https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83172
Bug ID: 83172 Summary: -Wstack-size= doesn't detect the correct stack size with VLA or alloca Product: gcc Version: 4.8.5 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: hao.hou at utah dot edu Target Milestone: --- Created attachment 42723 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42723&action=edit The preprocessed source code repoduce the bug The -Wstack-usage= doesn't deduce the correct stack size and reports an unbounded stack size in the following case: 1. The function uses a variable length array 2. The function uses alloca Even with alloca(constant) or __builtin_unreachable hints the VLA size, compiler still mark the max stack size unbounded. Another related option -Wvla-larger-than= does inferred the maximum VLA size from the __builtin_unreachable hints. The expected behavior should be -Wstack-usage= also follows the hint, at least, for the alloca(constant) case, it should realize the stack size could not be unbounded. GCC Version: Using built-in specs. COLLECT_GCC=gcc-7 COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/7/lto-wrapper OFFLOAD_TARGET_NAMES=nvptx-none OFFLOAD_TARGET_DEFAULT=1 Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu 7.1.0-10ubuntu1~16.04.york0' --with-bugurl=file:///usr/share/doc/gcc-7/README.Bugs --enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr --with-gcc-major-version-only --program-suffix=-7 --program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-libmpx --enable-plugin --with-system-zlib --with-target-system-zlib --enable-objc-gc=auto --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-offload-targets=nvptx-none --without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix gcc version 7.1.0 (Ubuntu 7.1.0-10ubuntu1~16.04.york0) And the preprocessed file that repo this bug is attached. The command used to repo the bug and it's output: $ gcc-7 -save-temps -Wvla-larger-than=128 -Wstack-usage=102400 -O3 -c t.c t.c: In function ‘stack_usage_only’: t.c:21:5: warning: stack usage might be unbounded [-Wstack-usage=] int stack_usage_only(unsigned x) ^~~~~~~~~~~~~~~~ t.c: In function ‘alloca_fails_even_with_const’: t.c:30:5: warning: stack usage might be unbounded [-Wstack-usage=] int alloca_fails_even_with_const() ^~~~~~~~~~~~~~~~~~~~~~~~~~~~ Expected: Compiles without any warning.