx *xlate_ctx,
+			     struct cfi_insn_data *cfi_insn)
+{
+  struct sframe_row_entry *last_fre = xlate_ctx->last_fre;
+  /* Get the scratchpad FRE currently being updated as the cfi_insn's
+     get interpreted.  This FRE eventually gets linked in into the
+     list of FREs for the specific function.  */
+  struct sframe_row_entry *cur_fre = xlate_ctx->cur_fre;
+
+  if (cur_fre)
+    {
+      if (!cur_fre->merge_candidate)
+	{
+	  sframe_fre_set_end_addr (cur_fre, cfi_insn->u.ll.lab2);
+
+	  sframe_xlate_ctx_add_fre (xlate_ctx, cur_fre);
+	  last_fre = xlate_ctx->last_fre;
+
+	  xlate_ctx->cur_fre = sframe_row_entry_new ();
+	  cur_fre = xlate_ctx->cur_fre;
+
+	  if (last_fre)
+	    sframe_row_entry_initialize (cur_fre, last_fre);
+	}
+      else
+	{
+	  sframe_fre_set_end_addr (last_fre, cfi_insn->u.ll.lab2);
+	  gas_assert (last_fre->merge_candidate == false);
+	}
+    }
+  else
+    {
+      xlate_ctx->cur_fre = sframe_row_entry_new ();
+      cur_fre = xlate_ctx->cur_fre;
+    }
+
+  gas_assert (cur_fre);
+  sframe_fre_set_begin_addr (cur_fre, cfi_insn->u.ll.lab2);
+
+  return SFRAME_XLATE_OK;
+}
+
+/* Translate DW_CFA_def_cfa into SFrame context.
+   Return SFRAME_XLATE_OK if success.  */
+
+static int
+sframe_xlate_do_def_cfa (struct sframe_xlate_ctx *xlate_ctx,
+			 struct cfi_insn_data *cfi_insn)
+
+{
+  /* Get the scratchpad FRE.  This FRE will eventually get linked in.  */
+  struct sframe_row_entry *cur_fre = xlate_ctx->cur_fre;
+  if (!cur_fre)
+  {
+    xlate_ctx->cur_fre = sframe_row_entry_new ();
+    cur_fre = xlate_ctx->cur_fre;
+    sframe_fre_set_begin_addr (cur_fre,
+			       get_dw_fde_start_addrS (xlate_ctx->dw_fde));
+  }
+  /* Define the current CFA rule to use the provided register and
+     offset.  */
+  sframe_fre_set_cfa_base_reg (cur_fre, cfi_insn->u.ri.reg);
+  sframe_fre_set_cfa_offset (cur_fre, cfi_insn->u.ri.offset);
+  cur_fre->merge_candidate = false;
+
+  return SFRAME_XLATE_OK;
+}
+
+/* Translate DW_CFA_def_cfa_register into SFrame context.
+   Return SFRAME_XLATE_OK if success.  */
+
+static int
+sframe_xlate_do_def_cfa_register (struct sframe_xlate_ctx *xlate_ctx,
+				  struct cfi_insn_data *cfi_insn)
+{
+  struct sframe_row_entry *last_fre = xlate_ctx->last_fre;
+  /* Get the scratchpad FRE.  This FRE will eventually get linked in.  */
+  struct sframe_row_entry *cur_fre = xlate_ctx->cur_fre;
+  gas_assert (cur_fre);
+  /* Define the current CFA rule to use the provided register (but to
+     keep the old offset).  */
+  sframe_fre_set_cfa_base_reg (cur_fre, cfi_insn->u.ri.reg);
+  sframe_fre_set_cfa_offset (cur_fre, last_fre->cfa_offset);
+  cur_fre->merge_candidate = false;
+
+  return SFRAME_XLATE_OK;
+}
+
+/* Translate DW_CFA_def_cfa_offset into SFrame context.
