Commit: Skip generating GNU Build notes for linkonce sections

Message ID 87vabqmhpm.fsf@redhat.com
State New
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Series
  • Commit: Skip generating GNU Build notes for linkonce sections
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Commit Message

Nick Clifton May 14, 2018, 2:31 p.m.
Hi Guys,

  I am applying the attached patch to fix a problem with the assembler's
  new GNU Built note generation feature:  If a note is generated for a
  linkonce section which is then discarded, the relocs referring to that
  discarded section will still be retained, and so cause a link time
  failure.  The fix for now is to skip generating notes for linkonce
  sections, which is not ideal, but works.

Cheers
  Nick

gas/ChangeLog
2018-05-14  Nick Clifton  <nickc@redhat.com>

	* write.c (maybe_generate_build_notes): Generate notes on a
	per-code-section basis.  Skip linkonce sections.

ld/ChangeLog
2018-05-14  Nick Clifton  <nickc@redhat.com>

	* testsuite/ld-elf/notes.exp: New file: Run new test.
	* testsuite/ld-elf/note1_1.s: New file: Source file for test.
	* testsuite/ld-elf/note1_2.s: New file: Source file for test.
	* testsuite/ld-elf/note1.r: New file: Expected readelf output.

Patch


gas/ChangeLog
2018-05-14  Nick Clifton  <nickc@redhat.com>

	* write.c (maybe_generate_build_notes): Generate notes on a
	per-code-section basis.  Skip linkonce sections.

ld/ChangeLog
2018-05-14  Nick Clifton  <nickc@redhat.com>

	* testsuite/ld-elf/notes.exp: New file: Run new test.
	* testsuite/ld-elf/note1_1.s: New file: Source file for test.
	* testsuite/ld-elf/note1_2.s: New file: Source file for test.
	* testsuite/ld-elf/note1.r: New file: Expected readelf output.

diff --git a/gas/write.c b/gas/write.c
index b902bf8565..39c894a8e6 100644
--- a/gas/write.c
+++ b/gas/write.c
@@ -1946,6 +1946,7 @@  maybe_generate_build_notes (void)
   segT      sec;
   char *    note;
   offsetT   note_size;
+  offsetT   total_size;
   offsetT   desc_size;
   offsetT   desc2_offset;
   int       desc_reloc;
@@ -1963,7 +1964,8 @@  maybe_generate_build_notes (void)
 			 SEC_READONLY | SEC_HAS_CONTENTS | SEC_DATA);
   bfd_set_section_alignment (stdoutput, sec, 2);
 
-  /* Create a version note.  */
+  /* Work out the size of the notes that we will create,
+     and the relocation we should use.  */
   if (bfd_arch_bits_per_address (stdoutput) <= 32)
     {
       note_size = 28;
@@ -1997,65 +1999,59 @@  maybe_generate_build_notes (void)
 	desc_reloc = BFD_RELOC_64;
     }
   
-  frag_now_fix ();
-  note = frag_more (note_size);
-  memset (note, 0, note_size);
+  /* We have to create a note for *each* code section.
+     Linker garbage collection might discard some.  */
+  total_size = 0;
+  note = NULL;
 
-  if (target_big_endian)
-    {
-      note[3] = 8; /* strlen (name) + 1.  */
-      note[7] = desc_size; /* Two 8-byte offsets.  */
-      note[10] = NT_GNU_BUILD_ATTRIBUTE_OPEN >> 8;
-      note[11] = NT_GNU_BUILD_ATTRIBUTE_OPEN & 0xff;
-    }
-  else
-    {
-      note[0] = 8; /* strlen (name) + 1.  */
-      note[4] = desc_size; /* Two 8-byte offsets.  */
-      note[8] = NT_GNU_BUILD_ATTRIBUTE_OPEN & 0xff;
-      note[9] = NT_GNU_BUILD_ATTRIBUTE_OPEN >> 8;
-    }
-
-  /* The a1 version number indicates that this note was
-     generated by the assembler and not the gcc annobin plugin.  */
-  memcpy (note + 12, "GA$3a1", 8);
-
-  /* Find the first code section symbol.  */
   for (sym = symbol_rootP; sym != NULL; sym = sym->sy_next)
     if (sym->bsym != NULL
 	&& sym->bsym->flags & BSF_SECTION_SYM
 	&& sym->bsym->section != NULL
-	&& sym->bsym->section->flags & SEC_CODE)
+	/* Skip linkonce sections - we cannot these section symbols as they may disappear.  */
+	&& (sym->bsym->section->flags & (SEC_CODE | SEC_LINK_ONCE)) == SEC_CODE
+	/* Not all linkonce sections are flagged...  */
+	&& strncmp (S_GET_NAME (sym), ".gnu.linkonce", sizeof ".gnu.linkonce" - 1) != 0)
       {
-	/* Found one - now create a relocation against this symbol.  */
-	create_note_reloc (sec, sym, 20, desc_reloc, 0, note);
-	break;
-      }
+	/* Create a version note.  */
+	frag_now_fix ();
+	note = frag_more (note_size);
+	memset (note, 0, note_size);
 
