elf: Strip unreferenced weak undefined symbols
Checks
Context |
Check |
Description |
linaro-tcwg-bot/tcwg_binutils_build--master-aarch64 |
success
|
Testing passed
|
linaro-tcwg-bot/tcwg_binutils_check--master-aarch64 |
success
|
Testing passed
|
linaro-tcwg-bot/tcwg_binutils_build--master-arm |
success
|
Testing passed
|
linaro-tcwg-bot/tcwg_binutils_check--master-arm |
success
|
Testing passed
|
Commit Message
Linker will resolve an undefined symbol only if it is referenced by
relocation. Unreferenced weak undefined symbols serve no purpose.
Weak undefined symbols appear in the dynamic symbol table only when they
are referenced by dynamic relocation. Mark symbols with relocation and
strip undefined weak symbols if they don't have relocation and aren't
in the dynamic symbol table.
bfd/
PR ld/31652
* elf-bfd.h (elf_link_hash_entry): Add has_reloc.
* elf-vxworks.c (elf_vxworks_emit_relocs): Set has_reloc.
* elflink.c (_bfd_elf_link_output_relocs): Likewise.
(elf_link_output_extsym): Strip undefined weak symbols if they
don't have relocation and aren't in the dynamic symbol table.
ld/
PR ld/31652
* testsuite/ld-elf/elf.exp: Run undefweak tests.
* testsuite/ld-elf/undefweak-1.rd: New file.
* testsuite/ld-elf/undefweak-1a.s: Likewise.
* testsuite/ld-elf/undefweak-1b.s: Likewise.
* testsuite/ld-x86-64/weakundef-1.nd: Likewise.
* testsuite/ld-x86-64/weakundef-1a.s: Likewise.
* testsuite/ld-x86-64/weakundef-1b.s: Likewise.
* testsuite/ld-x86-64/x86-64.exp: Run undefweak tests.
---
bfd/elf-bfd.h | 2 +
bfd/elf-vxworks.c | 56 ++++++++++++++-------------
bfd/elflink.c | 17 +++++++-
ld/testsuite/ld-elf/elf.exp | 15 +++++++
ld/testsuite/ld-elf/undefweak-1.rd | 10 +++++
ld/testsuite/ld-elf/undefweak-1a.s | 14 +++++++
ld/testsuite/ld-elf/undefweak-1b.s | 10 +++++
ld/testsuite/ld-x86-64/weakundef-1.nd | 6 +++
ld/testsuite/ld-x86-64/weakundef-1a.s | 6 +++
ld/testsuite/ld-x86-64/weakundef-1b.s | 8 ++++
ld/testsuite/ld-x86-64/x86-64.exp | 18 +++++++++
11 files changed, 134 insertions(+), 28 deletions(-)
create mode 100644 ld/testsuite/ld-elf/undefweak-1.rd
create mode 100644 ld/testsuite/ld-elf/undefweak-1a.s
create mode 100644 ld/testsuite/ld-elf/undefweak-1b.s
create mode 100644 ld/testsuite/ld-x86-64/weakundef-1.nd
create mode 100644 ld/testsuite/ld-x86-64/weakundef-1a.s
create mode 100644 ld/testsuite/ld-x86-64/weakundef-1b.s
Comments
On Thu, Apr 18, 2024 at 05:28:56AM -0700, H.J. Lu wrote:
> Linker will resolve an undefined symbol only if it is referenced by
> relocation. Unreferenced weak undefined symbols serve no purpose.
> Weak undefined symbols appear in the dynamic symbol table only when they
> are referenced by dynamic relocation. Mark symbols with relocation and
> strip undefined weak symbols if they don't have relocation and aren't
> in the dynamic symbol table.
OK, seems reasonable.
I guess I should have asked if you'd tested this patch.
