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.

1 files changed, 40 insertions, 1 deletions

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;