https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112947
Bug ID: 112947
Summary: Contradictory indications of extern __thread address
NULL or not with UBSAN
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: resence at parsoma dot net
Target Milestone: ---
Created attachment 56848
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=56848&action=edit
The main code which reproduces this issue
I have not managed to reduce this below 2 files.
File 1, m.c:
__thread int nimInErrorMode__system_u4299;
File 2, g.c, attached.
Then run:
gcc -c -Wall -Wextra -pedantic -pthread -fsanitize=undefined -O0
-fno-strict-aliasing -o m.o m.c
gcc -c -Wall -Wextra -pedantic -pthread -fsanitize=undefined -O2
-fno-strict-aliasing -o g.o g.c
gcc -o repro m.o g.o -fsanitize=undefined -lpthread
With the output:
g.c: In function ‘nimErrorFlag’:
g.c:25:40: warning: the comparison will always evaluate as ‘false’ for the
address of ‘nimInErrorMode__system_u4299’ will never be NULL [-Waddress]
25 | if (((&nimInErrorMode__system_u4299) == (void *)0)) {
| ^~
g.c:16:21: note: ‘nimInErrorMode__system_u4299’ declared here
16 | extern __thread int nimInErrorMode__system_u4299;
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
Always-false comparison is true
gcc -v output, running from Debian unstable on amd64:
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-linux-gnu/13/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 13.2.0-8'
--with-bugurl=file:///usr/share/doc/gcc-13/README.Bugs
--enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++,m2 --prefix=/usr
--with-gcc-major-version-only --program-suffix=-13
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/libexec --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --enable-bootstrap --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-plugin --enable-default-pie --with-system-zlib
--enable-libphobos-checking=release --with-target-system-zlib=auto
--enable-objc-gc=auto --enable-multiarch --disable-werror --enable-cet
--with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32
--enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none=/build/reproducible-path/gcc-13-13.2.0/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/reproducible-path/gcc-13-13.2.0/debian/tmp-gcn/usr
--enable-offload-defaulted --without-cuda-driver --enable-checking=release
--build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
--with-build-config=bootstrap-lto-lean --enable-link-serialization=3
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 13.2.0 (Debian 13.2.0-8)
