Message ID | 20210924160948.4123839-1-maskray@google.com |
---|---|
State | New |
Headers | show |
Series | [v2] i386: Port elf_machine_{load_address,dynamic} from x86-64 | expand |
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.
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