+   Return SFRAME_XLATE_OK if success.  */
+
+static int
+sframe_xlate_do_def_cfa_offset (struct sframe_xlate_ctx *xlate_ctx,
+				struct cfi_insn_data *cfi_insn)
+{
+  /* The scratchpad FRE currently being updated with each cfi_insn
+     being interpreted.  This FRE eventually gets linked in into the
+     list of FREs for the specific function.  */
+  struct sframe_row_entry *cur_fre = xlate_ctx->cur_fre;
+
+  gas_assert (cur_fre);
+  /*  Define the current CFA rule to use the provided offset (but to keep
+      the old register).  However, if the old register is not FP/SP,
+      skip creating SFrame unwind info for the function. */
+  if ((cur_fre->cfa_base_reg == SFRAME_CFA_FP_REG)
+      || (cur_fre->cfa_base_reg == SFRAME_CFA_SP_REG))
+    {
+      sframe_fre_set_cfa_offset (cur_fre, cfi_insn->u.i);
+      cur_fre->merge_candidate = false;
+    }
+  else
+    return SFRAME_XLATE_ERR_NOTREPRESENTED;
+
+  return SFRAME_XLATE_OK;
+}
+
+/* Translate DW_CFA_offset into SFrame context.
+   Return SFRAME_XLATE_OK if success.  */
+
+static int
+sframe_xlate_do_offset (struct sframe_xlate_ctx *xlate_ctx,
+			struct cfi_insn_data *cfi_insn)
+{
+  /* The scratchpad FRE currently being updated with each cfi_insn
+     being interpreted.  This FRE eventually gets linked in into the
+     list of FREs for the specific function.  */
+  struct sframe_row_entry *cur_fre = xlate_ctx->cur_fre;
+
+  gas_assert (cur_fre);
+  /* Change the rule for the register indicated by the register number to
+     be the specified offset.  */
+  if (cfi_insn->u.r == SFRAME_CFA_FP_REG)
+    {
+      gas_assert (!cur_fre->base_reg);
+      sframe_fre_set_bp_track (cur_fre, cfi_insn->u.ri.offset);
+      cur_fre->merge_candidate = false;
+    }
+#ifdef SFRAME_FRE_RA_TRACKING
+  else if (sframe_ra_tracking_p ()
+	   && cfi_insn->u.r == SFRAME_CFA_RA_REG)
+    {
+      sframe_fre_set_ra_track (cur_fre, cfi_insn->u.ri.offset);
+      cur_fre->merge_candidate = false;
+    }
+#endif
+  /* This is used to track changes to non-rsp registers, skip all others
+     except FP / RA for now.  */
+  return SFRAME_XLATE_OK;
+}
+
+/* Translate DW_CFA_val_offset into SFrame context.
+   Return SFRAME_XLATE_OK if success.  */
+
+static int
+sframe_xlate_do_val_offset (struct sframe_xlate_ctx *xlate_ctx ATTRIBUTE_UNUSED,
+			    struct cfi_insn_data *cfi_insn)
+{
+  /* Previous value of register is CFA + offset.  However, if the specified
+     register is not interesting (FP or RA reg), the current DW_CFA_val_offset
+     instruction can be safely skipped without sacrificing the asynchonicity of
+     unwind information.  */
+  if (cfi_insn->u.r == SFRAME_CFA_FP_REG)
+    return SFRAME_XLATE_ERR_NOTREPRESENTED; /* Not represented.  */
+#ifdef SFRAME_FRE_RA_TRACKING
+  else if (sframe_ra_tracking_p ()
+	   && cfi_insn->u.r == SFRAME_CFA_RA_REG)
+    return SFRAME_XLATE_ERR_NOTREPRESENTED; /* Not represented.  */
+#endif
+
+  /* Safe to skip.  */
+  return SFRAME_XLATE_OK;
+}
+
+/* Translate DW_CFA_remember_state into SFrame context.
+   Return SFRAME_XLATE_OK if success.  */
+
+static int
+sframe_xlate_do_remember_state (struct sframe_xlate_ctx *xlate_ctx)
+{
+  struct sframe_row_entry *last_fre = xlate_ctx->last_fre;
+
+  /* If there is no FRE state to remember, nothing to do here.  Return
+     early with non-zero error code, this will cause no SFrame unwind info
+     for the function involved.  */
+  if (!last_fre)
+    return SFRAME_XLATE_ERR_INVAL;
+
+  if (!xlate_ctx->remember_fre)
+    xlate_ctx->remember_fre = sframe_row_entry_new ();
+  sframe_row_entry_initialize (xlate_ctx->remember_fre, last_fre);
+
+  return SFRAME_XLATE_OK;
+}
+
+/* Translate DW_CFA_restore_state into SFrame context.
