gas: allow labeling of CFI instructions

When runtime patching code (like e.g. done by the Linux kernel) there
may be cases where the set of stack frame alterations differs between
unpatched and patched code. Consequently the corresponding unwind data
needs patching too. Locating the right places within an FDE, however,
is rather cumbersome without a way to insert labels in the resulting
section. Hence this patch introduces a new directive, .cfi_label. Note
that with the way CFI data gets emitted currently (at the end of the
assembly process) this can't support local FB- and dollar-labels.

gas/
2015-01-12  Jan Beulich  <jbeulich@suse.com>

	* gas/dw2gencfi.c (cfi_add_label, dot_cfi_label): New.
	(cfi_pseudo_table): Add "cfi_label".
	(output_cfi_insn): Handle CFI_label.
	(select_cie_for_fde): Als terminate CIE when encountering
	CFI_label.
	* dw2gencfi.h (cfi_add_label): Declare.
	(struct cfi_insn_data): New member "sym_name".
	(CFI_label): New.
	* read.c (read_symbol_name): Drop "static".
	* read.h (read_symbol_name): Declare.

gas/testsuite/
2015-01-12  Jan Beulich  <jbeulich@suse.com>

	gas/cfi/cfi-label.d, gas/cfi/cfi-label.s: New.
	gas/cfi/cfi.exp: Run new tests.

9 files changed, 130 insertions, 2 deletions

diff --git a/gas/ChangeLog b/gas/ChangeLog
index 2e3b2e9..78501ed 100644
--- a/gas/ChangeLog
+++ b/gas/ChangeLog
@@ -1,5 +1,18 @@
 2015-01-12  Jan Beulich  <jbeulich@suse.com>
 
+	* gas/dw2gencfi.c (cfi_add_label, dot_cfi_label): New.
+	(cfi_pseudo_table): Add "cfi_label".
+	(output_cfi_insn): Handle CFI_label.
+	(select_cie_for_fde): Als terminate CIE when encountering
+	CFI_label.
+	* dw2gencfi.h (cfi_add_label): Declare.
+	(struct cfi_insn_data): New member "sym_name".
+	(CFI_label): New.
+	* read.c (read_symbol_name): Drop "static".
+	* read.h (read_symbol_name): Declare.
+
+2015-01-12  Jan Beulich  <jbeulich@suse.com>
+
 	* gas/config/tc-arm.c (do_neon_shl_imm): Check immediate range.
 	(do_neon_qshl_imm): Likewise.
 
diff --git a/gas/dw2gencfi.c b/gas/dw2gencfi.c
index 939c41a..6a80d0b 100644
--- a/gas/dw2gencfi.c
+++ b/gas/dw2gencfi.c
@@ -440,6 +440,19 @@ cfi_add_advance_loc (symbolS *label)
   frchain_now->frch_cfi_data->last_address = label;
 }
 
+/* Add a CFI insn to label the current position in the CFI segment.  */
+
+void
+cfi_add_label (const char *name)
+{
+  unsigned int len = strlen (name) + 1;
+  struct cfi_insn_data *insn = alloc_cfi_insn_data ();
+
+  insn->insn = CFI_label;
+  obstack_grow (&notes, name, len);
+  insn->u.sym_name = (char *) obstack_finish (&notes);
+}
+
 /* Add a DW_CFA_offset record to the CFI data.  */
 
 void
@@ -550,6 +563,7 @@ static void dot_cfi_endproc (int);
 static void dot_cfi_personality (int);
 static void dot_cfi_lsda (int);
 static void dot_cfi_val_encoded_addr (int);
+static void dot_cfi_label (int);
 
 const pseudo_typeS cfi_pseudo_table[] =
   {
@@ -575,6 +589,7 @@ const pseudo_typeS cfi_pseudo_table[] =
     { "cfi_personality", dot_cfi_personality, 0 },
     { "cfi_lsda", dot_cfi_lsda, 0 },
     { "cfi_val_encoded_addr", dot_cfi_val_encoded_addr, 0 },
+    { "cfi_label", dot_cfi_label, 0 },
     { NULL, NULL, 0 }
   };
 