-  /* Find the last code section symbol.  */
-  if (sym)
-    {
-      for (sym = symbol_lastP; sym != NULL; sym = sym->sy_previous)
-	if (sym->bsym != NULL
-	    && sym->bsym->flags & BSF_SECTION_SYM
-	    && sym->bsym->section != NULL
-	    && sym->bsym->section->flags & SEC_CODE)
+	if (target_big_endian)
 	  {
-	    /* Create a relocation against the end of this symbol.  */
-	    create_note_reloc (sec, sym, desc2_offset, desc_reloc,
-			       bfd_get_section_size (sym->bsym->section),
-			       note);
-	    break;
+	    note[3] = 8; /* strlen (name) + 1.  */
+	    note[7] = desc_size; /* Two 8-byte offsets.  */
+	    note[10] = NT_GNU_BUILD_ATTRIBUTE_OPEN >> 8;
+	    note[11] = NT_GNU_BUILD_ATTRIBUTE_OPEN & 0xff;
+	  }
+	else
+	  {
+	    note[0] = 8; /* strlen (name) + 1.  */
+	    note[4] = desc_size; /* Two 8-byte offsets.  */
+	    note[8] = NT_GNU_BUILD_ATTRIBUTE_OPEN & 0xff;
+	    note[9] = NT_GNU_BUILD_ATTRIBUTE_OPEN >> 8;
 	  }
-    }
-  /* else - if we were unable to find any code section symbols then
-     probably there is no code in the output.  So leaving the start
-     and end values as zero in the note is OK.  */
 
-  /* FIXME: Maybe add a note recording the assembler command line and version ?  */
+	/* The a1 version number indicates that this note was
+	   generated by the assembler and not the gcc annobin plugin.  */
+	memcpy (note + 12, "GA$3a1", 8);
+
+	/* Create a relocation to install the start address of the note...  */
+	create_note_reloc (sec, sym, 20, desc_reloc, 0, note);
+
+	/* ...and another one to install the end address.  */
+	create_note_reloc (sec, sym, desc2_offset, desc_reloc,
+			   bfd_get_section_size (sym->bsym->section),
+			   note);
+
+	total_size += note_size;
+	/* FIXME: Maybe add a note recording the assembler command line and version ?  */
+      }
 
   /* Install the note(s) into the section.  */
-  bfd_set_section_contents (stdoutput, sec, (bfd_byte *) note, 0, note_size);
+  if (total_size)
+    bfd_set_section_contents (stdoutput, sec, (bfd_byte *) note, 0, total_size);
   subsegs_finish_section (sec);
   relax_segment (seg_info (sec)->frchainP->frch_root, sec, 0);
   size_seg (stdoutput, sec, NULL);
--- /dev/null	2018-05-14 08:14:06.541999901 +0100
+++ ld/testsuite/ld-elf/notes.exp	2018-05-14 14:29:47.072493865 +0100
@@ -0,0 +1,43 @@ 
+# Expect script for various ELF based Note tests.
+#   Copyright (C) 2018 Free Software Foundation, Inc.
+#
+# This file is part of the GNU Binutils.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
+# MA 02110-1301, USA.
+#
+
+# Exclude non-ELF targets.
+
+if ![is_elf_format] {
+    return
+}
+
+set old_ldflags $LDFLAGS
+if { [istarget spu*-*-*] } {
+    set LDFLAGS "$LDFLAGS --local-store 0:0"
+}
+
+if { [is_remote host] } then {
+    remote_download host merge.ld
+}
+
+run_ld_link_tests [list \
+    [list "Linkonce sections with assembler generated notes" \
+	"-r" "" "--generate-missing-build-notes=yes" \
+	 {note1_1.s note1_2.s} \
+	 {{readelf {--wide --notes} note1.r}} \
+	 "note1.so" ] \
+]
--- /dev/null	2018-05-14 08:14:06.541999901 +0100
+++ ld/testsuite/ld-elf/note1_1.s	2018-05-14 14:47:13.446720472 +0100
@@ -0,0 +1,17 @@ 
+	.section .gnu.linkonce.t.thunk.ax,"ax",%progbits
+	.globl  thunk.ax
+	.hidden thunk.ax
+	.p2align 4
+	.type thunk.ax,%function
+thunk.ax:
+	.dc.l 0
+	.size thunk.ax, . - thunk.ax
+
+	.p2align 4
+	.globl foo
+	.type  foo,%function
+foo:
+	.dc.a thunk.ax
+	.dc.l 0
+	.size foo, . - foo
+
--- /dev/null	2018-05-14 08:14:06.541999901 +0100
+++ ld/testsuite/ld-elf/note1_2.s	2018-05-14 14:47:29.016546423 +0100
@@ -0,0 +1,17 @@ 
+
+	.section .gnu.linkonce.t.thunk.ax,"ax",%progbits
+	.globl  thunk.ax
+	.hidden thunk.ax
+	.p2align 4
+	.type   thunk.ax,%function
+thunk.ax:
+	.dc.l	0
+	.size thunk.ax, . - thunk.ax
+
+	.p2align 4
+	.globl bar
+	.type  bar,%function
+bar:
+	.dc.a	thunk.ax
+	.dc.l	0
+	.size bar, . - bar
--- /dev/null	2018-05-14 08:14:06.541999901 +0100
+++ ld/testsuite/ld-elf/note1.r	2018-05-14 15:22:44.344627946 +0100
@@ -0,0 +1,6 @@ 
+#...
+Displaying notes found in: .gnu.build.attributes
+[ 	]+Owner[ 	]+Data size[ 	]+Description
+[ 	]+GA\$<version>3a1[ 	]+0x000000(08|10)[ 	]+OPEN[ 	]+Applies to region from 0.*
+[ 	]+GA\$<version>3a1[ 	]+0x000000(08|10)[ 	]+OPEN[ 	]+Applies to region from 0.*
+#pass