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x86_64: Suppress false positive valgrind error

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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.
Reviewed-by: Sunil K Pandey <skpgkp2@gmail.com>
This commit is contained in:
H.J. Lu 2024-02-25 16:03:26 -08:00
parent 8c7c188d62
commit a1735e0aa8
4 changed files with 28 additions and 3 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

3
elf/Makefile
View file

@ -617,7 +617,8 @@ tests-special += $(objpfx)tst-valgrind-smoke.out
endif endif
$(objpfx)tst-valgrind-smoke.out: tst-valgrind-smoke.sh $(objpfx)ld.so $(objpfx)valgrind-test $(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)' \ $(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)) tests += $(tests-execstack-$(have-z-execstack))
ifeq ($(run-built-tests),yes) ifeq ($(run-built-tests),yes)

5
elf/tst-valgrind-smoke.sh
View file

@ -25,6 +25,7 @@ test_wrapper_env="$3"
run_program_env="$4" run_program_env="$4"
library_path="$5" library_path="$5"
test_prog="$6" test_prog="$6"
valgrind_suppressions="$7"
# Test whether valgrind is available in the test # Test whether valgrind is available in the test
# environment. If not, skip the test. # environment. If not, skip the test.
@ -34,7 +35,7 @@ ${test_wrapper_env} ${run_program_env} \
# Test valgrind works with the system ld.so in the test environment # Test valgrind works with the system ld.so in the test environment
/bin/sh -c \ /bin/sh -c \
"${test_wrapper_env} ${run_program_env} \ "${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 ${system_rtld} /bin/echo ${system_rtld}" || exit 77
# Finally the actual test inside the test environment, # Finally the actual test inside the test environment,
@ -42,5 +43,5 @@ ${test_wrapper_env} ${run_program_env} \
# the smoke test under valgrind. # the smoke test under valgrind.
/bin/sh -c \ /bin/sh -c \
"${test_wrapper_env} ${run_program_env} \ "${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}" ${rtld} --library-path ${library_path} ${test_prog} ${rtld}"

6
sysdeps/x86_64/Makefile
View file

@ -211,6 +211,12 @@ tst-plt-rewrite2-ENV = GLIBC_TUNABLES=glibc.cpu.plt_rewrite=2
$(objpfx)tst-plt-rewrite2: $(objpfx)tst-plt-rewritemod2.so $(objpfx)tst-plt-rewrite2: $(objpfx)tst-plt-rewritemod2.so
endif endif
# Check if ISA level is 3 or above.
ifneq (,$(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 endif # $(subdir) == elf
ifeq ($(subdir),csu) ifeq ($(subdir),csu)

17
sysdeps/x86_64/tst-valgrind-smoke.supp Normal file
View file

@ -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
}