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* [glibc] i386: Port elf_machine_{load_address,dynamic} from x86-64
@ 2021-09-24 16:36 Fangrui Song
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From: Fangrui Song @ 2021-09-24 16:36 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=91e92272caefad4b6156572fc41671dcbd93afe5
commit 91e92272caefad4b6156572fc41671dcbd93afe5
Author: Fangrui Song <maskray@google.com>
Date: Fri Sep 24 09:36:32 2021 -0700
i386: Port elf_machine_{load_address,dynamic} from x86-64
This drops reliance on _GLOBAL_OFFSET_TABLE_[0] being the link-time
address of _DYNAMIC.
The code sequence length does not change.
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
Diff:
---
sysdeps/i386/dl-machine.h | 25 +++++++++----------------
1 file changed, 9 insertions(+), 16 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)
+/* Return the run-time load address of the shared object. */
+static inline Elf32_Addr __attribute__ ((unused))
+elf_machine_load_address (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];
+ extern const Elf32_Ehdr __ehdr_start attribute_hidden;
+ return (Elf32_Addr) &__ehdr_start;
}
-/* Return the run-time load address of the shared object. */
+/* Return the link-time address of _DYNAMIC. */
static inline Elf32_Addr __attribute__ ((unused))
-elf_machine_load_address (void)
+elf_machine_dynamic (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 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
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