https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101738
Bug ID: 101738 Summary: Variable value is not set when address passed as register in inline assembly at O2 Product: gcc Version: 12.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: inline-asm Assignee: unassigned at gcc dot gnu.org Reporter: moinakb001 at gmail dot com Target Milestone: --- If one compiles the following code at -O2 (on x86, -v dump follows): ``` void test() { int x = 0x12345678; asm volatile(".asm_label:"::"r"(&x)); } ``` one can see that the stack space allocated for x is not initialized before the inline assembly label (indeed, the store is elided entirely), generating incorrect sequence: ``` test: lea rax, [rsp-4] .asm_label: ret ``` This, in certain cases, would seriously screw up things like inline asm syscall implementations (if one takes address of a stack var). bash # gcc -v Using built-in specs. COLLECT_GCC=gcc COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-pc-linux-gnu/10.3.0/lto-wrapper Target: x86_64-pc-linux-gnu Configured with: /var/tmp/portage/sys-devel/gcc-10.3.0/work/gcc-10.3.0/configure --host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --prefix=/usr --bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/10.3.0 --includedir=/usr/lib/gcc/x86_64-pc-linux-gnu/10.3.0/include --datadir=/usr/share/gcc-data/x86_64-pc-linux-gnu/10.3.0 --mandir=/usr/share/gcc-data/x86_64-pc-linux-gnu/10.3.0/man --infodir=/usr/share/gcc-data/x86_64-pc-linux-gnu/10.3.0/info --with-gxx-include-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/10.3.0/include/g++-v10 --with-python-dir=/share/gcc-data/x86_64-pc-linux-gnu/10.3.0/python --enable-languages=c,c++,fortran --enable-obsolete --enable-secureplt --disable-werror --with-system-zlib --enable-nls --without-included-gettext --enable-checking=release --with-bugurl=https://bugs.gentoo.org/ --with-pkgversion='Gentoo 10.3.0 p1' --disable-esp --enable-libstdcxx-time --enable-shared --enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu --enable-multilib --with-multilib-list=m32,m64 --disable-fixed-point --enable-targets=all --enable-libgomp --disable-libssp --disable-libada --disable-systemtap --disable-vtable-verify --disable-libvtv --without-zstd --enable-lto --without-isl --enable-default-pie --enable-default-ssp Thread model: posix Supported LTO compression algorithms: zlib gcc version 10.3.0 (Gentoo 10.3.0 p1)