[PATCH] as: Replace the removed symbol with the versioned symbol

[H.J. Lu]

On Wed, Aug 11, 2021 at 6:11 PM Fangrui Song <i@maskray.me> wrote:
>
>
> On 2021-08-11, H.J. Lu wrote:
> >On Tue, Aug 10, 2021 at 2:56 PM Fangrui Song <i@maskray.me> wrote:
> >>
> >> On 2021-08-01, H.J. Lu via Binutils wrote:
> >> >When a symbol removed by .symver is used in relocation and there is one
> >> >and only one versioned symbol, don't remove the symbol.  Instead, mark
> >> >it to be removed and replace the removed symbol used in relocation with
> >> >the versioned symbol before generating relocation.
> >>
> >> Thanks for the patch.
> >> The behavior looks good.
> >>
> >> .symver foo, foo@v1, remove
> >> .globl foo
> >> foo:
> >>    call foo   # R_X86_64_PLT32 foo@v1
> >>
> >>
> >>
> >> I think this can be extended to non-remove one-@ as well.
> >> The unadorned symbol and relocations referencing it just add complexity
> >> to linker internals.
> >>
> >> .symver foo, foo@v1
> >
> >This usage is perfectly fine and quite normal.
>
> It isn't.
>
> cat > a.s <<eof
> .symver foo, foo@v1
> .globl foo
> foo:
> eof

We must keep foo since there may be relocations
against foo in this file as well as in other files.

> cat > a.ver <<eof
> v1 {};
> v2 { foo*; };
> eof
> cc -c a.s
>
> % ld.bfd --version-script=a.ver -shared a.o -o a.so && nm -D a.so
> 0000000000001000 R foo@v1
> 0000000000000000 A v1
> 0000000000000000 A v2

This looks normal.

>
> If
> .symver foo_v1, foo@v1
>
> % ld.bfd --version-script=a.ver -shared a.o -o a.so && nm -D a.so
> 0000000000001000 R foo@v1
> 0000000000001000 R foo_v1@@v2
> 0000000000000000 A v1
> 0000000000000000 A v2

This looks normal.

>
> Merging (unadorned) foo and (non-default versioned) foo@v1 is a hack, in all of GNU ld, gold, and ld.lld.



-- 
H.J.