s390: SFrame track FP/RA saved in register

GCC on s390x, when in a leaf function, can be observed to save the
frame pointer (FP) and/or return address (RA) register in a floating-
point registers (FPR) instead of on the stack. This is declared using
the following CFI directive:

  .cfi_register <fp/ra-regno>, <fpr-regno>

SFrame cannot represent the FP and/or RA being saved in another
register. It does only track the CFA base register (SP/FP), CFA offset
from CFA base register, and FP and RA save area offsets from CFA.

On s390x the FP and/or RA are only saved in another FPR when in a leaf
function. That is a function that does not call any other functions.
Therefore it can ever only be the topmost function in a call chain.
During function return, if the RA would be restored into a non-default
RA register, the function would also only ever be the topmost function
on the call stack.
An unwinder by default has access to all registers of the function that
if the topmost on the call stack. Therefore no further information would
be required for those registers.

Represent the FP/RA in another register on s390, by encoding the
register number shifted by one to the left with the least-significant
bit set in the offset as follows:

  offset = (regno << 1) | 1

Add s390-specific SFrame (error) test cases for FP/RA being saved in
FPRs in leaf-function.

gas/
	* gen-sframe.c (s390_sframe_xlate_do_register): New s390-
	specific function to represent FP/RA in another register on
	s390.
	(sframe_xlate_do_register): Invoke s390_sframe_xlate_do_register
	on s390.

libsframe/
	* sframe-dump.c (is_sframe_abi_arch_s390): New helper to test
	whether ABI/arch is s390.
	(dump_sframe_func_with_fres): Dump FP/RA in another register on
	s390.

gas/testsuite/
	* gas/cfi-sframe/cfi-sframe.exp: Update s390-specific SFrame
	(error) test cases.
	* gas/cfi-sframe/cfi-sframe-s390-fpra-register-err-2.s: Rename
	to ...
	* gas/cfi-sframe/cfi-sframe-s390-fpra-register-err-2.d:
	Likewise.
	* gas/cfi-sframe/cfi-sframe-s390-fpra-register-1.s: This. Test
	case no longer triggers a warning, as SFrame can represent FP
	and RA saved in registers.
	* gas/cfi-sframe/cfi-sframe-s390-fpra-register-1.d: Likewise.
	* gas/cfi-sframe/cfi-sframe-s390-fpra-register-err-1.d: Test
	case now triggers a different warning, as SFrame can represent
	FP and RA saved in registers, but not FP without RA saved in
	register.

Signed-off-by: Jens Remus <jremus@linux.ibm.com>

7 files changed, 80 insertions, 20 deletions

diff --git a/gas/gen-sframe.c b/gas/gen-sframe.c
index dd97d4f..0bb7afb 100644
--- a/gas/gen-sframe.c
+++ b/gas/gen-sframe.c
@@ -1152,6 +1152,37 @@ sframe_xlate_do_val_offset (struct sframe_xlate_ctx *xlate_ctx ATTRIBUTE_UNUSED,
   return SFRAME_XLATE_OK;
 }
 
+/* S390-specific translate DW_CFA_register into SFrame context.
+   Return SFRAME_XLATE_OK if success.  */
+
+static int
+s390_sframe_xlate_do_register (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 register.  Encode the register number as offset by
+     shifting it to the left by one and setting the least-significant bit
+     (LSB).  The LSB can be used to differentiate offsets from register
+     numbers, as offsets from CFA are always a multiple of -8 on s390x.  */
+  if (cfi_insn->u.rr.reg1 == SFRAME_CFA_FP_REG)
+    sframe_fre_set_bp_track (cur_fre, cfi_insn->u.rr.reg2 << 1 | 1);
+#ifdef SFRAME_FRE_RA_TRACKING
+  else if (sframe_ra_tracking_p ()
+	   && cfi_insn->u.rr.reg1 == SFRAME_CFA_RA_REG)
+    sframe_fre_set_ra_track (cur_fre, cfi_insn->u.rr.reg2 << 1 | 1);
+#endif
+
+  /* Safe to skip.  */
+  return SFRAME_XLATE_OK;
+}
+
 /* Translate DW_CFA_register into SFrame context.
    Return SFRAME_XLATE_OK if success.  */
 