+   Return SFRAME_XLATE_OK if success.  */
+
+static int
+sframe_xlate_do_restore_state (struct sframe_xlate_ctx *xlate_ctx)
+{
+  /* The scratchpad FRE currently being updated with each cfi_insn
+     being interpreted.  This FRE eventually gets linked in into the
+     list of FREs for the specific function.  */
+  struct sframe_row_entry *cur_fre = xlate_ctx->cur_fre;
+
+  gas_assert (xlate_ctx->remember_fre);
+  gas_assert (cur_fre && cur_fre->merge_candidate);
+
+  /* Get the CFA state from the DW_CFA_remember_state insn.  */
+  sframe_row_entry_initialize (cur_fre, xlate_ctx->remember_fre);
+  /* The PC boundaries of the current SFrame FRE are updated
+     via other machinery.  */
+  cur_fre->merge_candidate = false;
+  return SFRAME_XLATE_OK;
+}
+
+/* Translate DW_CFA_restore into SFrame context.
+   Return SFRAME_XLATE_OK if success.  */
+
+static int
+sframe_xlate_do_restore (struct sframe_xlate_ctx *xlate_ctx,
+			 struct cfi_insn_data *cfi_insn)
+{
+  struct sframe_row_entry *cie_fre = xlate_ctx->first_fre;
+  /* The scratchpad FRE currently being updated with each cfi_insn
+     being interpreted.  This FRE eventually gets linked in into the
+     list of FREs for the specific function.  */
+  struct sframe_row_entry *cur_fre = xlate_ctx->cur_fre;
+
+  /* Change the rule for the indicated register to the rule assigned to
+     it by the initial_instructions in the CIE.  */
+  gas_assert (cie_fre);
+  /* SFrame FREs track only CFA and FP / RA for backtracing purposes;
+     skip the other .cfi_restore directives.  */
+  if (cfi_insn->u.r == SFRAME_CFA_FP_REG)
+    {
+      gas_assert (cur_fre);
+      cur_fre->bp_loc = cie_fre->bp_loc;
+      cur_fre->bp_offset = cie_fre->bp_offset;
+      cur_fre->merge_candidate = false;
+    }
+#ifdef SFRAME_FRE_RA_TRACKING
+  else if (sframe_ra_tracking_p ()
+	   && cfi_insn->u.r == SFRAME_CFA_RA_REG)
+    {
+      gas_assert (cur_fre);
+      cur_fre->ra_loc = cie_fre->ra_loc;
+      cur_fre->ra_offset = cie_fre->ra_offset;
+      cur_fre->merge_candidate = false;
+    }
+#endif
+  return SFRAME_XLATE_OK;
+}
+
+/* Process CFI_INSN and update the translation context with the FRE
+   information.
+
+   Returns an error code (sframe_xlate_err) if CFI_INSN is not successfully
+   processed.  */
+
+static int
+sframe_do_cfi_insn (struct sframe_xlate_ctx *xlate_ctx,
+		    struct cfi_insn_data *cfi_insn)
+{
+  int err = 0;
+
+  /* Atleast one cfi_insn per FDE is expected.  */
+  gas_assert (cfi_insn);
+  int op = cfi_insn->insn;
+
+  switch (op)
+    {
+    case DW_CFA_advance_loc:
+      err = sframe_xlate_do_advance_loc (xlate_ctx, cfi_insn);
+      break;
+    case DW_CFA_def_cfa:
+      err = sframe_xlate_do_def_cfa (xlate_ctx, cfi_insn);
+      break;
+    case DW_CFA_def_cfa_register:
+      err = sframe_xlate_do_def_cfa_register (xlate_ctx, cfi_insn);
+      break;
+    case DW_CFA_def_cfa_offset:
+      err = sframe_xlate_do_def_cfa_offset (xlate_ctx, cfi_insn);
+      break;
+    case DW_CFA_offset:
+      err = sframe_xlate_do_offset (xlate_ctx, cfi_insn);
+      break;
+    case DW_CFA_val_offset:
+      err = sframe_xlate_do_val_offset (xlate_ctx, cfi_insn);
+      break;
+    case DW_CFA_remember_state:
+      err = sframe_xlate_do_remember_state (xlate_ctx);
+      break;
+    case DW_CFA_restore_state:
+      err = sframe_xlate_do_restore_state (xlate_ctx);
+      break;
+    case DW_CFA_restore:
+      err = sframe_xlate_do_restore (xlate_ctx, cfi_insn);
+      break;
+    case DW_CFA_undefined:
+    case DW_CFA_same_value:
+      break;
+    default:
+      {
+	/* Other CFI opcodes are not processed at this time.
