[PATCH v2] s390: Do not use canonical PLT if pointer equality is not needed

[Alan Modra]

On Mon, Mar 16, 2026 at 06:07:47PM +0100, Jens Remus wrote:
> +# PR 29655 (cont.): Check that in PIC code linked as PDE taking the address
> +# of a function defined in a DSO results in the function address (from GOT)
> +# and not the "canonical PLT" address from the PDE.
> +# This is just an optimization and both is valid, although libraries may
> +# depend on this specific behavior, so do not complain loudly.
> +setup_xfail *-*-*
> +clear_xfail i?86-*-* powerpc*-*-* s390x-*-* x86_64-*-*
> +run_ld_link_exec_tests [list \
> +    [list \
> +	"Run pr29655" \
> +	"$NOPIE_LDFLAGS -Wl,--no-as-needed,-rpath,tmpdir tmpdir/pr29655.so" \
> +	"" \
> +	{ pr29655b.c } \
> +	"pr29655" \
> +	"pass.out" \
> +	"-fPIC" \
> +    ] \
> +]

A test that needs to be run is inferior to a test that compiles and
examines an object, because the former only works natively.  I think
you can likely turn this into a run_cc_link_tests that checks the
executable with readelf --dyn-sym looking for a zero value undefined
fun_public.
eg. this (s390x)
     6: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND fun_public

Not this (s390), which is defining the sym on a plt stub (via ld.so
magic) and would therefore fail when run.
     8: 00400424     0 FUNC    GLOBAL DEFAULT  UND fun_public

For the cross-toolchain targets that I test, it looks like
aarch64-linux, alpha-linux, arm-linux, hppa-linux, ia64-linux,
microblaze-linux, mips-linux, mips64-linux-gnuabi64,
powerpc64le-linux, powerpc64-linux, powerpc-linux, s390x-linux and
x86_64-pc-linux will pass.

m68k-linux, riscv64-linux, s390-linux, sh4-linux, sparc64-linux and
tilepro-linux will fail.

-- 
Alan Modra