Re: [PATCH] Hurd: Enable ifunc by default

[H.J. Lu]

On Mon, Jan 18, 2021 at 4:04 PM Samuel Thibault via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> (leaving gcc out, it's really out of the story, it just happens to
> expose support for ifunc)
>
> Joseph Myers, le lun. 18 janv. 2021 20:05:44 +0000, a ecrit:
> > /scratch/jmyers/glibc-bot/install/compilers/i686-gnu/lib/gcc/i686-glibc-gnu/11.0.0/../../../../i686-glibc-gnu/bin/ld:
> >  
> > /scratch/jmyers/glibc-bot/build/compilers/i686-gnu/glibc/i686-gnu/elf/librtld.os:
> >  in function `hurd_file_name_lookup_retry':
> > (.text+0x1e08e): undefined reference to `strncpy'
>
> The story seems complex and related to the glibc rtld build rules.
>
> - We need hurd/lookup-retry.c in the rtld
> - It happens to use strncpy since ee11682d4f5 ("hurd: Fix strcpy calls")
> - strncpy happens to have a hidden def in libc
> - hurd/lookup-retry.os thus refers to __GI_strncpy rather than strncpy
> - dl-allobjs.os thus includes strncpy-c.os (that provides __GI_strncpy),
> and not strncpy.os (that provides strncpy)
> - librtld.map thus contains strncpy-c.os only, and not strncpy.os
> - thus no rtld-strncpy.os is getting built
> - thus strncpy is not available in rtld
> - but strncpy doesn't have a hidden def in rtld
> - and thus hurd/rtld-lookup-retry.os refers to strncpy, not __GI_strncpy
> - thus the link failure.
>
> The base issue I see here is that dl-allobjs is based on libc-built
> objects that might be using hidden defs while rtld-built objects might
> not.
>
> But we could also say that it's strncpy that should also have a hidden
> def in rtld. The attached patch does this, is this ok?
>

String function usage in ld.so must be carefully managed.  Why doesn't
hurd ld.so build script mark strncpy as needed?


-- 
H.J.