Re: [PATCH] x86_64: Suppress false positive valgrind error

[Sunil Pandey <skpgkp2@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 5805 bytes --]

On Sun, Feb 25, 2024 at 4:03 PM H.J. Lu <hjl.tools@gmail.com> wrote:

> When strcmp-avx2.S is used as the default, elf/tst-valgrind-smoke fails
> with
>
> ==1272761== Conditional jump or move depends on uninitialised value(s)
> ==1272761==    at 0x4022C98: strcmp (strcmp-avx2.S:462)
> ==1272761==    by 0x400B05B: _dl_name_match_p (dl-misc.c:75)
> ==1272761==    by 0x40085F3: _dl_map_object (dl-load.c:1966)
> ==1272761==    by 0x401AEA4: map_doit (rtld.c:644)
> ==1272761==    by 0x4001488: _dl_catch_exception (dl-catch.c:237)
> ==1272761==    by 0x40015AE: _dl_catch_error (dl-catch.c:256)
> ==1272761==    by 0x401B38F: do_preload (rtld.c:816)
> ==1272761==    by 0x401C116: handle_preload_list (rtld.c:892)
> ==1272761==    by 0x401EDF5: dl_main (rtld.c:1842)
> ==1272761==    by 0x401A79E: _dl_sysdep_start (dl-sysdep.c:140)
> ==1272761==    by 0x401BEEE: _dl_start_final (rtld.c:494)
> ==1272761==    by 0x401BEEE: _dl_start (rtld.c:581)
> ==1272761==    by 0x401AD87: ??? (in */elf/ld.so)
>
> The assembly codes are:
>
>    0x0000000004022c80 <+144>:   vmovdqu 0x20(%rdi),%ymm0
>    0x0000000004022c85 <+149>:   vpcmpeqb 0x20(%rsi),%ymm0,%ymm1
>    0x0000000004022c8a <+154>:   vpcmpeqb %ymm0,%ymm15,%ymm2
>    0x0000000004022c8e <+158>:   vpandn %ymm1,%ymm2,%ymm1
>    0x0000000004022c92 <+162>:   vpmovmskb %ymm1,%ecx
>    0x0000000004022c96 <+166>:   inc    %ecx
> => 0x0000000004022c98 <+168>:   jne    0x4022c32 <strcmp+66>
>
> strcmp-avx2.S has 32-byte vector loads of strings which are shorter than
> 32 bytes:
>
> (gdb) p (char *) ($rdi + 0x20)
> $6 = 0x1ffeffea20 "memcheck-amd64-linux.so"
> (gdb) p (char *) ($rsi + 0x20)
> $7 = 0x4832640 "core-amd64-linux.so"
> (gdb) call (int) strlen ((char *) ($rsi + 0x20))
> $8 = 19
> (gdb) call (int) strlen ((char *) ($rdi + 0x20))
> $9 = 23
> (gdb)
>
> It triggers the valgrind error.  The above code is safe since the loads
> don't cross the page boundary.  Update tst-valgrind-smoke.sh to accept
> an optional suppression file and pass a suppression file to valgrind when
> strcmp-avx2.S is the default implementation of strcmp.
> ---
>  elf/Makefile                           |  3 ++-
>  elf/tst-valgrind-smoke.sh              |  5 +++--
>  sysdeps/x86_64/Makefile                |  6 ++++++
>  sysdeps/x86_64/tst-valgrind-smoke.supp | 17 +++++++++++++++++
>  4 files changed, 28 insertions(+), 3 deletions(-)
>  create mode 100644 sysdeps/x86_64/tst-valgrind-smoke.supp
>
> diff --git a/elf/Makefile b/elf/Makefile
> index 36c04baf02..9d7190f708 100644
> --- a/elf/Makefile
> +++ b/elf/Makefile
> @@ -616,7 +616,8 @@ tests-special += $(objpfx)tst-valgrind-smoke.out
>  endif
>  $(objpfx)tst-valgrind-smoke.out: tst-valgrind-smoke.sh $(objpfx)ld.so
> $(objpfx)valgrind-test