+	   These do not impact the coverage of the basic stack unwinding
+	   information as conveyed in the SFrame format.
+	    - DW_CFA_register,
+	    - ...
+
+	   Following skipped operations do, however, impact the asynchronicity:
+	     - CFI_escape,
+	     - DW_CFA_GNU_window_save,
+	     - DW_CFA_AARCH64_negate_ra_state (multiplexed with
+	       DW_CFA_GNU_window_save)  */
+
+	err = SFRAME_XLATE_ERR_NOTREPRESENTED;
+	// printf (_("SFrame Unsupported or unknown Dwarf CFI number: %#x\n"), op);
+      }
+    }
+
+  return err;
+}
+
+
+static int
+sframe_do_fde (struct sframe_xlate_ctx *xlate_ctx,
+	       const struct fde_entry *dw_fde)
+{
+  struct cfi_insn_data *cfi_insn;
+  int err = SFRAME_XLATE_OK;
+
+  xlate_ctx->dw_fde = dw_fde;
+
+  /* If the return column is not RIP, SFrame format cannot represent it.  */
+  if (xlate_ctx->dw_fde->return_column != DWARF2_DEFAULT_RETURN_COLUMN)
+    return SFRAME_XLATE_ERR_NOTREPRESENTED;
+
+  /* Iterate over the CFIs and create SFrame FREs.  */
+  for (cfi_insn = dw_fde->data; cfi_insn; cfi_insn = cfi_insn->next)
+    {
+      /* Translate each CFI, and buffer the state in translation context.  */
+      err = sframe_do_cfi_insn (xlate_ctx, cfi_insn);
+      if (err != SFRAME_XLATE_OK)
+	{
+	  /* Skip generating SFrame unwind info for the function if any
+	     offending CFI is encountered by sframe_do_cfi_insn ().  */
+	  return err; /* Return the error code.  */
+	}
+    }
+
+  /* No errors encountered.  */
+
+  /* Link in the scratchpad FRE that the last few CFI insns helped create.  */
+  if (xlate_ctx->cur_fre)
+    {
+      sframe_xlate_ctx_add_fre (xlate_ctx, xlate_ctx->cur_fre);
+      xlate_ctx->cur_fre = NULL;
+    }
+  /* Designate the end of the last SFrame FRE.  */
+  if (xlate_ctx->last_fre)
+    {
+      xlate_ctx->last_fre->pc_end
+	= get_dw_fde_end_addrS (xlate_ctx->dw_fde);
+    }
+
+  return SFRAME_XLATE_OK;
+}
+
+/* Create SFrame unwind info for all functions.
+
+   This function consumes the already generated FDEs (by dw2gencfi) and
+   generates unwind data in SFrame format.  */
+
+static void
+create_sframe_all (void)
+{
+  struct fde_entry *dw_fde = NULL;
+  struct sframe_func_entry *sframe_fde = NULL;
+
+  struct sframe_xlate_ctx *xlate_ctx = sframe_xlate_ctx_alloc ();
+
+  for (dw_fde = all_fde_data; dw_fde ; dw_fde = dw_fde->next)
+    {
+      sframe_fde = sframe_fde_alloc ();
+      /* Initialize the translation context with information anew.  */
+      sframe_xlate_ctx_init (xlate_ctx);
+
+      /* Process and link SFrame FDEs if no error.  Also skip adding an SFrame
+	 FDE if it does not contain any SFrame FREs.  There is little use of an
+	 SFrame FDE if there is no unwind information about the function.  */
+      int err = sframe_do_fde (xlate_ctx, dw_fde);
+      if (err || xlate_ctx->num_xlate_fres == 0)
+	{
+	  sframe_xlate_ctx_cleanup (xlate_ctx);
+	  sframe_fde_free (sframe_fde);
+	}
+      else
+	{
+	  /* All done.  Transfer the state from the SFrame translation
+	     context to the SFrame FDE.  */
+	  sframe_xlate_ctx_finalize (xlate_ctx, sframe_fde);
+	  sframe_fde_link (sframe_fde);
+	}
+    }
+}
+
+void
+output_sframe (segT sframe_seg)
+{
+  (void) sframe_seg;
+
+  /* Setup the version specific access functions.  */
+  sframe_set_version (SFRAME_VERSION_1);
+
+  /* Process all fdes and create SFrame unwind information.  */
+  create_sframe_all ();
+
+  output_sframe_internal ();
+}
+
+#else  /*  support_sframe_p  */
+
+void
+output_sframe (segT sframe_seg __attribute__((unused)))
+{
+}
+
+#endif /*  support_sframe_p  */
diff --git a/gas/gen-sframe.h b/gas/gen-sframe.h
new file mode 100644
index 0000000..93af499
--- /dev/null
+++ b/gas/gen-sframe.h
@@ -0,0 +1,153 @@
+/* gen-sframe.h - Support for generating SFrame.
