https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110834
Bug ID: 110834 Summary: Incorrect format-nonliteral warning when wrapping a printf-family function using __builtin_va_arg_pack Product: gcc Version: 13.2.1 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: ksperling at apple dot com Target Milestone: --- Created attachment 55650 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55650&action=edit pre-processed example code When wrapping a printf-family function (e.g. printf, sprintf, …) with an inline wrapper that uses __builtin_va_arg_pack() to forward the format arguments a format-nonliteral warning is incorrectly generated, even thought the format string argument is annotated with the correct format attribute, e.g. this code #include <stdio.h> __inline__ __attribute__((__always_inline__, __format__(printf, 1, 2))) int myprintf(char const *fmt, ...) { return printf(fmt, __builtin_va_arg_pack()); } results in the following warning (or error with -Werror) $ gcc -c -Wformat -Werror=format-nonliteral format_va_arg_pack.c format_va_arg_pack.c: In function ‘myprintf’: format_va_arg_pack.c:6:5: error: format not a string literal, argument types not checked [-Werror=format-nonliteral] 6 | return printf(fmt, __builtin_va_arg_pack()); | ^~~~~~ cc1: some warnings being treated as errors The gcc output below and the attached .i file were generated with gcc 10.2.1 on Debian, but I have verified that the issue also reproduces on gcc 13.2 and gcc trunk on godbolt.org (https://godbolt.org/z/q6xMs5481). For a real-world manifestation of this issue, see https://github.com/openwrt/openwrt/issues/13016 where this issue is triggered by wrapper functions of this style that are part of the fortify-headers library (https://git.2f30.org/fortify-headers/). Full compiler output with -v: Using built-in specs. COLLECT_GCC=gcc OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa:hsa OFFLOAD_TARGET_DEFAULT=1 Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Debian 10.2.1-6' --with-bugurl=file:///usr/share/doc/gcc-10/README.Bugs --enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++,m2 --prefix=/usr --with-gcc-major-version-only --program-suffix=-10 --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 --enable-bootstrap --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-plugin --enable-default-pie --with-system-zlib --enable-libphobos-checking=release --with-target-system-zlib=auto --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=/build/gcc-10-Km9U7s/gcc-10-10.2.1/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-10-Km9U7s/gcc-10-10.2.1/debian/tmp-gcn/usr,hsa --without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu --with-build-config=bootstrap-lto-lean --enable-link-mutex Thread model: posix Supported LTO compression algorithms: zlib zstd gcc version 10.2.1 20210110 (Debian 10.2.1-6) COLLECT_GCC_OPTIONS='-v' '-save-temps' '-c' '-Wformat=1' '-Werror=format-nonliteral' '-mtune=generic' '-march=x86-64' /usr/lib/gcc/x86_64-linux-gnu/10/cc1 -E -quiet -v -imultiarch x86_64-linux-gnu format_va_arg_pack.c -mtune=generic -march=x86-64 -Wformat=1 -Werror=format-nonliteral -fpch-preprocess -fasynchronous-unwind-tables -o format_va_arg_pack.i ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu" ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/10/include-fixed" ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/10/../../../../x86_64-linux-gnu/include" #include "..." search starts here: #include <...> search starts here: /usr/lib/gcc/x86_64-linux-gnu/10/include /usr/local/include /usr/include/x86_64-linux-gnu /usr/include End of search list. COLLECT_GCC_OPTIONS='-v' '-save-temps' '-c' '-Wformat=1' '-Werror=format-nonliteral' '-mtune=generic' '-march=x86-64' /usr/lib/gcc/x86_64-linux-gnu/10/cc1 -fpreprocessed format_va_arg_pack.i -quiet -dumpbase format_va_arg_pack.c -mtune=generic -march=x86-64 -auxbase format_va_arg_pack -Wformat=1 -Werror=format-nonliteral -version -fasynchronous-unwind-tables -o format_va_arg_pack.s GNU C17 (Debian 10.2.1-6) version 10.2.1 20210110 (x86_64-linux-gnu) compiled by GNU C version 10.2.1 20210110, GMP version 6.2.1, MPFR version 4.1.0, MPC version 1.2.0, isl version isl-0.23-GMP GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 GNU C17 (Debian 10.2.1-6) version 10.2.1 20210110 (x86_64-linux-gnu) compiled by GNU C version 10.2.1 20210110, GMP version 6.2.1, MPFR version 4.1.0, MPC version 1.2.0, isl version isl-0.23-GMP GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 Compiler executable checksum: 1f803793fa2e3418c492b25e7d3eac2f format_va_arg_pack.c: In function ‘myprintf’: format_va_arg_pack.c:6:5: error: format not a string literal, argument types not checked [-Werror=format-nonliteral] 6 | return printf(fmt, __builtin_va_arg_pack()); | ^~~~~~ cc1: some warnings being treated as errors