[PATCH] restore NOSTRIP for .debug_frame on mips-irix

[Olivier Hainque]

Hello,

GCC used to set NOSTRIP bit on .debug_frame and doesn't any more.

This is causing troubles when using the libexc system library e.g.
for frame unwinding purposes, because it expects a single .debug_frame
per executable, the section has NOSTRIP set in system objects and the
native linker doesn't merge those having the bit set together with
those not having it.

Typically, for

   << /* t.c */
      #include <libexc.h>

      int main (void)
      {
	trace_back_stack_and_print ();
	return 0;
      }
   >>

We see

   $ gcc -o t t.c -lexc

   $ elfdump -hv t | grep -A 1 debug_frame
   [37]   SHT_MIPS_DWARF      0          0x9bc0     0x4b0       .debug_frame
	  0          0        0x4        0          0x00000000
   --
   [39]   SHT_MIPS_DWARF      0          0xa5a6     0xa4        .debug_frame
	  0          0        0x1        0          0x08000000 NOSTRIP

   $ ./t
   libexc(158601884): FATAL ERROR update_obj_info: dwarf_elf_init failed
   for ./t -- (107) DW_DLE_DEBUG_FRAME_DUPLICATE  Only one .debug_frame
   section is allowed

The attached patch addresses this by overriding the default elf
asm_named_section implementation on irix for ".debug_frame" only, to
special case it in a similar fashion as before.

Proper behavior with GNU as requires a change there as well to
propagate the flags down into the object, but this is a separate
issue.

Bootstrapped and regression tested for languages=c,c++,ada on
mips-sgi-irix6.5.

Thanks in advance,

Olivier

2007-10-08  Olivier Hainque  <hainque@adacore.com>

	* config/mips/mips.c (irix_asm_named_section): New function.
	Handle .debug_frame specially and fallback to the default elf
	support otherwise.
	* config/mips/iris.h (TARGET_ASM_NAMED_SECTION): Define.



-------------- next part --------------
Index: config/mips/iris.h
===================================================================
*** config/mips/iris.h	(revision 128810)
--- config/mips/iris.h	(working copy)
*************** along with GCC; see the file COPYING3.  
*** 60,65 ****
--- 60,71 ----
  #undef ASM_FINISH_DECLARE_OBJECT
  #define ASM_FINISH_DECLARE_OBJECT mips_finish_declare_object
  
+ /* System libraries like libexc expect mips specific flags to be set
+    on specific sections, such as NOSTRIP on .debug_frame.  The generic
+    elf circuitry doesn't know about them, so ...  */
+ #undef  TARGET_ASM_NAMED_SECTION
+ #define TARGET_ASM_NAMED_SECTION irix_asm_named_section
+ 
  /* The linker needs a space after "-o".  */
  #define SWITCHES_NEED_SPACES "o"
  
Index: config/mips/mips.c
===================================================================
*** config/mips/mips.c	(revision 128810)
--- config/mips/mips.c	(working copy)
*************** static void mips_output_mi_thunk (FILE *
*** 344,349 ****
--- 344,350 ----
  static section *mips_select_rtx_section (enum machine_mode, rtx,
  					 unsigned HOST_WIDE_INT);
  static section *mips_function_rodata_section (tree);
+ static void irix_asm_named_section (const char *, unsigned int, tree);
  static bool mips_in_small_data_p (const_tree);
  static bool mips_use_anchors_for_symbol_p (const_rtx);
  static int mips_fpr_return_fields (const_tree, tree *);
*************** mips_function_rodata_section (tree decl)
*** 9035,9040 ****
--- 9036,9074 ----
    return data_section;
  }
  
+ /* Implement TARGET_ASM_NAMED_SECTION.  Some sections need special bits
+    that the generic elf circuitry doesn't know about.  Handle them specially
+    here and fallback on the default code for the others.  */
+ 
+ #define SHF_MIPS_NOSTRIP 0x08000000
+ #define SHT_MIPS_DWARF   0x7000001e
+ 
+ static void
+ irix_asm_named_section (const char *name, unsigned int flags, tree decl)
+ {
+   unsigned int sh_type = 0, sh_flags = 0, sh_entsize = 0, sh_align = 0;
+   bool need_special_flags = false;
+ 
+   /* System libraries like libexc expect a single .debug_frame per
+      executable.  The section has NOSTRIP set in system objects and
+      the linker doesn't merge those having the bit set together with
+      those not having it, so make sure we set it as well.  */
+ 
+   if (strcmp (name, ".debug_frame") == 0)
+     {
+       need_special_flags = true;
+       sh_type = SHT_MIPS_DWARF;
+       sh_flags = SHF_MIPS_NOSTRIP;
+       sh_align = 4;
+     }
+ 
+   if (need_special_flags)
+     fprintf (asm_out_file, "\t.section %s,%#x,%#x,%u,%u\n",
+            name, sh_type, sh_flags, sh_entsize, sh_align);
+   else
+     default_elf_asm_named_section (name, flags, decl);
+ }
+