PATCH: PR ld/10270: IFUNC local symbol
H.J. Lu
hjl.tools@gmail.com
Sun Jun 14 22:41:00 GMT 2009
On Fri, Jun 12, 2009 at 11:01 PM, Ulrich Drepper<drepper@redhat.com> wrote:
>
>> The other issue can be seen with:
>> gcc -O2 -fpic -shared -o ifunc3lib1.{so,c}
>> gcc -O2 -o ifunc3 ./ifunc3lib1.so
>> ./ifunc3lib1
>> Here, &lib1t3 in the binary resolves to a .plt slot in the binary, while
>> &lib1t3 in the shared library resolves to the actual address the ifunc
>> returned.
>> Not sure what exactly we want to do here, but the function pointers should
>> be the same.
>
> It's tricky alright. There really isn't a good answer for this. The
> existing behavior is the only sensible solution. One could try to make
> things more complicated by changing the linker to associate the symbol
> with the PLT slot and somehow allow ld.so to recognize such symbols, but
> I think it's not worth it.
>
> This all comes about only because IFUNCs are used in situations where
> they really were not meant to be used. IFUNC are supposed to be
> definitions in DSOs which can be used in place of FUNC symbols. This
> will work without changes to any semantics.
>
> In your test case you're creating and IFUNC symbol in the executable.
> While I have no problem with supporting it this does mean the program
> author take responsibility for doing this. I think we can in this case
> very well live with the difference in function addresses.
>
> Therefore I suggest to leave this case and just document it.
>
Hi,
I am checking in this patch to disallow dynamic IFUNC pointer in
non-shared object.
--
H.J.
---
bfd/
2009-06-14 H.J. Lu <hongjiu.lu@intel.com>
PR ld/10270
* elf32-i386.c (elf_i386_allocate_dynrelocs): Disallow
dynamic IFUNC pointer in non-shared object. Use .got.plt
for IFUNC definition in PIE.
(elf_i386_allocate_dynrelocs): Resolve IFUNC definition in
PIE locally.
* elf64-x86-64.c (elf64_x86_64_allocate_dynrelocs): Disallow
dynamic IFUNC pointer in non-shared object. Use .got.plt
for IFUNC definition in PIE.
(elf64_x86_64_relocate_section): Resolve IFUNC definition in
PIE locally.
ld/testsuite/
2009-06-14 H.J. Lu <hongjiu.lu@intel.com>
PR ld/10270
* ld-ifunc/ifunc-9-x86.d: New.
* ld-ifunc/ifunc-9-x86.s: Likewise.
-------------- next part --------------
bfd/
2009-06-14 H.J. Lu <hongjiu.lu@intel.com>
PR ld/10270
* elf32-i386.c (elf_i386_allocate_dynrelocs): Disallow
dynamic IFUNC pointer in non-shared object. Use .got.plt
for IFUNC definition in PIE.
(elf_i386_allocate_dynrelocs): Resolve IFUNC definition in
PIE locally.
* elf64-x86-64.c (elf64_x86_64_allocate_dynrelocs): Disallow
dynamic IFUNC pointer in non-shared object. Use .got.plt
for IFUNC definition in PIE.
(elf64_x86_64_relocate_section): Resolve IFUNC definition in
PIE locally.
ld/testsuite/
2009-06-14 H.J. Lu <hongjiu.lu@intel.com>
PR ld/10270
* ld-ifunc/ifunc-9-x86.d: New.
* ld-ifunc/ifunc-9-x86.s: Likewise.
Index: ld/testsuite/ld-ifunc/ifunc-9-x86.d
===================================================================
--- ld/testsuite/ld-ifunc/ifunc-9-x86.d (revision 0)
+++ ld/testsuite/ld-ifunc/ifunc-9-x86.d (revision 0)
@@ -0,0 +1,3 @@
+#ld: --export-dynamic
+#error: .*dynamic STT_GNU_IFUNC symbool `foo' with pointer equality in `.*.o' can not be used when making an executable; recompile with -fPIE and relink with -pie
+#target: x86_64-*-* i?86-*-*
Index: ld/testsuite/ld-ifunc/ifunc-9-x86.s
===================================================================
--- ld/testsuite/ld-ifunc/ifunc-9-x86.s (revision 0)
+++ ld/testsuite/ld-ifunc/ifunc-9-x86.s (revision 0)
@@ -0,0 +1,18 @@
+ .text
+ .type foo, %gnu_indirect_function
+.globl foo
+ .type foo, @function
+foo:
+ ret
+ .size foo, .-foo
+ .type start,"function"
+ .global start
+start:
+ .type _start,"function"
+ .global _start
+_start:
+ .type __start,"function"
+ .global __start
+__start:
+ .type __start,"function"
+ movl foo, %eax
Index: bfd/elf64-x86-64.c
===================================================================
--- bfd/elf64-x86-64.c (revision 6121)
+++ bfd/elf64-x86-64.c (working copy)
@@ -1982,6 +1982,27 @@ elf64_x86_64_allocate_dynrelocs (struct
{
asection *plt, *gotplt, *relplt;
+ /* When a shared library references a STT_GNU_IFUNC symbol
+ defined in executable. the .got.plt slot in the shared library
+ will contain address of the .plt slot in the binary and only
+ its .got.plt will contain the resolved function that should be
+ called. Pointer equality won't work correctly. PIE should
+ be used if pointer equality is required here. */
+ if (!info->shared
+ && (h->dynindx != -1
+ || info->export_dynamic)
+ && h->pointer_equality_needed)
+ {
+ info->callbacks->einfo
+ (_("%F%P: dynamic STT_GNU_IFUNC symbool `%s' with pointer "
+ "equality in `%B' can not be used when making an "
+ "executable; recompile with -fPIE and relink with -pie\n"),
+ h->root.root.string,
+ h->root.u.def.section->owner);
+ bfd_set_error (bfd_error_bad_value);
+ return FALSE;
+ }
+
/* Return and discard space for dynamic relocations against it if
it is never referenced in a non-shared object. */
if (!h->ref_regular)
@@ -2049,8 +2070,9 @@ elf64_x86_64_allocate_dynrelocs (struct
not dynamic.