alpha-linux-gnu +FAIL: Generate undefweak-1.a
alpha-linux-gnu +FAIL: Generate undefweak-1.o
alpha-netbsd +FAIL: Generate undefweak-1.a
alpha-netbsd +FAIL: Generate undefweak-1.o
alpha-unknown-freebsd4.7 +FAIL: Generate undefweak-1.a
alpha-unknown-freebsd4.7 +FAIL: Generate undefweak-1.o
d30v-elf +XPASS: Generate undefweak-1.a
d30v-elf +XPASS: Generate undefweak-1.o
dlx-elf +XPASS: Generate undefweak-1.a
dlx-elf +XPASS: Generate undefweak-1.o
fr30-elf +XPASS: Generate undefweak-1.a
fr30-elf +XPASS: Generate undefweak-1.o
frv-elf +XPASS: Generate undefweak-1.a
frv-elf +XPASS: Generate undefweak-1.o
ft32-elf +XPASS: Generate undefweak-1.a
ft32-elf +XPASS: Generate undefweak-1.o
iq2000-elf +XPASS: Generate undefweak-1.a
iq2000-elf +XPASS: Generate undefweak-1.o
mn10200-elf +XPASS: Generate undefweak-1.a
mn10200-elf +XPASS: Generate undefweak-1.o
msp430-elf +XPASS: Generate undefweak-1.a
msp430-elf +XPASS: Generate undefweak-1.o
mt-elf +XPASS: Generate undefweak-1.a
mt-elf +XPASS: Generate undefweak-1.o
pj-elf +XPASS: Generate undefweak-1.a
pj-elf +XPASS: Generate undefweak-1.o
powerpc64-freebsd +FAIL: ld-powerpc/relbrlt
powerpc64le-linux-gnu +FAIL: Build pr26391-3
powerpc64le-linux-gnu +FAIL: Build pr26391-4
powerpc64le-linux-gnu +FAIL: Run pr26391-3
powerpc64le-linux-gnu +FAIL: Run pr26391-4
powerpc64le-linux-gnu +FAIL: ld-powerpc/relbrlt
powerpc64-linux-gnu +FAIL: Build pr26391-3
powerpc64-linux-gnu +FAIL: Build pr26391-4
powerpc64-linux-gnu +FAIL: Run pr26391-3
powerpc64-linux-gnu +FAIL: Run pr26391-4
powerpc64-linux-gnu +FAIL: ld-powerpc/relbrlt
powerpc-eabisim +FAIL: ld-powerpc/relbrlt
powerpc-eabivle +FAIL: ld-powerpc/relbrlt
powerpcle-elf +FAIL: ld-powerpc/relbrlt
powerpc-linux-gnu +FAIL: ld-powerpc/relbrlt
s12z-elf +XPASS: Generate undefweak-1.a
s12z-elf +XPASS: Generate undefweak-1.o
xgate-elf +XPASS: Generate undefweak-1.a
xgate-elf +XPASS: Generate undefweak-1.o
I'm applying the following to fix the powerpc failures, I'll leave the
rest to you.
PR ld/31652
* elflink.c (_bfd_elf_link_output_relocs): Don't segfault
on NULL rel_hash.
diff --git a/bfd/elflink.c b/bfd/elflink.c
index 4f72d1b2a90..6db6a9c0b47 100644
--- a/bfd/elflink.c
+++ b/bfd/elflink.c
@@ -2985,12 +2985,13 @@ _bfd_elf_link_output_relocs (bfd *output_bfd,
* bed->s->int_rels_per_ext_rel);
while (irela < irelaend)
{
- if (*rel_hash)
+ if (rel_hash && *rel_hash)
(*rel_hash)->has_reloc = 1;
(*swap_out) (output_bfd, irela, erel);
irela += bed->s->int_rels_per_ext_rel;
erel += input_rel_hdr->sh_entsize;
- rel_hash++;
+ if (rel_hash)
+ rel_hash++;
}
/* Bump the counter, so that we know where to add the next set of
Thanks again for the patch.
Olivier pointed out that a comment you moved had a duplicate word, and
suggested removing it. Ok to install?
From: Olivier Hainque <hainque@adacore.com>
Date: Mon, 22 Apr 2024 05:30:38 +0000
Remove duplicate word.
for bfd/ChangeLog
PR ld/31652
* elflink.c (_bfd_elf_link_output_relocs): Drop duplicate word.
---
bfd/elf-vxworks.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/bfd/elf-vxworks.c b/bfd/elf-vxworks.c
index 36e5540f9c04..5d91913f097f 100644
--- a/bfd/elf-vxworks.c
+++ b/bfd/elf-vxworks.c
@@ -186,7 +186,7 @@ elf_vxworks_emit_relocs (bfd *output_bfd,
library. We are creating a definition in the output
file but it does not come from any of our normal (.o)
files. ie. a PLT stub. Normally this would be a
- relocation against against SHN_UNDEF with the VMA of
+ relocation against SHN_UNDEF with the VMA of
the PLT stub. This upsets the VxWorks loader.
Convert it to a section-relative relocation. This
gets some other symbols (for instance .dynbss), but
On Sun, Apr 21, 2024 at 10:50 PM Alexandre Oliva <oliva@gnu.org> wrote:
>
> Thanks again for the patch.
>
> Olivier pointed out that a comment you moved had a duplicate word, and
> suggested removing it. Ok to install?
>
> From: Olivier Hainque <hainque@adacore.com>
> Date: Mon, 22 Apr 2024 05:30:38 +0000
>
> Remove duplicate word.
>
> for bfd/ChangeLog
>
> PR ld/31652
> * elflink.c (_bfd_elf_link_output_relocs): Drop duplicate word.