@@ -1016,6 +1031,25 @@ dot_cfi_val_encoded_addr (int ignored ATTRIBUTE_UNUSED)
   demand_empty_rest_of_line ();
 }
 
+static void
+dot_cfi_label (int ignored ATTRIBUTE_UNUSED)
+{
+  char *name = read_symbol_name ();
+
+  if (name == NULL)
+    return;
+
+  /* If the last address was not at the current PC, advance to current.  */
+  if (symbol_get_frag (frchain_now->frch_cfi_data->last_address) != frag_now
+      || S_GET_VALUE (frchain_now->frch_cfi_data->last_address)
+	 != frag_now_fix ())
+    cfi_add_advance_loc (symbol_temp_new_now ());
+
+  cfi_add_label (name);
+
+  demand_empty_rest_of_line ();
+}
+
 /* By default emit .eh_frame only, not .debug_frame.  */
 #define CFI_EMIT_eh_frame	(1 << 0)
 #define CFI_EMIT_debug_frame	(1 << 1)
@@ -1386,6 +1420,10 @@ output_cfi_insn (struct cfi_insn_data *insn)
       }
       break;
 
+    case CFI_label:
+      colon (insn->u.sym_name);
+      break;
+
     default:
       abort ();
     }
@@ -1761,7 +1799,8 @@ select_cie_for_fde (struct fde_entry *fde, bfd_boolean eh_frame,
     if (i->insn == DW_CFA_advance_loc
 	|| i->insn == DW_CFA_remember_state
 	|| i->insn == CFI_escape
-	|| i->insn == CFI_val_encoded_addr)
+	|| i->insn == CFI_val_encoded_addr
+	|| i->insn == CFI_label)
       break;
 
   cie->last = i;
diff --git a/gas/dw2gencfi.h b/gas/dw2gencfi.h
index e80b19e..6e2c50e 100644
--- a/gas/dw2gencfi.h
+++ b/gas/dw2gencfi.h
@@ -37,6 +37,7 @@ extern void cfi_new_fde (struct symbol *);
 extern void cfi_end_fde (struct symbol *);
 extern void cfi_set_return_column (unsigned);
 extern void cfi_add_advance_loc (struct symbol *);
+extern void cfi_add_label (const char *);
 
 extern void cfi_add_CFA_offset (unsigned, offsetT);
 extern void cfi_add_CFA_def_cfa (unsigned, offsetT);
@@ -94,6 +95,8 @@ struct cfi_insn_data
       unsigned reg, encoding;
       expressionS exp;
     } ea;
+
+    const char *sym_name;
   } u;
 };
 
@@ -128,5 +131,6 @@ extern struct fde_entry *all_fde_data;
 #define CFI_escape		0x103
 #define CFI_signal_frame	0x104
 #define CFI_val_encoded_addr	0x105
+#define CFI_label		0x106
 
 #endif /* DW2GENCFI_H */
diff --git a/gas/read.c b/gas/read.c
index 7dfc20a..b2d5027 100644
--- a/gas/read.c
+++ b/gas/read.c
@@ -1600,7 +1600,7 @@ s_altmacro (int on)
    If a symbol name could not be read, the routine issues an error
    messages, skips to the end of the line and returns NULL.  */
 
-static char *
+char *
 read_symbol_name (void)
 {
   char * name;
diff --git a/gas/read.h b/gas/read.h
index 32d3767..d7ac6ce 100644
--- a/gas/read.h
+++ b/gas/read.h
@@ -127,6 +127,7 @@ extern void pseudo_set (symbolS * symbolP);
 extern void read_a_source_file (char *name);
 extern void read_begin (void);
 extern void read_print_statistics (FILE *);
+extern char *read_symbol_name (void);
 extern int sizeof_leb128 (valueT, int sign);
 extern void stabs_generate_asm_file (void);
 extern void stabs_generate_asm_lineno (void);
diff --git a/gas/testsuite/ChangeLog b/gas/testsuite/ChangeLog
index ef359a1..54d9c6e 100644
--- a/gas/testsuite/ChangeLog
+++ b/gas/testsuite/ChangeLog
@@ -1,5 +1,10 @@
 2015-01-12  Jan Beulich  <jbeulich@suse.com>
 
