Bug 6931 - COMDAT group is broken
Summary: COMDAT group is broken
Status: RESOLVED FIXED
Alias: None
Product: binutils
Classification: Unclassified
Component: ld (show other bugs)
Version: 2.20
: P2 normal
Target Milestone: ---
Assignee: Alan Modra
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2008-10-01 19:17 UTC by H.J. Lu
Modified: 2008-10-04 07:03 UTC (History)
2 users (show)

See Also:
Host:
Target:
Build:
Last reconfirmed: 2008-10-02 14:42:55

Attachments
Testcases (353 bytes, patch)
2008-10-02 01:09 UTC, H.J. Lu 		Details | Diff
View All Add an attachment (proposed patch, testcase, etc.)

Note You need to log in before you can comment on or make changes to this bug.
Description H.J. Lu 2008-10-01 19:17:38 UTC 
This patch:

http://sourceware.org/ml/binutils/2008-09/msg00214.html

may have caused:

[hjl@gnu-31 tmp]$ cat foo.c
extern int foo;
int *
foo1 ()
{
  return &foo;
}
[hjl@gnu-31 tmp]$ cat bar.c
extern int bar;
int *
bar1 ()
{
  return &bar;
}
[hjl@gnu-31 tmp]$ gcc -fPIC -c bar.c foo.c
[hjl@gnu-31 tmp]$ ld -r -o libbar.o bar.o
[hjl@gnu-31 tmp]$ ld -shared libbar.o foo.o
foo.o: In function `__i686.get_pc_thunk.cx':
foo.c:(.text.__i686.get_pc_thunk.cx[__i686.get_pc_thunk.cx]+0x0): multiple
definition of `__i686.get_pc_thunk.cx'
libbar.o:(.text.__i686.get_pc_thunk.cx[.group]+0x0): first defined here
[hjl@gnu-31 tmp]$
Comment 1 H.J. Lu 2008-10-01 19:18:22 UTC 
It happens on Linux/ia32 with gcc 4.3.
Comment 2 H.J. Lu 2008-10-01 23:15:36 UTC 
The bug is in bfd_elf_set_group_contents:

  symindx = 0; 
  if (elf_group_id (sec) != NULL)
    symindx = elf_group_id (sec)->udata.i;

  if (symindx == 0)
    {
      /* If called from the assembler, swap_out_syms will have set up
         elf_section_syms;  If called for "ld -r", use target_index.  */
      if (elf_section_syms (abfd) != NULL)
        symindx = elf_section_syms (abfd)[sec->index]->udata.i;
      else
        symindx = sec->target_index;
    }
  elf_section_data (sec)->this_hdr.sh_info = symindx;

"ld -r" is incorrect. We need to find the symbol index for
group signature which isn't the same as the section name.
Comment 3 H.J. Lu 2008-10-02 01:09:37 UTC 
Created attachment 2974 [details]
Testcases

Those tests failed:

FAIL: ld-elf/group4
FAIL: ld-elf/group5
FAIL: ld-elf/group6
Comment 4 Alan Modra 2008-10-02 14:42:55 UTC 
Testing a fix.  I know now why I hacked the group signature into the SEC_GROUP
name...
Comment 6 H.J. Lu 2008-10-03 15:16:06 UTC 
It still isn't right:

bash-3.2$ cat
/export/gnu/src/binutils/binutils/binutils/testsuite/binutils-all/group.s
	.section .text.foo,"axG",%progbits,foo_group,comdat
	.global foo
foo:
	.word 0
	.section .data.foo,"awG",%progbits,foo_group,comdat
	.global bar
bar:
	.word 0
bash-3.2$ cat
/export/gnu/src/binutils/binutils/binutils/testsuite/binutils-all/group-2.s
	.section .text.foo,"axG",%progbits,.text.foo,comdat
	.global foo2
foo2:
	.word 0
	.section .data.bar,"awG",%progbits,.text.foo,comdat
	.global bar2
bar2:
	.word 0
bash-3.2$ gcc -c
/export/gnu/src/binutils/binutils/binutils/testsuite/binutils-all/group.s
/export/gnu/src/binutils/binutils/binutils/testsuite/binutils-all/group-2.s
bash-3.2$ ./ld-new -r group.o group-2.o
bash-3.2$ readelf -g group-2.o

COMDAT group section [    1] `.group' [.text.foo] contains 2 sections:
   [Index]    Name
   [    5]   .text.foo
   [    6]   .data.bar
bash-3.2$ readelf -g a.out 

COMDAT group section [    1] `foo_group' [foo_group] contains 2 sections:
   [Index]    Name
   [    4]   .text.foo
   [    7]   .data.foo

COMDAT group section [    2] `.group' [.text.foo.1] contains 2 sections:
   [Index]    Name
   [    5]   .text.foo.1
   [    8]   .data.bar
bash-3.2$ 

"ld -r" generates wrong group signature.