> ---
> bfd/elf-vxworks.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/bfd/elf-vxworks.c b/bfd/elf-vxworks.c
> index 36e5540f9c04..5d91913f097f 100644
> --- a/bfd/elf-vxworks.c
> +++ b/bfd/elf-vxworks.c
> @@ -186,7 +186,7 @@ elf_vxworks_emit_relocs (bfd *output_bfd,
> library. We are creating a definition in the output
> file but it does not come from any of our normal (.o)
> files. ie. a PLT stub. Normally this would be a
> - relocation against against SHN_UNDEF with the VMA of
> + relocation against SHN_UNDEF with the VMA of
> the PLT stub. This upsets the VxWorks loader.
> Convert it to a section-relative relocation. This
> gets some other symbols (for instance .dynbss), but
> --
> 2.25.1
>
I am checking in this as an obvious fix.
@@ -232,6 +232,8 @@ struct elf_link_hash_entry
a strong defined symbol alias. U.ALIAS points to a list of aliases,
the definition having is_weakalias clear. */
unsigned int is_weakalias : 1;
+ /* Symbol has a relocation. */
+ unsigned int has_reloc : 1;
/* String table index in .dynstr if this is a dynamic symbol. */
unsigned long dynstr_index;
@@ -172,35 +172,39 @@ elf_vxworks_emit_relocs (bfd *output_bfd,
irela += bed->s->int_rels_per_ext_rel,
hash_ptr++)
{
- if (*hash_ptr
- && (*hash_ptr)->def_dynamic
- && !(*hash_ptr)->def_regular
- && ((*hash_ptr)->root.type == bfd_link_hash_defined
- || (*hash_ptr)->root.type == bfd_link_hash_defweak)
- && (*hash_ptr)->root.u.def.section->output_section != NULL)
+ if (*hash_ptr)
{
- /* This is a relocation from an executable or shared
- library against a symbol in a different shared
- library. We are creating a definition in the output
- file but it does not come from any of our normal (.o)
- files. ie. a PLT stub. Normally this would be a
- relocation against against SHN_UNDEF with the VMA of
- the PLT stub. This upsets the VxWorks loader.
- Convert it to a section-relative relocation. This
- gets some other symbols (for instance .dynbss), but
- is conservatively correct. */
- for (j = 0; j < bed->s->int_rels_per_ext_rel; j++)
+ (*hash_ptr)->has_reloc = 1;
+ if ((*hash_ptr)->def_dynamic
+ && !(*hash_ptr)->def_regular
+ && ((*hash_ptr)->root.type == bfd_link_hash_defined
+ || (*hash_ptr)->root.type == bfd_link_hash_defweak)
+ && (*hash_ptr)->root.u.def.section->output_section != NULL)
{
- asection *sec = (*hash_ptr)->root.u.def.section;
- int this_idx = sec->output_section->target_index;
-
- irela[j].r_info
- = ELF32_R_INFO (this_idx, ELF32_R_TYPE (irela[j].r_info));
- irela[j].r_addend += (*hash_ptr)->root.u.def.value;
- irela[j].r_addend += sec->output_offset;
+ /* This is a relocation from an executable or shared
+ library against a symbol in a different shared
+ library. We are creating a definition in the output
+ file but it does not come from any of our normal (.o)
+ files. ie. a PLT stub. Normally this would be a
+ relocation against against SHN_UNDEF with the VMA of
+ the PLT stub. This upsets the VxWorks loader.