2. Use .got.plt in a non-shared object if pointer equality
isn't needed.
- 3. Use .got.plt if .got isn't used.
- 4. Otherwise use .got so that it can be shared among different
+ 3. Use .got.plt in PIE.
+ 4. Use .got.plt if .got isn't used.
+ 5. Otherwise use .got so that it can be shared among different
objects at run-time.
We only need to relocate .got entry in shared object. */
if ((info->shared
@@ -2058,6 +2080,7 @@ elf64_x86_64_allocate_dynrelocs (struct
|| h->forced_local))
|| (!info->shared
&& !h->pointer_equality_needed)
+ || (info->executable && info->shared)
|| htab->sgot == NULL)
{
/* Use .got.plt. */
@@ -2914,7 +2937,8 @@ elf64_x86_64_relocate_section (bfd *outp
+ input_section->output_offset);
if (h->dynindx == -1
- || h->forced_local)
+ || h->forced_local
+ || info->executable)
{
/* This symbol is resolved locally. */
outrel.r_info = ELF64_R_INFO (0, R_X86_64_IRELATIVE);
Index: bfd/elf32-i386.c
===================================================================
--- bfd/elf32-i386.c (revision 6121)
+++ bfd/elf32-i386.c (working copy)
@@ -2143,6 +2143,27 @@ elf_i386_allocate_dynrelocs (struct elf_
{
asection *plt, *gotplt, *relplt;
+ /* When a shared library references a STT_GNU_IFUNC symbol
+ defined in executable. the .got.plt slot in the shared library
+ will contain address of the .plt slot in the binary and only
+ its .got.plt will contain the resolved function that should be
+ called. Pointer equality won't work correctly. PIE should
+ be used if pointer equality is required here. */
+ if (!info->shared
+ && (h->dynindx != -1
+ || info->export_dynamic)
+ && h->pointer_equality_needed)
+ {
+ info->callbacks->einfo
+ (_("%F%P: dynamic STT_GNU_IFUNC symbool `%s' with pointer "
+ "equality in `%B' can not be used when making an "
+ "executable; recompile with -fPIE and relink with -pie\n"),
+ h->root.root.string,
+ h->root.u.def.section->owner);
+ bfd_set_error (bfd_error_bad_value);
+ return FALSE;
+ }
+
/* Return and discard space for dynamic relocations against it if
it is never referenced in a non-shared object. */
if (!h->ref_regular)
@@ -2210,8 +2231,9 @@ elf_i386_allocate_dynrelocs (struct elf_
not dynamic.
2. Use .got.plt in a non-shared object if pointer equality
isn't needed.
- 3. Use .got.plt if .got isn't used.
- 4. Otherwise use .got so that it can be shared among different
+ 3. Use .got.plt in PIE.
+ 4. Use .got.plt if .got isn't used.
+ 5. Otherwise use .got so that it can be shared among different
objects at run-time.
We only need to relocate .got entry in shared object. */
if ((info->shared
@@ -2219,6 +2241,7 @@ elf_i386_allocate_dynrelocs (struct elf_
|| h->forced_local))
|| (!info->shared
&& !h->pointer_equality_needed)
+ || (info->executable && info->shared)
|| htab->sgot == NULL)
{
/* Use .got.plt. */
@@ -3194,7 +3217,8 @@ elf_i386_relocate_section (bfd *output_b
+ offset);
if (h->dynindx == -1
- || h->forced_local)
+ || h->forced_local
+ || info->executable)
{
/* This symbol is resolved locally. */
outrel.r_info = ELF32_R_INFO (0, R_386_IRELATIVE);
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