From a1735e0aa858f0c8b15e5ee9975bff4279423680 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Sun, 25 Feb 2024 16:03:26 -0800
Subject: x86_64: Suppress false positive valgrind error

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>
---
 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 02dc476e27..f0439ef634 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -617,7 +617,8 @@ 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 9337e95093..66b21954f3 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
+}
-- 
cgit 1.4.1