Re: [PATCH 1/2] elf: Honour skip_ifunc for cross-object IFUNC relocations [BZ #34428]

On Mon, Aug 3, 2026 at 8:11=E2=80=AFAM H.J. Lu <[email protected]> wrote:
>
> On Mon, Aug 3, 2026 at 7:45=E2=80=AFAM Adhemerval Zanella
> <[email protected]> wrote:
> >
> > Commit 63b31c05a8a dropped the skip_ifunc argument from elf_dynamic_do_=
Rel,
> > assuming the elf_dynamic_do_Rel_irelative pass handles every relocation
> > that may run an IFUNC resolver.  That only holds for IFUNC symbols defi=
ned
> > in the object being relocated, a reference to an IFUNC in another objec=
t is
> > an ordinary JMP_SLOT or GLOB_DAT against an undefined symbol, and being
> > IFUNC is only known after symbol resolution (elf_machine_rel).  Those
> > relocations stay in the regular pass, which no longer propagated
> > skip_ifunc, so __RTLD_NOIFUNC was ignored for them.
> >
> > ldd -u forces non-lazy binding (GLRO(dl_lazy) =3D 0 for DL_DEBUG_UNUSED=
), so
> > the resolver was called and the diagnostic emitted:
> >
> >   $ ldd -u /bin/ls
> >   /bin/ls: Relink `' with `/usr/lib64/libc.so.6' for IFUNC symbol `__me=
mpcpy_chk'
> >
> > ldd -r with LD_BIND_NOW is affected in the same way.
> >
> > Restore the skip_ifunc parameter and pass it through _ELF_DYNAMIC_DO_RE=
LOC
> > and ELF_DYNAMIC_RELOCATE_NOIFUNC.
> >
> > Checked on x86_64-linux-gnu, aarch64-linux-gnu, and i686-linux-gnu. I
> > also built for all supported architectures and run the elf tests on
> > qemu-system for armhf, alpha, hppa, loongarch64, mipsel, mips64le,
> > powerpc*, riscv64, s390x, and sparc64.
> > ---
> >  elf/Makefile                      | 28 +++++++++++++++++++++++
> >  elf/dl-reloc-static-pie.c         |  2 +-
> >  elf/dl-reloc.c                    |  3 ++-
> >  elf/do-rel.h                      | 24 ++++++++++++-------
> >  elf/dynamic-link.h                | 32 ++++++++++++++++----------
> >  elf/tst-ifunc-fault-dep-bindnow.c | 19 ++++++++++++++++
> >  elf/tst-ifunc-fault-dep-lazy.c    | 27 ++++++++++++++++++++++
> >  elf/tst-ifunc-fault-mod.c         | 38 +++++++++++++++++++++++++++++++
> >  8 files changed, 151 insertions(+), 22 deletions(-)
> >  create mode 100644 elf/tst-ifunc-fault-dep-bindnow.c
> >  create mode 100644 elf/tst-ifunc-fault-dep-lazy.c
> >  create mode 100644 elf/tst-ifunc-fault-mod.c
> >
> > diff --git a/elf/Makefile b/elf/Makefile
> > index 94c5b7e6ed8..6cfb1b5cf30 100644
> > --- a/elf/Makefile
> > +++ b/elf/Makefile
> > @@ -1396,6 +1396,13 @@ modules-names +=3D \
> >    tst-ifunc-tls-write-lib \
> >    tst-tls-tdata-reloc-lib \
> >    # modules-names
> > +ifeq (yes,$(have-gcc-ifunc))
> > +tests +=3D \
> > +  tst-ifunc-fault-dep-bindnow \
> > +  tst-ifunc-fault-dep-lazy \
> > +  # tests
> > +modules-names +=3D tst-ifunc-fault-mod
> > +endif
> >  ifneq (no,$(have-test-mtls-descriptor))
> >  tests +=3D tst-ifunc-tls-init-tlsdesc
> >  modules-names +=3D tst-ifunc-tls-init-tlsdesc-lib
> > @@ -2545,6 +2552,27 @@ $(objpfx)tst-ifunc-fault-bindnow.out: $(objpfx)t=
st-ifunc-fault-bindnow \
> >     $(objpfx)ld.so
> >         $(tst-ifunc-fault-script)