@@ -1159,6 +1190,10 @@ static int
 sframe_xlate_do_register (struct sframe_xlate_ctx *xlate_ctx ATTRIBUTE_UNUSED,
 			  struct cfi_insn_data *cfi_insn)
 {
+  /* Conditionally invoke S390-specific implementation.  */
+  if (sframe_get_abi_arch () == SFRAME_ABI_S390_ENDIAN_BIG)
+    return s390_sframe_xlate_do_register (xlate_ctx, cfi_insn);
+
   /* Previous value of register1 is register2.  However, if the specified
      register1 is not interesting (FP or RA reg), the current DW_CFA_register
      instruction can be safely skipped without sacrificing the asynchronicity of
diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-fpra-register-1.d b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-fpra-register-1.d
new file mode 100644
index 0000000..7368698
--- /dev/null
+++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-fpra-register-1.d
@@ -0,0 +1,22 @@
+#objdump: --sframe=.sframe
+#name: SFrame generation on s390 - FP and RA registers saved in FPR registers
+#...
+Contents of the SFrame section .sframe:
+
+  Header :
+
+    Version: SFRAME_VERSION_2
+    Flags: NONE
+    Num FDEs: 1
+    Num FREs: 5
+
+  Function Index :
+
+    func idx \[0\]: pc = 0x0, size = 26 bytes
+    STARTPC +CFA +FP +RA +
+    0+0000 +sp\+160 +u +u +
+    0+0004 +sp\+160 +u +r16 +
+    0+0008 +sp\+160 +r17 +r16 +
+    0+0014 +sp\+160 +u +r16 +
+    0+0018 +sp\+160 +u +u +
+#pass
diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-fpra-register-err-2.s b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-fpra-register-1.s
index 1d44971..1d44971 100644
--- a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-fpra-register-err-2.s
+++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-fpra-register-1.s
diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-fpra-register-err-1.d b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-fpra-register-err-1.d
index 2b9456b..49d4e4a 100644
--- a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-fpra-register-err-1.d
+++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-fpra-register-err-1.d
@@ -1,6 +1,6 @@
-#name: SFrame generation on s390 - FP and RA saved in register
+#name: SFrame generation on s390 - FP without RA saved in register
 #as: --gsframe
-#warning: skipping SFrame FDE due to .cfi_register specifying FP register
+#warning: skipping SFrame FDE due to FP without RA on stack
 #objdump: --sframe=.sframe
 #...
 Contents of the SFrame section .sframe:
diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-fpra-register-err-2.d b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-fpra-register-err-2.d
deleted file mode 100644
index 4c15bd0..0000000
--- a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-fpra-register-err-2.d
+++ /dev/null
@@ -1,15 +0,0 @@
-#name: SFrame generation on s390 - FP and RA saved in register
-#as: --gsframe
-#warning: skipping SFrame FDE due to .cfi_register specifying RA register
-#objdump: --sframe=.sframe
-#...
-Contents of the SFrame section .sframe:
-
-  Header :
-
-    Version: SFRAME_VERSION_2
-    Flags: NONE
-    Num FDEs: 0
-    Num FREs: 0
-
-#pass
diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe.exp b/gas/testsuite/gas/cfi-sframe/cfi-sframe.exp
index 67735d4..77281a1 100644
--- a/gas/testsuite/gas/cfi-sframe/cfi-sframe.exp
+++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe.exp
@@ -110,6 +110,6 @@ if { [istarget "s390x*-*-*"] && [gas_sframe_check] } then {
     run_dump_test "cfi-sframe-s390-err-3"
     run_dump_test "cfi-sframe-s390-fpra-offset-1"
     run_dump_test "cfi-sframe-s390-fpra-offset-err-1"
+    run_dump_test "cfi-sframe-s390-fpra-register-1"
     run_dump_test "cfi-sframe-s390-fpra-register-err-1"
-    run_dump_test "cfi-sframe-s390-fpra-register-err-2"
 }
diff --git a/libsframe/sframe-dump.c b/libsframe/sframe-dump.c
index 69633d5..40ea531 100644
--- a/libsframe/sframe-dump.c
+++ b/libsframe/sframe-dump.c
@@ -40,6 +40,14 @@ is_sframe_abi_arch_aarch64 (sframe_decoder_ctx *sfd_ctx)
   return aarch64_p;
 }
 
+/* Return TRUE if the SFrame section is associated with the s390 ABIs.  */
+
+static bool
+is_sframe_abi_arch_s390 (sframe_decoder_ctx *sfd_ctx)
+{
+  return sframe_decoder_get_abi_arch (sfd_ctx) == SFRAME_ABI_S390_ENDIAN_BIG;
+}
+
 static void
 dump_sframe_header (sframe_decoder_ctx *sfd_ctx)
 {
@@ -175,7 +183,12 @@ dump_sframe_func_with_fres (sframe_decoder_ctx *sfd_ctx,
 
       /* Dump SP/FP info.  */
       if (err[1] == 0)
-	sprintf (temp, "c%+d", fp_offset);
+	{
+	  if (is_sframe_abi_arch_s390 (sfd_ctx) && (fp_offset & 1))
+	    sprintf (temp, "r%d", fp_offset >> 1);
+	  else
+	    sprintf (temp, "c%+d", fp_offset);
+	}
       else
 	strcpy (temp, "u");
       printf ("%-10s", temp);
@@ -187,7 +200,12 @@ dump_sframe_func_with_fres (sframe_decoder_ctx *sfd_ctx,
 	  != SFRAME_CFA_FIXED_RA_INVALID)
 	strcpy (temp, "f");
       else if (err[2] == 0)
-	sprintf (temp, "c%+d", ra_offset);
+	{
+	  if (is_sframe_abi_arch_s390 (sfd_ctx) && (ra_offset & 1))
+	    sprintf (temp, "r%d", ra_offset >> 1);
+	  else
+	    sprintf (temp, "c%+d", ra_offset);
+	}
       else
 	strcpy (temp, "u");