Re: [PATCH] riscv: Drop reliance on _GLOBAL_OFFSET_TABLE_[0]

["Fāng-ruì Sòng" <maskray@google.com>]

On Wed, Aug 18, 2021 at 9:22 AM Palmer Dabbelt <palmerdabbelt@google.com> wrote:
>
> On Tue, 17 Aug 2021 21:37:44 PDT (-0700), maskray@google.com wrote:
> > &__ehdr_start is a better way to get the load address.
> >
> > This is similar to commits b37b75d269883a2c553bb7019a813094eb4e2dd1
> > (x86-64) and 43d06ed218fc8be58987bdfd00e21e5720f0b862 (aarch64).
> > ---
> >  sysdeps/riscv/dl-machine.h | 21 ++++++++++-----------
> >  1 file changed, 10 insertions(+), 11 deletions(-)
> >
> > diff --git a/sysdeps/riscv/dl-machine.h b/sysdeps/riscv/dl-machine.h
> > index aedf69fcdd..5b0746175c 100644
> > --- a/sysdeps/riscv/dl-machine.h
> > +++ b/sysdeps/riscv/dl-machine.h
> > @@ -76,27 +76,26 @@ elf_machine_matches_host (const ElfW(Ehdr) *ehdr)
> >    return 1;
> >  }
> >
> > +/* Return the run-time load address of the shared object.  */
> > +static inline ElfW(Addr)
> > +elf_machine_load_address (void)
> > +{
> > +  extern const ElfW(Ehdr) __ehdr_start attribute_hidden;
> > +  return (ElfW(Addr)) &__ehdr_start;
> > +}
> > +
> >  /* Return the link-time address of _DYNAMIC.  */
> >  static inline ElfW(Addr)
> >  elf_machine_dynamic (void)
> >  {
> > -  extern ElfW(Addr) _GLOBAL_OFFSET_TABLE_ __attribute__ ((visibility ("hidden")));
> > -  return _GLOBAL_OFFSET_TABLE_;
> > +  extern ElfW(Dyn) _DYNAMIC[] attribute_hidden;
> > +  return (ElfW(Addr)) _DYNAMIC - elf_machine_load_address ();
> >  }
> >
> >  #define STRINGXP(X) __STRING (X)
> >  #define STRINGXV(X) STRINGV_ (X)
> >  #define STRINGV_(...) # __VA_ARGS__
> >
> > -/* Return the run-time load address of the shared object.  */
> > -static inline ElfW(Addr)
> > -elf_machine_load_address (void)
> > -{
> > -  ElfW(Addr) load_addr;
> > -  asm ("lla %0, _DYNAMIC" : "=r" (load_addr));
> > -  return load_addr - elf_machine_dynamic ();
> > -}
> > -
> >  /* Initial entry point code for the dynamic linker.
> >     The C function `_dl_start' is the real entry point;
> >     its return value is the user program's entry point.  */
>
> Reviewed-by: Palmer Dabbelt <palmerdabbelt@google.com>
> Acked-by: Palmer Dabbelt <palmerdabbelt@google.com>
>
> LMK if you want me to commit this, but from the history it looks like
> you have commit access so feel free to yourself (assuming you've built
> it for all our targets).
>
> Thanks!

I have the commit access:)

Checked with  scripts/build-many-glibcs.py /tmp/glibc-many glibcs
riscv64-linux-gnu-rv64imafdc-lp64d --keep all
(and riscv32-linux-gnu-rv32imac-ilp32) and ran elf/ldconfig &
elf/ld.so with qemu-riscv64-static.