>         $(SHELL) $< $(objpfx)ld.so  $(rtlddir)/$(rtld-installed-name)
> '$(test-wrapper-env)' \
> -               '$(run-program-env)' '$(rpath-link)'
> $(objpfx)valgrind-test > $@; $(evaluate-test)
> +               '$(run-program-env)' '$(rpath-link)'
> $(objpfx)valgrind-test \
> +               '$(valgrind-suppressions-tst-valgrind-smoke)' > $@;
> $(evaluate-test)
>
>  tests += $(tests-execstack-$(have-z-execstack))
>  ifeq ($(run-built-tests),yes)
> diff --git a/elf/tst-valgrind-smoke.sh b/elf/tst-valgrind-smoke.sh
> index e33b2fa1d7..7d0ceac6b1 100644
> --- a/elf/tst-valgrind-smoke.sh
> +++ b/elf/tst-valgrind-smoke.sh
> @@ -25,6 +25,7 @@ test_wrapper_env="$3"
>  run_program_env="$4"
>  library_path="$5"
>  test_prog="$6"
> +valgrind_suppressions="$7"
>
>  # Test whether valgrind is available in the test
>  # environment.  If not, skip the test.
> @@ -34,7 +35,7 @@ ${test_wrapper_env} ${run_program_env} \
>  # Test valgrind works with the system ld.so in the test environment
>  /bin/sh -c \
>    "${test_wrapper_env} ${run_program_env} \
> -   valgrind -q --error-exitcode=1 \
> +   valgrind -q --error-exitcode=1 ${valgrind_suppressions} \
>       ${system_rtld} /bin/echo ${system_rtld}" || exit 77
>
>  # Finally the actual test inside the test environment,
> @@ -42,5 +43,5 @@ ${test_wrapper_env} ${run_program_env} \
>  # the smoke test under valgrind.
>  /bin/sh -c \
>    "${test_wrapper_env} ${run_program_env} \
> -   valgrind -q --error-exitcode=1 \
> +   valgrind -q --error-exitcode=1 ${valgrind_suppressions} \
>       ${rtld} --library-path ${library_path} ${test_prog} ${rtld}"
> diff --git a/sysdeps/x86_64/Makefile b/sysdeps/x86_64/Makefile
> index 145f25e7f6..07b4a532ae 100644
> --- a/sysdeps/x86_64/Makefile
> +++ b/sysdeps/x86_64/Makefile
> @@ -211,6 +211,12 @@ tst-plt-rewrite2-ENV =
> GLIBC_TUNABLES=glibc.cpu.plt_rewrite=2
>  $(objpfx)tst-plt-rewrite2: $(objpfx)tst-plt-rewritemod2.so
>  endif
>
> +# Check if ISA level is 3 or above.
> +ifneq (,$(filter $(have-x86-isa-level),$(x86-isa-level-3-or-above)))
> +valgrind-suppressions-tst-valgrind-smoke = \
> +  --suppressions=$(..)sysdeps/x86_64/tst-valgrind-smoke.supp
> +endif
> +
>  endif # $(subdir) == elf
>
>  ifeq ($(subdir),csu)
> diff --git a/sysdeps/x86_64/tst-valgrind-smoke.supp
> b/sysdeps/x86_64/tst-valgrind-smoke.supp
> new file mode 100644
> index 0000000000..533c2deaff
> --- /dev/null
> +++ b/sysdeps/x86_64/tst-valgrind-smoke.supp
> @@ -0,0 +1,17 @@
> +{
> +   False positive at strcmp-avx2.S:462
> +   Memcheck:Cond
> +   fun:strcmp
> +   fun:_dl_name_match_p
> +   fun:_dl_map_object
> +   fun:map_doit
> +   fun:_dl_catch_exception
> +   fun:_dl_catch_error
> +   fun:do_preload
> +   fun:handle_preload_list
> +   fun:dl_main
> +   fun:_dl_sysdep_start
> +   fun:_dl_start_final
> +   fun:_dl_start
> +   obj:*/elf/ld.so
> +}
> --
> 2.43.2
>

LGTM
Reviewed-by: Sunil K Pandey <skpgkp2@gmail.com>