> >
> > +LDFLAGS-tst-ifunc-fault-dep-lazy =3D -Wl,-z,lazy
> > +LDFLAGS-tst-ifunc-fault-dep-bindnow =3D -Wl,-z,now
> > +define tst-ifunc-fault-dep-script
> > +( $(test-wrapper) $(rtld-prefix) --verify $< \
> > +  && $(test-wrapper-env) LD_TRACE_LOADED_OBJECTS=3D1 $(rtld-prefix) $<=
 \
> > +  && $(test-wrapper-env) LD_TRACE_LOADED_OBJECTS=3D1 LD_DEBUG=3Dunused=
 \
> > +                        $(rtld-prefix) $< \
> > +  && $(test-wrapper-env) LD_TRACE_LOADED_OBJECTS=3D1 LD_WARN=3Dyes LD_=
BIND_NOW=3D1 \
> > +                        $(rtld-prefix) $< \
> > +) > $@; $(evaluate-test)
> > +endef
> > +$(objpfx)tst-ifunc-fault-dep-lazy: $(objpfx)tst-ifunc-fault-mod.so
> > +$(objpfx)tst-ifunc-fault-dep-bindnow: $(objpfx)tst-ifunc-fault-mod.so
> > +$(objpfx)tst-ifunc-fault-dep-lazy.out: $(objpfx)tst-ifunc-fault-dep-la=
zy \
> > +   $(objpfx)tst-ifunc-fault-mod.so $(objpfx)ld.so
> > +       $(tst-ifunc-fault-dep-script)
> > +$(objpfx)tst-ifunc-fault-dep-bindnow.out: \
> > +   $(objpfx)tst-ifunc-fault-dep-bindnow \
> > +   $(objpfx)tst-ifunc-fault-mod.so $(objpfx)ld.so
> > +       $(tst-ifunc-fault-dep-script)
> > +
> >  LDFLAGS-tst-ifunc-plt-lib.so =3D -Wl,-z,lazy
> >
> >  tst-ifunc-plt-bindnow-ENV =3D LD_BIND_NOW=3D1
> > diff --git a/elf/dl-reloc-static-pie.c b/elf/dl-reloc-static-pie.c
> > index 8463e46147d..53260b57372 100644
> > --- a/elf/dl-reloc-static-pie.c
> > +++ b/elf/dl-reloc-static-pie.c
> > @@ -80,7 +80,7 @@ _dl_relocate_static_pie (void)
> >
> >    /* Relocate ourselves so we can do normal function calls and data ac=
cess
> >       using the global offset table.  IRELATIVE entries are deferred.  =
*/
> > -  ELF_DYNAMIC_RELOCATE_NOIFUNC (main_map, NULL, 0, 0);
> > +  ELF_DYNAMIC_RELOCATE_NOIFUNC (main_map, NULL, 0, 0, 0);
> >
> >    /* Initialize _r_debug_extended.  */
> >    struct r_debug *r =3D _dl_debug_initialize (0, LM_ID_BASE);
> > diff --git a/elf/dl-reloc.c b/elf/dl-reloc.c
> > index 15a6a4cffef..80cd7e25d16 100644
> > --- a/elf/dl-reloc.c
> > +++ b/elf/dl-reloc.c
> > @@ -278,7 +278,8 @@ _dl_relocate_object_no_relro (struct link_map *l, s=
truct r_scope_elem *scope[],
> >         IFUNC resolvers.  Without this, a resolver would see the unrelo=
cated
> >         initialiser bytes that were placed into the slot by the early
> >         _dl_allocate_tls_init.  */
> > -    ELF_DYNAMIC_RELOCATE_NOIFUNC (l, scope, lazy, consider_profiling);
> > +    ELF_DYNAMIC_RELOCATE_NOIFUNC (l, scope, lazy, consider_profiling,
> > +                                 skip_ifunc);
>
> ELF_DYNAMIC_RELOCATE_NOIFUNC name is confusing.
> If it is NOIFUNC, why isn't IFUNC skipped?
>

There are

/* Like ELF_DYNAMIC_RELOCATE but only processes the non-IRELATIVE pass.
   The IRELATIVE pass must be completed later via ELF_DYNAMIC_RELOCATE_IFUN=
C.
   Used by the static-pie startup so the TCB and stack-protector canary can
   be initialised between the two passes.  */
# define ELF_DYNAMIC_RELOCATE_NOIFUNC(map, scope, lazy, consider_profile)

This change makes the comments incorrect.

--=20
H.J.