https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120408
Bug ID: 120408
Summary: Missed memset (len + 1) tree build_string() in
gcc/tree.cc at
98575a51f588428a8c5c9d7c28d473c4a22caa7e
Product: gcc
Version: 16.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: kaelfandrew at gmail dot com
Target Milestone: ---
Created attachment 61495
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=61495&action=edit
C code
Compiling the C code attachment shows f0_slow() is not optimize like f0() with
flags -O3 -fallow-store-data-races from godbolt -v:
============================
Using built-in specs.
COLLECT_GCC=/opt/compiler-explorer/gcc-snapshot/bin/gcc
Target: x86_64-linux-gnu
Configured with: ../gcc-trunk-20250522/configure
--prefix=/opt/compiler-explorer/gcc-build/staging
--enable-libstdcxx-backtrace=yes --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu --disable-bootstrap
--enable-multiarch --with-abi=m64 --with-multilib-list=m32,m64,mx32
--enable-multilib --enable-clocale=gnu
--enable-languages=c,c++,fortran,ada,objc,obj-c++,go,d,rust,m2,cobol
--enable-ld=yes --enable-gold=yes --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --enable-linker-build-id --enable-lto
--enable-plugins --enable-threads=posix
--with-pkgversion=Compiler-Explorer-Build-gcc-035ab47366eb7560a9c69b2ebc7307c309e9e909-binutils-2.42
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 16.0.0 20250522 (experimental)
(Compiler-Explorer-Build-gcc-035ab47366eb7560a9c69b2ebc7307c309e9e909-binutils-2.42)
COLLECT_GCC_OPTIONS='-fdiagnostics-color=always' '-g' '-o' '/app/output.s'
'-masm=intel' '-fno-verbose-asm' '-S' '-v' '-mtune=generic' '-march=x86-64'
'-dumpdir' '/app/'
/opt/compiler-explorer/gcc-trunk-20250522/bin/../libexec/gcc/x86_64-linux-gnu/16.0.0/cc1
-quiet -v -imultiarch x86_64-linux-gnu -iprefix
/opt/compiler-explorer/gcc-trunk-20250522/bin/../lib/gcc/x86_64-linux-gnu/16.0.0/
<source> -quiet -dumpdir /app/ -dumpbase output.c -dumpbase-ext .c -masm=intel
-mtune=generic -march=x86-64 -g -version -fdiagnostics-color=always
-fno-verbose-asm -o /app/output.s
GNU C23
(Compiler-Explorer-Build-gcc-035ab47366eb7560a9c69b2ebc7307c309e9e909-binutils-2.42)
version 16.0.0 20250522 (experimental) (x86_64-linux-gnu)
compiled by GNU C version 11.4.0, GMP version 6.2.1, MPFR version
4.1.0, MPC version 1.2.1, isl version isl-0.24-GMP
GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
ignoring nonexistent directory
"/opt/compiler-explorer/gcc-trunk-20250522/bin/../lib/gcc/x86_64-linux-gnu/16.0.0/../../../../x86_64-linux-gnu/include"
ignoring duplicate directory
"/opt/compiler-explorer/gcc-trunk-20250522/bin/../lib/gcc/../../lib/gcc/x86_64-linux-gnu/16.0.0/include"
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring duplicate directory
"/opt/compiler-explorer/gcc-trunk-20250522/bin/../lib/gcc/../../lib/gcc/x86_64-linux-gnu/16.0.0/include-fixed/x86_64-linux-gnu"
ignoring duplicate directory
"/opt/compiler-explorer/gcc-trunk-20250522/bin/../lib/gcc/../../lib/gcc/x86_64-linux-gnu/16.0.0/include-fixed"
ignoring nonexistent directory
"/opt/compiler-explorer/gcc-trunk-20250522/bin/../lib/gcc/../../lib/gcc/x86_64-linux-gnu/16.0.0/../../../../x86_64-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/opt/compiler-explorer/gcc-trunk-20250522/bin/../lib/gcc/x86_64-linux-gnu/16.0.0/include
/opt/compiler-explorer/gcc-trunk-20250522/bin/../lib/gcc/x86_64-linux-gnu/16.0.0/include-fixed/x86_64-linux-gnu
/opt/compiler-explorer/gcc-trunk-20250522/bin/../lib/gcc/x86_64-linux-gnu/16.0.0/include-fixed
/usr/local/include
/opt/compiler-explorer/gcc-trunk-20250522/bin/../lib/gcc/../../include
/usr/include/x86_64-linux-gnu
/usr/include
End of search list.
Compiler executable checksum: 6344123aa07ae9474e9bb3b0aee8dab3
COMPILER_PATH=/opt/compiler-explorer/gcc-trunk-20250522/bin/../libexec/gcc/x86_64-linux-gnu/16.0.0/:/opt/compiler-explorer/gcc-trunk-20250522/bin/../libexec/gcc/x86_64-linux-gnu/:/opt/compiler-explorer/gcc-trunk-20250522/bin/../libexec/gcc/:/opt/compiler-explorer/gcc-trunk-20250522/bin/../lib/gcc/x86_64-linux-gnu/16.0.0/../../../../x86_64-linux-gnu/bin/
LIBRARY_PATH=/opt/compiler-explorer/gcc-trunk-20250522/bin/../lib/gcc/x86_64-linux-gnu/16.0.0/:/opt/compiler-explorer/gcc-trunk-20250522/bin/../lib/gcc/x86_64-linux-gnu/:/opt/compiler-explorer/gcc-trunk-20250522/bin/../lib/gcc/:/opt/compiler-explorer/gcc-trunk-20250522/bin/../lib/gcc/x86_64-linux-gnu/16.0.0/../../../../lib64/:/lib/x86_64-linux-gnu/:/lib/../lib64/:/usr/lib/x86_64-linux-gnu/:/usr/lib/../lib64/:/opt/compiler-explorer/gcc-trunk-20250522/bin/../lib/gcc/x86_64-linux-gnu/16.0.0/../../../../x86_64-linux-gnu/lib/:/opt/compiler-explorer/gcc-trunk-20250522/bin/../lib/gcc/x86_64-linux-gnu/16.0.0/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-fdiagnostics-color=always' '-g' '-o' '/app/output.s'
'-masm=intel' '-fno-verbose-asm' '-S' '-v' '-mtune=generic' '-march=x86-64'
'-dumpdir' '/app/output.'
Compiler returned: 0
====================
Line 2569 of build_string() at tree.cc shows:
```
if (str)
memcpy (s->string.str, str, len);
else
memset (s->string.str, 0, len);
s->string.str[len] = '\0';
```
This patch should hopefully helps:
```
diff --git a/gcc/tree.cc b/gcc/tree.cc
index 98575a51f58..d3a07a665b4 100644
--- a/gcc/tree.cc
+++ b/gcc/tree.cc
@@ -2567,10 +2567,12 @@ build_string (unsigned len, const char *str /*= NULL
*/)
TREE_CONSTANT (s) = 1;
TREE_STRING_LENGTH (s) = len;
if (str)
- memcpy (s->string.str, str, len);
+ {
+ memcpy (s->string.str, str, len);
+ s->string.str[len] = '\0';
+ }
else
- memset (s->string.str, 0, len);
- s->string.str[len] = '\0';
+ memset (s->string.str, 0, len + 1);
return s;
}
```