+   Copyright (C) 2022 Free Software Foundation, Inc.
+
+   This file is part of GAS, the GNU Assembler.
+
+   GAS is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3, or (at your option)
+   any later version.
+
+   GAS is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with GAS; see the file COPYING.  If not, write to the Free
+   Software Foundation, 51 Franklin Street - Fifth Floor, Boston, MA
+   02110-1301, USA.  */
+
+#ifndef GENSFRAME_H
+#define GENSFRAME_H
+
+#define SFRAME_FRE_ELEM_LOC_REG		0
+#define SFRAME_FRE_ELEM_LOC_STACK	1
+
+/* SFrame Frame Row Entry (FRE).
+
+   A frame row entry is a slice of the frame and can be valid for a set of
+   program instructions.  It keeps all information needed to retrieve the CFA
+   and the Return Address (RA) if tracked.
+
+   A frame row entry effectively stores accumulated information gathered by
+   interpreting multiple CFI instructions.  More precisely, it is a
+   self-sufficient record in its own right.  Only the subset of information
+   necessary for unwinding is stored: Given a PC, how to retrieve the CFA and
+   the RA.
+*/
+
+struct sframe_row_entry
+{
+  /* A linked list.  */
+  struct sframe_row_entry *next;
+
+  /* Start and end of the frame row entry.  */
+  symbolS *pc_begin;
+  symbolS *pc_end;
+
+  /* A frame row entry is a merge candidate if new information can be updated
+     on it.  */
+  bool merge_candidate;
+
+  /* Track CFA base (architectural) register ID.  */
+  unsigned int cfa_base_reg;
+  /* Offset from the CFA base register for recovering CFA.  */
+  offsetT cfa_offset;
+
+  /* Track the other register used as base register for CFA.  Specify whether
+     it is in register or memory.  */
+  unsigned int base_reg;
+  unsigned int bp_loc;
+  /* If the other register is stashed on stack, note the offset.  */
+  offsetT bp_offset;
+
+  /* Track RA location.  Specify whether it is in register or memory.  */
+  unsigned int ra_loc;
+  /* If RA is stashed on stack, note the offset.  */
+  offsetT ra_offset;
+};
+
+/* SFrame Function Description Entry.  */
+
+struct sframe_func_entry
+{
+  /* A linked list.  */
+  struct sframe_func_entry *next;
+
+  /* Reference to the FDE created from CFI in dw2gencfi.  Some information
+     like the start_address and the segment is made available via this
+     member.  */
+  const struct fde_entry *dw_fde;
+
+  /* Reference to the first FRE for this function.  */
+  struct sframe_row_entry *sframe_fres;
+
+  unsigned int num_fres;
+};
+
+/* SFrame Function Description Entry Translation Context.  */
+
+struct sframe_xlate_ctx
+{
+  /* Reference to the FDE created from CFI in dw2gencfi.  Information
+     like the FDE start_address, end_address and the cfi insns are
+     made available via this member.  */
+  const struct fde_entry *dw_fde;
+
+  /* List of FREs in the current FDE translation context, bounded by first_fre
+     and last_fre.  */
+
+  /* Keep track of the first FRE for the purpose of restoring state if
+     necessary (for DW_CFA_restore).  */
+  struct sframe_row_entry *first_fre;
+  /* The last FRE in the list.  */
+  struct sframe_row_entry *last_fre;
+
+  /* The current FRE under construction.  */
+  struct sframe_row_entry *cur_fre;
+  /* Remember FRE for an eventual restore.  */
+  struct sframe_row_entry *remember_fre;
+
+  unsigned num_xlate_fres;
+};
+
+/* Error codes for SFrame translation context.  */
+enum sframe_xlate_err
+{
+  /* Success.  */
+  SFRAME_XLATE_OK = 0,
+  /* Error.  */
+  SFRAME_XLATE_ERROR = 1,
+  /* Detailed error codes.  */
+  SFRAME_XLATE_ERR_INVAL = -1,
