[Valgrind-developers] [valgrind] add_hardwired_spec for ld-linux-x86-64.so.2 memcmp

[Mark W. <ma...@so...>]

https://sourceware.org/git/gitweb.cgi?p=valgrind.git;h=9ffdeb4927b8505cc5a9ea54f608f4972166bb0e

commit 9ffdeb4927b8505cc5a9ea54f608f4972166bb0e
Author: Mark Wielaard <ma...@kl...>
Date:   Wed Mar 12 13:57:19 2025 +0100

    add_hardwired_spec for ld-linux-x86-64.so.2 memcmp
    
    With RPATH processing ld.so compiled for x86-64-v3 uses an optimized
    avx2 memcmp (bcmp) which causes (false postive) memcheck invalid reads
    of size 32 warnings.
    
    Fix this my adding a hardwire spec with a simpler memcmp for
    ld-linux-x86-64.so.2.
    
    https://bugs.kde.org/show_bug.cgi?id=501348
    
    Authored-by: Florian Weimer <fw...@re...>

Diff:
---
 NEWS                            |  1 +
 coregrind/m_redir.c             |  9 +++++++++
 coregrind/m_trampoline.S        | 19 +++++++++++++++++++
 coregrind/pub_core_trampoline.h |  1 +
 4 files changed, 30 insertions(+)

diff --git a/NEWS b/NEWS
index 16cfeef2a4..7025d61af7 100644
--- a/NEWS
+++ b/NEWS
@@ -58,6 +58,7 @@ are not entered into bugzilla tend to get forgotten about or ignored.
 499212  mmap() with MAP_ALIGNED() returns unaligned pointer
 501119  memcheck/tests/pointer-trace fails when run on NFS filesystem
 501194  Fix ML_(check_macho_and_get_rw_loads) so that it is correct for any number of segment commands
+501348 glibc built with -march=x86-64-v3 does not work due to ld.so memcmp
 
 
 To see details of a given bug, visit
diff --git a/coregrind/m_redir.c b/coregrind/m_redir.c
index 5e7bc42f97..63172b9717 100644
--- a/coregrind/m_redir.c
+++ b/coregrind/m_redir.c
@@ -1431,6 +1431,15 @@ void VG_(redir_initialise) ( void )
          NULL
 #        else
          complain_about_stripped_glibc_ldso
+#        endif
+      );
+      add_hardwired_spec(
+         "ld-linux-x86-64.so.2", "memcmp",
+         (Addr)&VG_(amd64_linux_REDIR_FOR_memcmp),
+#        ifndef GLIBC_MANDATORY_STRLEN_REDIRECT
+         NULL
+#        else
+         complain_about_stripped_glibc_ldso
 #        endif
       );
    }
diff --git a/coregrind/m_trampoline.S b/coregrind/m_trampoline.S
index 4860a2259f..2c2cc0dc2a 100644
--- a/coregrind/m_trampoline.S
+++ b/coregrind/m_trampoline.S
@@ -241,6 +241,25 @@ VG_(amd64_linux_REDIR_FOR_strcmp):
 	ret
 .size VG_(amd64_linux_REDIR_FOR_strcmp), .-VG_(amd64_linux_REDIR_FOR_strcmp)
 
+.global VG_(amd64_linux_REDIR_FOR_memcmp)
+.type   VG_(amd64_linux_REDIR_FOR_memcmp), @function
+VG_(amd64_linux_REDIR_FOR_memcmp):
+	xorl	%ecx, %ecx
+	jmp	2f
+1:
+	movzbl	(%rdi, %rcx), %eax
+	movzbl	(%rsi, %rcx), %r8d
+	addq	$1, %rcx
+	subl	%r8d, %eax
+	jne	3f
+2:
+	cmpq	%rcx, %rdx
+	jne	1b
+	xorl	%eax, %eax
+3:
+	ret
+.size VG_(amd64_linux_REDIR_FOR_memcmp), .-VG_(amd64_linux_REDIR_FOR_memcmp)
+
 .global VG_(amd64_linux_REDIR_FOR_index)
 .type   VG_(amd64_linux_REDIR_FOR_index), @function
 VG_(amd64_linux_REDIR_FOR_index):
diff --git a/coregrind/pub_core_trampoline.h b/coregrind/pub_core_trampoline.h
index db497c51a5..11d791df7c 100644
--- a/coregrind/pub_core_trampoline.h
+++ b/coregrind/pub_core_trampoline.h
@@ -82,6 +82,7 @@ extern Addr VG_(amd64_linux_REDIR_FOR_vtime);
 extern Addr VG_(amd64_linux_REDIR_FOR_vgetcpu);
 extern UInt VG_(amd64_linux_REDIR_FOR_strlen)( void* );
 extern Int VG_(amd64_linux_REDIR_FOR_strcmp)( void*, void* );
+extern Int VG_(amd64_linux_REDIR_FOR_memcmp)( void*, void*, SizeT );
 extern Char* VG_(amd64_linux_REDIR_FOR_index) ( const Char*, Int );
 #endif