[PATCH v2] elf: Add DL_ADDRESS_WITHOUT_RELOC [BZ #33088]

[H.J. Lu]

On Mon, Jun 16, 2025 at 3:47 PM Florian Weimer <fweimer@redhat.com> wrote:
>
> * H. J. Lu:
>
> > diff --git a/elf/dl-before-reloc.h b/elf/dl-before-reloc.h
> > new file mode 100644
> > index 0000000000..4da1bcb776
> > --- /dev/null
> > +++ b/elf/dl-before-reloc.h
> > @@ -0,0 +1,30 @@
>
> > +static __always_inline const void *
> > +_dl_get_var_before_reloc (const void *var)
> > +{
> > +  const void *address = var;
> > +  /* Force VAR into a general purpose register to prevent loading it
> > +     into a vector register directly.  */
> > +  asm ("" : "+r"(address));
> > +  return address;
> > +}
>
> I think this has to be a macro unfortunately (with a statement
> expression), to preserve type safety.  And for
> HIDDEN_VAR_NEEDS_DYNAMIC_RELOC architectures, the macro should just
> expand to its argument because for those architectures, we deal with the
> problem by other means.
>
> I would prefer DL_ADDRESS_WITHOUT_RELOC or something like that, to show
> that this is a macro (but maybe that's not important), and to not imply
> that it only works before relocation.
>

Done.  Here is  the patch:

Add DL_ADDRESS_WITHOUT_RELOC to force an address into a general purpose
register to prevent loading it into a vector register directly before
run-time relocation.  Change _end from

extern char _end[] attribute_hidden;

to

extern char _end attribute_hidden;

so that DL_ADDRESS_WITHOUT_RELOC can be used to get its address.

This is an updated fix for BZ #33088.

-- 
H.J.
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