+  SFRAME_XLATE_ERR_NOTREPRESENTED = -2,
+};
+
+/* Callback to create the abi/arch identifier for SFrame section.  */
+
+unsigned char
+sframe_get_abi_arch_callback (const char *target_arch,
+			      int big_endian_p);
+
+/* The list of all FDEs with data in SFrame internal representation.  */
+
+extern struct sframe_func_entry *all_sframe_fdes;
+
+/* SFrame version specific operations structure.  */
+
+struct sframe_version_ops
+{
+  unsigned char format_version;    /* SFrame format version.  */
+  /* set SFrame FRE info.  */
+  unsigned char (*set_fre_info) (unsigned int, unsigned int, unsigned int);
+  /* set SFrame Func info.  */
+  unsigned char (*set_func_info) (unsigned int, unsigned int);
+};
+
+/* Generate SFrame unwind info and prepare contents for the output.
+   outout_sframe ()  is called at the end of file.  */
+
+extern void output_sframe (segT sframe_seg);
+
+#endif /* GENSFRAME_H */
diff --git a/gas/sframe-opt.c b/gas/sframe-opt.c
new file mode 100644
index 0000000..c17fd6b
--- /dev/null
+++ b/gas/sframe-opt.c
@@ -0,0 +1,158 @@
+/* sframe-opt.c - optimize FRE and FDE information in SFrame.
+   Copyright (C) 2022 Free Software Foundation, Inc.
+
+   This file is part of GAS, the GNU Assembler.
+
+   GAS is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3, or (at your option)
+   any later version.
+
+   GAS is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with GAS; see the file COPYING.  If not, write to the Free
+   Software Foundation, 51 Franklin Street - Fifth Floor, Boston, MA
+   02110-1301, USA.  */
+
+#include "as.h"
+#include "sframe.h"
+
+/* The function estimates the size of a rs_sframe variant frag based on
+   the current values of the symbols.  It is called before the
+   relaxation loop.  We set fr_subtype{0:2} to the expected length.  */
+
+int
+sframe_estimate_size_before_relax (fragS *frag)
+{
+  offsetT width;
+  expressionS *exp;
+  symbolS *widthS;
+  int ret;
+
+  /* We are dealing with two different kind of fragments here which need
+     to be fixed up:
+       - first, FRE start address in each FRE, and
+       - second, Function info in each FDE (function info stores the FRE type)
+     The two kind of fragments can be differentiated based on the opcode
+     of the symbol.  */
+  exp = symbol_get_value_expression (frag->fr_symbol);
+  gas_assert ((exp->X_op == O_subtract) || (exp->X_op == O_absent));
+  /* Fragment for function info in an SFrame FDE will always write
+     only one byte.  */
+  if (exp->X_op == O_subtract)
+    ret = 1;
+  /* Fragment for the start address in an SFrame FRE may write out
+     1/2/4 bytes depending on the value of the diff.  */
+  else
+    {
+      /* Get the width expression from the symbol.  */
+      widthS = exp->X_op_symbol;
+      width = resolve_symbol_value (widthS);
+
+      if (width < 0x100)
+	ret = 1;
+      else if (width < 0x10000)
+	ret = 2;
+      else
+	ret = 4;
+    }
+
+  frag->fr_subtype = (frag->fr_subtype & ~7) | (ret & 7);
+
+  return ret;
+}
+
+/* This function relaxes a rs_sframe variant frag based on the current
+   values of the symbols.  fr_subtype{0:2} is the current length of
+   the frag.  This returns the change in frag length.  */
+
+int
+sframe_relax_frag (fragS *frag)
+{
+  int oldsize, newsize;
+
+  oldsize = frag->fr_subtype & 7;
+  if (oldsize == 7)
+    oldsize = -1;
+  newsize = sframe_estimate_size_before_relax (frag);
+  return newsize - oldsize;
+}
+
+/* This function converts a rs_sframe variant frag into a normal fill
+   frag.  This is called after all relaxation has been done.
