[PATCH] New option --print-gc-sections

[Eric Botcazou <ebotcazou at adacore dot com>]

Hi,

We'd like to introduce a --print-gc-sections option, to be used in conjunction 
with --gc-sections, now that its output is accurate thanks to HJ's work.

The warning/error message format recently changed and is now one-lined, so I'm 
proposing the following format:

1. "objfile:location GC function" for .text.function sections.
2. "objfile GC section" for other sections.

For example, on an Ada example with --print-gc-sections --demangle=gnat:

./u.o GC .text
./u.o GC .bss
./u.o:/home/eric/gnat/bugs/F115-010/u.adb:18 GC u.unused
./u.o GC .gcc_except_table.u__unused
./u.o:/home/eric/gnat/bugs/F115-010/u.adb:27 GC u.unused_2
./ma.o GC .text
./ma.o GC .data
./ma.o GC .bss

Tentative patch attached, tested on AMD64/Linux.  Comments?


2006-03-28  Eric Botcazou  <ebotcazou@adacore.com>

bfd/
	* elflink.c (elf_gc_sweep): Invoke the gc_section link callback
	on excluded sections.

include/
	* bfdlink.h (struct bfd_link_info): New flag print_gc_sections.
	(struct bfd_link_callbacks): New method gc_section.

ld/
	* ld.texinfo (Command Line Options): Document --print-gc-sections.
	* ldmain.c (gc_section): New callback.
	(link_callbacks): Add gc_section.
	* lexsup.c (enum option_values): New value OPTION_PRINT_GC_SECTIONS.
	(ld_options): Add --print-gc-sections.
	(parse_args): Handle OPTION_PRINT_GC_SECTIONS.


-- 
Eric Botcazou

Index: bfd/elflink.c
===================================================================
RCS file: /cvs/src/src/bfd/elflink.c,v
retrieving revision 1.207
diff -u -p -r1.207 elflink.c
--- bfd/elflink.c	17 Mar 2006 18:37:21 -0000	1.207
+++ bfd/elflink.c	28 Mar 2006 09:06:30 -0000
@@ -8930,6 +8930,9 @@ elf_gc_sweep (bfd *abfd, struct bfd_link
 	     to remove a section from the output.  */
 	  o->flags |= SEC_EXCLUDE;
 
+	  if (! (*info->callbacks->gc_section) (info, sub, o))
+	    return FALSE;
+
 	  /* But we also have to update some of the relocation
 	     info we collected before.  */
 	  if (gc_sweep_hook
Index: include/bfdlink.h
===================================================================
RCS file: /cvs/src/src/include/bfdlink.h,v
retrieving revision 1.58
diff -u -p -r1.58 bfdlink.h
--- include/bfdlink.h	3 Nov 2005 02:52:51 -0000	1.58
+++ include/bfdlink.h	28 Mar 2006 09:06:30 -0000
@@ -327,6 +327,9 @@ struct bfd_link_info
   /* TRUE if unreferenced sections should be removed.  */
   unsigned int gc_sections: 1;
 
+  /* TRUE if we should print the list of garbage-collected sections.  */
+  unsigned int print_gc_sections: 1;
+
   /* What to do with unresolved symbols in an object file.
      When producing executables the default is GENERATE_ERROR.
      When producing shared libraries the default is IGNORE.  The
@@ -534,6 +537,10 @@ struct bfd_link_callbacks
   bfd_boolean (*notice)
     (struct bfd_link_info *, const char *name,
      bfd *abfd, asection *section, bfd_vma address);
+ /* A function which is called when a section is garbage-collected.
+    ABFD and SECTION are the section.  */
+  bfd_boolean (*gc_section)
+    (struct bfd_link_info *, bfd *abfd, asection *section);
   /* General link info message.  */
   void (*einfo)
     (const char *fmt, ...);
Index: ld/ld.texinfo
===================================================================
RCS file: /cvs/src/src/ld/ld.texinfo,v
retrieving revision 1.157
diff -u -p -r1.157 ld.texinfo
--- ld/ld.texinfo	3 Mar 2006 09:31:59 -0000	1.157
+++ ld/ld.texinfo	28 Mar 2006 09:06:31 -0000
@@ -1220,6 +1220,11 @@ with @samp{-r}. The default behaviour (o
 collection) can be restored by specifying @samp{--no-gc-sections} on
 the command line.
 
