Gcc 4.5 miscompiles the following code: char buf[1024]; void add_input_file(int file) { (*((int **)&buf))[0] = file; }
it results in this asm: Disassembly of section .text: 00000000 <add_input_file>: 0: c3 ret The file argument is completly ignored. gcc4.4 does the right thing: Disassembly of section .text: 00000000 <add_input_file>: 0: a1 00 00 00 00 mov 0x0,%eax 5: 8b 54 24 04 mov 0x4(%esp),%edx 9: 89 10 mov %edx,(%eax) b: c3 ret The command used to produce this output was i486-openwrt-linux-gcc -c asdf.c -fomit-frame-pointer -Os -o asdf2.o Openwrt adds a number of patches to gcc, they can be seen here: https://dev.openwrt.org/browser/trunk/toolchain/gcc/patches/4.5.0 None of them should interfer with the codegeneration for x86. The problem doesn't seem to happen with the mips target. This is the output of gcc -v: Using built-in specs. COLLECT_GCC=../staging_dir/toolchain-i386_gcc-4.5.0_uClibc-0.9.30.3/usr/bin/i486-openwrt-linux-gcc COLLECT_LTO_WRAPPER=/home/asdf/openwrt/trunk/staging_dir/toolchain-i386_gcc-4.5.0_uClibc-0.9.30.3/usr/libexec/gcc/i486-openwrt-linux-uclibc/4.5.0/lto-wrapper Target: i486-openwrt-linux-uclibc Configured with: /home/asdf/openwrt/trunk/build_dir/toolchain-i386_gcc-4.5.0_uClibc-0.9.30.3/gcc-4.5.0/configure --prefix=/home/asdf/openwrt/trunk/staging_dir/toolchain-i386_gcc-4.5.0_uClibc-0.9.30.3/usr --build=i586-redhat-linux --host=i586-redhat-linux --target=i486-openwrt-linux-uclibc --with-gnu-ld --enable-target-optspace --disable-libgomp --disable-libmudflap --disable-multilib --disable-nls --with-ppl --with-cloog --with-host-libstdcxx=-lstdc++ --with-gmp=/home/asdf/openwrt/trunk/staging_dir/host --with-mpfr=/home/asdf/openwrt/trunk/staging_dir/host --disable-decimal-float --disable-libssp --disable-__cxa_atexit --enable-languages=c,c++ --enable-shared --enable-threads --with-slibdir=/home/asdf/openwrt/trunk/staging_dir/toolchain-i386_gcc-4.5.0_uClibc-0.9.30.3/lib --enable-lto --disable-tls Thread model: posix gcc version 4.5.0 (GCC) -- Summary: miscompilation with -Os on x86 Product: gcc Version: 4.5.0 Status: UNCONFIRMED Severity: major Priority: P3 Component: target AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: bernhardloos at googlemail dot com GCC target triplet: i486-openwrt-linux-uclibc http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44060