+   fr_subtype{0:2} will be the desired length of the frag.  */
+
+void
+sframe_convert_frag (fragS *frag)
+{
+  offsetT fsize;
+  offsetT diff;
+  offsetT value;
+  unsigned char func_info = SFRAME_FRE_TYPE_ADDR4;
+  expressionS *exp;
+  symbolS *fsizeS, *diffS;
+
+  /* We are dealing with two different kind of fragments here which need
+     to be fixed up:
+       - first, FRE start address in each FRE, and
+       - second, Function info in each FDE (function info stores the FRE type)
+     The two kind of fragments can be differentiated based on the opcode
+     of the symbol.  */
+  exp = symbol_get_value_expression (frag->fr_symbol);
+  gas_assert ((exp->X_op == O_subtract) || (exp->X_op == O_absent));
+  /* Fragment for function info in an SFrame FDE.  */
+  if (exp->X_op == O_subtract)
+    {
+      fsizeS = frag->fr_symbol;
+      fsize = resolve_symbol_value (fsizeS);
+      if (fsize < 0x100)
+	func_info = SFRAME_FRE_TYPE_ADDR1;
+      else if (fsize < 0x10000)
+	func_info = SFRAME_FRE_TYPE_ADDR2;
+      else
+	func_info = SFRAME_FRE_TYPE_ADDR4;
+      value = func_info;
+
+      frag->fr_literal[frag->fr_fix] = value;
+    }
+  /* Fragment for the start address in an SFrame FRE.  */
+  else
+    {
+      /* Get the fsize expression from the symbol.  */
+      fsizeS = exp->X_op_symbol;
+      fsize = resolve_symbol_value (fsizeS);
+      /* Get the diff expression from the symbol.  */
+      diffS= exp->X_add_symbol;
+      diff = resolve_symbol_value (diffS);
+      value = diff;
+
+      switch (frag->fr_subtype & 7)
+	{
+	case 1:
+	  gas_assert (fsize < 0x100);
+	  frag->fr_literal[frag->fr_fix] = diff;
+	  break;
+	case 2:
+	  gas_assert (fsize < 0x10000);
+	  md_number_to_chars (frag->fr_literal + frag->fr_fix, diff, 2);
+	  break;
+	case 4:
+	  md_number_to_chars (frag->fr_literal + frag->fr_fix, diff, 4);
+	  break;
+	default:
+	  abort ();
+	}
+    }
+
+  frag->fr_fix += frag->fr_subtype & 7;
+  frag->fr_type = rs_fill;
+  frag->fr_subtype = 0;
+  frag->fr_offset = 0;
+  /* FIXME do this now because we have evaluated and fixed up the fragments
+     manually ?  */
+  frag->fr_symbol = 0;
+}
diff --git a/gas/write.c b/gas/write.c
index 3014f68..fa748eb 100644
--- a/gas/write.c
+++ b/gas/write.c
@@ -487,6 +487,10 @@ cvt_frag_to_fill (segT sec ATTRIBUTE_UNUSED, fragS *fragP)
       dwarf2dbg_convert_frag (fragP);
       break;
 
+    case rs_sframe:
+      sframe_convert_frag (fragP);
+      break;
+
     case rs_machine_dependent:
       md_convert_frag (stdoutput, sec, fragP);
 
@@ -2781,6 +2785,11 @@ relax_segment (struct frag *segment_frag_root, segT segment, int pass)
 	  address += dwarf2dbg_estimate_size_before_relax (fragP);
 	  break;
 
+	case rs_sframe:
+	  /* Initial estimate can be set to atleast 1 byte.  */
+	  address += sframe_estimate_size_before_relax (fragP);
+	  break;
+
 	default:
 	  BAD_CASE (fragP->fr_type);
 	  break;
@@ -3124,6 +3133,10 @@ relax_segment (struct frag *segment_frag_root, segT segment, int pass)
 		growth = dwarf2dbg_relax_frag (fragP);
 		break;
 
+	      case rs_sframe:
+		growth = sframe_relax_frag (fragP);
+		break;
+
 	      default:
 		BAD_CASE (fragP->fr_type);
 		break;