https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67730
Bug ID: 67730 Summary: [5.2 Regression] No warning when returning NULL in void function Product: gcc Version: 5.2.0 Status: UNCONFIRMED Severity: major Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: damwdan at gmail dot com Target Milestone: --- Created attachment 36401 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36401&action=edit preprocessed source file Following up on this Stackoverflow post: http://stackoverflow.com/q/32732281/5366270 There seems to be a regression in gcc 5.2.0. When returning NULL in a void function, gcc *does not* warn or error. gcc 4.9.2 (and some other previous versions, as mentioned in the post) warns. clang 3.7 errors. As noted by "Marc Glisse", using -Wsystem-headers does the trick and generates a warning. Though, the preprocessed output (attached) is exactly the same. $ cat c.c #include <stddef.h> void procedure(void) { return NULL; } $ gcc -Wall -Wextra -std=c99 -pedantic -c c.c $ gcc -Wall -Wextra -std=c99 -pedantic -Wsystem-headers -c c.c In file included from c.c:1:0: c.c: In function ‘procedure’: c.c:5:12: warning: ‘return’ with a value, in function returning void return NULL; ^ $ gcc -v Using built-in specs. COLLECT_GCC=gcc COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-unknown-linux-gnu/5.2.0/lto-wrapper Target: x86_64-unknown-linux-gnu Configured with: /build/gcc-multilib/src/gcc-5.2.0/configure --prefix=/usr --libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/ --enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++ --enable-shared --enable-threads=posix --enable-libmpx --with-system-zlib --with-isl --enable-__cxa_atexit --disable-libunwind-exceptions --enable-clocale=gnu --disable-libstdcxx-pch --disable-libssp --enable-gnu-unique-object --enable-linker-build-id --enable-lto --enable-plugin --enable-install-libiberty --with-linker-hash-style=gnu --enable-gnu-indirect-function --enable-multilib --disable-werror --enable-checking=release --with-default-libstdcxx-abi=gcc4-compatible Thread model: posix gcc version 5.2.0 (GCC) Note that the bug also appears when returning NULL in an int or char function, but not double (an error is generated).