[v2] i386: Port elf_machine_{load_address,dynamic} from x86-64
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dj/TryBot-apply_patch |
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Patch applied to master at the time it was sent
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dj/TryBot-32bit |
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Build for i686
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Commit Message
This drops reliance on _GLOBAL_OFFSET_TABLE_[0] being the link-time
address of _DYNAMIC.
The code sequence length does not change.
---
Changes from v1:
* Change ElfW(xxx) to Elf32_xxx
---
sysdeps/i386/dl-machine.h | 27 ++++++++++-----------------
1 file changed, 10 insertions(+), 17 deletions(-)
Comments
On Fri, Sep 24, 2021 at 9:10 AM Fangrui Song <maskray@google.com> wrote:
>
> This drops reliance on _GLOBAL_OFFSET_TABLE_[0] being the link-time
> address of _DYNAMIC.
>
> The code sequence length does not change.
> ---
> Changes from v1:
> * Change ElfW(xxx) to Elf32_xxx
> ---
> sysdeps/i386/dl-machine.h | 27 ++++++++++-----------------
> 1 file changed, 10 insertions(+), 17 deletions(-)
>
> diff --git a/sysdeps/i386/dl-machine.h b/sysdeps/i386/dl-machine.h
> index 590b41d8d7..0401888508 100644
> --- a/sysdeps/i386/dl-machine.h
> +++ b/sysdeps/i386/dl-machine.h
> @@ -34,27 +34,20 @@ elf_machine_matches_host (const Elf32_Ehdr *ehdr)
> }
>
>
> -/* Return the link-time address of _DYNAMIC. Conveniently, this is the
> - first element of the GOT, a special entry that is never relocated. */
> -static inline Elf32_Addr __attribute__ ((unused, const))
> -elf_machine_dynamic (void)
> -{
> - /* This produces a GOTOFF reloc that resolves to zero at link time, so in
> - fact just loads from the GOT register directly. By doing it without
> - an asm we can let the compiler choose any register. */
> - extern const Elf32_Addr _GLOBAL_OFFSET_TABLE_[] attribute_hidden;
> - return _GLOBAL_OFFSET_TABLE_[0];
> -}
> -
> /* Return the run-time load address of the shared object. */
> static inline Elf32_Addr __attribute__ ((unused))
> elf_machine_load_address (void)
> {
> - /* Compute the difference between the runtime address of _DYNAMIC as seen
> - by a GOTOFF reference, and the link-time address found in the special
> - unrelocated first GOT entry. */
> - extern Elf32_Dyn bygotoff[] asm ("_DYNAMIC") attribute_hidden;
> - return (Elf32_Addr) &bygotoff - elf_machine_dynamic ();
> + extern const Elf32_Ehdr __ehdr_start attribute_hidden;
> + return (Elf32_Addr) &__ehdr_start;
> +}
> +
> +/* Return the link-time address of _DYNAMIC. */
> +static inline Elf32_Addr __attribute__ ((unused))
> +elf_machine_dynamic (void)
> +{
> + extern Elf32_Dyn _DYNAMIC[] attribute_hidden;
> + return (Elf32_Addr) _DYNAMIC - elf_machine_load_address ();
> }
>
> /* Set up the loaded object described by L so its unrelocated PLT
> --
> 2.33.0.685.g46640cef36-goog
>
LGTM.
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
Thanks.
@@ -34,27 +34,20 @@ elf_machine_matches_host (const Elf32_Ehdr *ehdr)
}
-/* Return the link-time address of _DYNAMIC. Conveniently, this is the
- first element of the GOT, a special entry that is never relocated. */
-static inline Elf32_Addr __attribute__ ((unused, const))
-elf_machine_dynamic (void)
-{
- /* This produces a GOTOFF reloc that resolves to zero at link time, so in
- fact just loads from the GOT register directly. By doing it without
- an asm we can let the compiler choose any register. */
- extern const Elf32_Addr _GLOBAL_OFFSET_TABLE_[] attribute_hidden;
- return _GLOBAL_OFFSET_TABLE_[0];
-}
-
/* Return the run-time load address of the shared object. */
static inline Elf32_Addr __attribute__ ((unused))
elf_machine_load_address (void)
{
- /* Compute the difference between the runtime address of _DYNAMIC as seen
- by a GOTOFF reference, and the link-time address found in the special
- unrelocated first GOT entry. */
- extern Elf32_Dyn bygotoff[] asm ("_DYNAMIC") attribute_hidden;
- return (Elf32_Addr) &bygotoff - elf_machine_dynamic ();
+ extern const Elf32_Ehdr __ehdr_start attribute_hidden;
+ return (Elf32_Addr) &__ehdr_start;
+}
+
+/* Return the link-time address of _DYNAMIC. */
+static inline Elf32_Addr __attribute__ ((unused))
+elf_machine_dynamic (void)
+{
+ extern Elf32_Dyn _DYNAMIC[] attribute_hidden;
+ return (Elf32_Addr) _DYNAMIC - elf_machine_load_address ();
}
/* Set up the loaded object described by L so its unrelocated PLT