+ Convert it to a section-relative relocation. This
+ gets some other symbols (for instance .dynbss), but
+ is conservatively correct. */
+ for (j = 0; j < bed->s->int_rels_per_ext_rel; j++)
+ {
+ asection *sec = (*hash_ptr)->root.u.def.section;
+ int this_idx = sec->output_section->target_index;
+
+ irela[j].r_info
+ = ELF32_R_INFO (this_idx,
+ ELF32_R_TYPE (irela[j].r_info));
+ irela[j].r_addend += (*hash_ptr)->root.u.def.value;
+ irela[j].r_addend += sec->output_offset;
+ }
+ /* Stop the generic routine adjusting this entry. */
+ *hash_ptr = NULL;
}
- /* Stop the generic routine adjusting this entry. */
- *hash_ptr = NULL;
}
}
}
@@ -2942,8 +2942,7 @@ _bfd_elf_link_output_relocs (bfd *output_bfd,
asection *input_section,
Elf_Internal_Shdr *input_rel_hdr,
Elf_Internal_Rela *internal_relocs,
- struct elf_link_hash_entry **rel_hash
- ATTRIBUTE_UNUSED)
+ struct elf_link_hash_entry **rel_hash)
{
Elf_Internal_Rela *irela;
Elf_Internal_Rela *irelaend;
@@ -2986,9 +2985,12 @@ _bfd_elf_link_output_relocs (bfd *output_bfd,
* bed->s->int_rels_per_ext_rel);
while (irela < irelaend)
{
+ if (*rel_hash)
+ (*rel_hash)->has_reloc = 1;
(*swap_out) (output_bfd, irela, erel);
irela += bed->s->int_rels_per_ext_rel;
erel += input_rel_hdr->sh_entsize;
+ rel_hash++;
}
/* Bump the counter, so that we know where to add the next set of
@@ -10769,6 +10771,13 @@ elf_link_output_extsym (struct bfd_hash_entry *bh, void *data)
&& (h->root.u.undef.abfd->flags & BFD_PLUGIN) != 0)
strip = true;
+ /* Remember if this symbol should be stripped. */
+ bool should_strip = strip;
+
+ /* Strip undefined weak symbols link if they don't have relocation. */
+ if (!strip)
+ strip = !h->has_reloc && h->root.type == bfd_link_hash_undefweak;
+
type = h->type;
/* If we're stripping it, and it's not a dynamic symbol, there's
@@ -10917,6 +10926,10 @@ elf_link_output_extsym (struct bfd_hash_entry *bh, void *data)
eoinfo->failed = true;
return false;
}
+ /* If a symbol is in the dynamic symbol table and isn't a
+ should-strip symbol, also keep it in the symbol table. */
+ if (!should_strip)
+ strip = false;
}
/* If we are marking the symbol as undefined, and there are no
@@ -171,6 +171,21 @@ run_ld_link_tests [list \
"implib" ] \
] \[uses_genelf\]
+run_ld_link_tests [list \
+ [list "Generate undefweak-1.a" \
+ "" "" \
+ $hpux \
+ {undefweak-1a.s} \
+ {} \
+ "undefweak-1.a" ] \
+ [list "Generate undefweak-1.o" \
+ "-r" "tmpdir/undefweak-1.a" \
+ $hpux \
+ {undefweak-1b.s} \
+ {{readelf {-rsW} undefweak-1.rd}} \
+ "undefweak-1.o" ] \
+] \[uses_genelf\]
+
#v850 gas complains about .tbss.var section attributes.
if { [check_gc_sections_available] && ![istarget "v850-*-*"] } {
run_ld_link_tests {
new file mode 100644
@@ -0,0 +1,10 @@
+#source: undefweak-1a.s
+#source: undefweak-1b.s
+#as:
+#ld: -r
+#readelf: -sW
+
+#failif
+#...
+.*: 0+ +0 +FUNC +WEAK +DEFAULT +UND +bar
+#pass
new file mode 100644
@@ -0,0 +1,14 @@
+ .section .text.foobar,"axG",%progbits,foo,comdat
+ .weak foo
+ .type foo,%function
+foo:
+ .nop
+ .size foo, . - foo
+ .weak bar
+ .set bar, foo
+ .text
+ .global baz
+ .type baz,%function
+baz:
+ .dc.a foo
+ .size baz, . - baz
new file mode 100644
@@ -0,0 +1,10 @@
+ .section .text.foobar,"axG",%progbits,foo,comdat
+ .weak foo
+ .type foo,%function
+foo:
+ .nop
+ .size foo, . - foo
+ .text
+ .global _start
+ .set _start,foo
+ .dc.a baz
new file mode 100644
@@ -0,0 +1,6 @@
+#nm: -n
+#target: x86_64-*-*
+
+#...
+ +w +bar
+#pass
new file mode 100644
@@ -0,0 +1,6 @@
+ .text
+ .global foo
+ .type foo,%function
+foo:
+ .nop
+ .size foo, . - foo
new file mode 100644
@@ -0,0 +1,8 @@
+ .weak bar
+ .text
+ .global _start
+ .type _start,%function
+_start:
+ mov bar@GOTPCREL(%rip), %rax
+ mov foo@GOTPCREL(%rip), %rax
+ .size _start, . - _start
@@ -264,6 +264,24 @@ run_ld_link_tests [list \
{objdump -drj.plt tlsdesc.pd}} \
"libtlsdesc.so" \
] \
+ [list \
+ "Generate x86-64-weakundef-1.so" \
+ "-shared -melf_x86_64" \
+ "" \
+ "--64" \
+ {weakundef-1a.s} \
+ {} \
+ "x86-64-weakundef-1.so" \
+ ] \
+ [list \
+ "Generate x86-64-weakundef-1" \
+ "-melf_x86_64" \
+ "tmpdir/x86-64-weakundef-1.so" \
+ "--64" \
+ {weakundef-1b.s} \
+ {{nm -n weakundef-1.nd}} \
+ "x86-64-weakundef-1" \
+ ] \
]
set test_name "Mixed x86_64 and i386 input test 1"