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)