+	gas/cfi/cfi-label.d, gas/cfi/cfi-label.s: New.
+	gas/cfi/cfi.exp: Run new tests.
+
+2015-01-12  Jan Beulich  <jbeulich@suse.com>
+
 	* gas/arm/neon-addressing-bad.s: Add test for invalid VSHL,
 	VQSHL, and VQSHLU immediates.
 	* gas/arm/neon-addressing-bad.l: Update accordingly. 
diff --git a/gas/testsuite/gas/cfi/cfi-label.d b/gas/testsuite/gas/cfi/cfi-label.d
new file mode 100644
index 0000000..e96c795
--- /dev/null
+++ b/gas/testsuite/gas/cfi/cfi-label.d
@@ -0,0 +1,43 @@
+#objdump: -tWf
+#name: .cfi_label directive
+
+.*\.o:     file format elf.*
+
+SYMBOL TABLE:
+0*00 l    d  \.text	0*00 \.text
+0*00 l    d  \.data	0*00 \.data
+0*00 l    d  \.bss	0*00 \.bss
+0*00 l     F \.text	0*04 cfilabel
+0*2f l       \.eh_frame	0*00 cfi2
+0*00 l    d  \.eh_frame	0*00 \.eh_frame
+0*2b g       \.eh_frame	0*00 cfi1
+
+
+Contents of the .eh_frame section:
+
+0*00 0*14 0*00 CIE
+  Version:               1
+  Augmentation:          "zR"
+  Code alignment factor: 1
+  Data alignment factor: -[48]
+  Return address column: (8|16)
+  Augmentation data:     1b
+
+  DW_CFA_def_cfa: r.* \([er]sp\) ofs [48]
+  DW_CFA_offset: r.* \([er]ip\) at cfa-[48]
+  DW_CFA_nop
+  DW_CFA_nop
+
+0*18 0*1[8c] 0*1c FDE cie=0*00 pc=0*00..0*04
+  DW_CFA_remember_state
+  DW_CFA_advance_loc: 1 to 0*01
+  DW_CFA_nop
+  DW_CFA_nop
+  DW_CFA_nop
+  DW_CFA_advance_loc: 1 to 0*02
+  DW_CFA_nop
+  DW_CFA_nop
+  DW_CFA_advance_loc: 1 to 0*03
+  DW_CFA_nop
+  DW_CFA_restore_state
+#pass
diff --git a/gas/testsuite/gas/cfi/cfi-label.s b/gas/testsuite/gas/cfi/cfi-label.s
new file mode 100644
index 0000000..f0297ab
--- /dev/null
+++ b/gas/testsuite/gas/cfi/cfi-label.s
@@ -0,0 +1,19 @@
+	.text
+cfilabel:
+	.cfi_startproc
+	.cfi_remember_state
+	nop
+	.globl cfi1
+	.cfi_label cfi1
+	.cfi_escape 0, 0, 0
+	nop
+	.cfi_label cfi2
+	.cfi_escape 0, 0
+	nop
+	.cfi_label .Lcfi3
+	.cfi_escape 0
+	.cfi_restore_state
+	ret
+	.cfi_endproc
+	.type cfilabel, STT_FUNC
+	.size cfilabel, . - cfilabel
diff --git a/gas/testsuite/gas/cfi/cfi.exp b/gas/testsuite/gas/cfi/cfi.exp
index 33ae13e..be84941 100644
--- a/gas/testsuite/gas/cfi/cfi.exp
+++ b/gas/testsuite/gas/cfi/cfi.exp
@@ -51,6 +51,10 @@ if  { [istarget "i*86-*-*"] || [istarget "x86_64-*-*"] } then {
 	set ASFLAGS "$old_ASFLAGS"
     }
 
+    if { [is_elf_format] } then {
+	run_dump_test "cfi-label"
+    }
+
     if { [is_pecoff_format] } then {
 	run_dump_test "reloc-pe-i386"
     }