+@kindex --print-gc-sections
+@cindex garbage collection
+@item --print-gc-sections
+Print the list of garbage-collected sections with @samp{--gc-sections}.
+
 @cindex help
 @cindex usage
 @kindex --help
Index: ld/ldmain.c
===================================================================
RCS file: /cvs/src/src/ld/ldmain.c,v
retrieving revision 1.105
diff -u -p -r1.105 ldmain.c
--- ld/ldmain.c	16 Mar 2006 12:20:16 -0000	1.105
+++ ld/ldmain.c	28 Mar 2006 09:06:31 -0000
@@ -147,6 +147,8 @@ static bfd_boolean unattached_reloc
   (struct bfd_link_info *, const char *, bfd *, asection *, bfd_vma);
 static bfd_boolean notice
   (struct bfd_link_info *, const char *, bfd *, asection *, bfd_vma);
+static bfd_boolean gc_section
+  (struct bfd_link_info *, bfd *, asection *);
 
 static struct bfd_link_callbacks link_callbacks =
 {
@@ -161,6 +163,7 @@ static struct bfd_link_callbacks link_ca
   reloc_dangerous,
   unattached_reloc,
   notice,
+  gc_section,
   einfo
 };
 
@@ -316,6 +319,7 @@ main (int argc, char **argv)
   link_info.need_relax_finalize = FALSE;
   link_info.warn_shared_textrel = FALSE;
   link_info.gc_sections = FALSE;
+  link_info.print_gc_sections = FALSE;
 
   ldfile_add_arch ("");
 
@@ -1526,3 +1530,22 @@ notice (struct bfd_link_info *info,
 
   return TRUE;
 }
+
+/* This is called when a section is garbage-collected.  */
+
+static bfd_boolean
+gc_section (struct bfd_link_info *info,
+	    bfd *abfd,
+	    asection *section)
+{
+  if (! info->print_gc_sections)
+    return TRUE;
+
+  if (strncmp (section->name, ".text.", 6) == 0)
+    einfo ("%D GC %s\n", abfd, section, (bfd_vma) 0,
+	   demangle (section->name+6));
+  else
+    einfo ("%B GC %A\n", abfd, section);
+
+  return TRUE;
+}
Index: ld/lexsup.c
===================================================================
RCS file: /cvs/src/src/ld/lexsup.c,v
retrieving revision 1.87
diff -u -p -r1.87 lexsup.c
--- ld/lexsup.c	30 Oct 2005 18:08:52 -0000	1.87
+++ ld/lexsup.c	28 Mar 2006 09:06:31 -0000
@@ -124,6 +124,7 @@ enum option_values
   OPTION_FORCE_EXE_SUFFIX,
   OPTION_GC_SECTIONS,
   OPTION_NO_GC_SECTIONS,
+  OPTION_PRINT_GC_SECTIONS,
   OPTION_HASH_SIZE,
   OPTION_CHECK_SECTIONS,
   OPTION_NO_CHECK_SECTIONS,
@@ -421,6 +422,8 @@ static const struct ld_option ld_options
   { {"oformat", required_argument, NULL, OPTION_OFORMAT},
     '\0', N_("TARGET"), N_("Specify target of output file"),
     EXACTLY_TWO_DASHES },
+  { {"print-gc-sections", no_argument, NULL, OPTION_PRINT_GC_SECTIONS},
+    '\0', NULL, N_("Print garbage-collected sections"), TWO_DASHES },
   { {"qmagic", no_argument, NULL, OPTION_IGNORE},
     '\0', NULL, N_("Ignored for Linux compatibility"), ONE_DASH },
   { {"reduce-memory-overheads", no_argument, NULL,
@@ -952,6 +955,9 @@ parse_args (unsigned argc, char **argv)
 	case OPTION_OFORMAT:
 	  lang_add_output_format (optarg, NULL, NULL, 0);
 	  break;
+	case OPTION_PRINT_GC_SECTIONS:
+	  link_info.print_gc_sections = TRUE;
+	  break;
 	case 'q':
 	  link_info.emitrelocations = TRUE;
 	  break;