[Bug c/81980] New: Spurious -Wmissing-format-attribute warning in 32-bit mode

["sgunderson at bigfoot dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81980

            Bug ID: 81980
           Summary: Spurious -Wmissing-format-attribute warning in 32-bit
                    mode
           Product: gcc
           Version: 7.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sgunderson at bigfoot dot com
  Target Milestone: ---

Hi,

The following (reduced) code gives a warning if and only if I add -m32:

atum17:~> cat test.c
#include <stdarg.h>

char a;
void set_message(const char *fmt, va_list ap)
  __attribute__((format(printf, 1, 0)));
void set_message_by_errcode(va_list ap) { set_message(&a, ap); }

atum17:~> gcc -Wmissing-format-attribute -c test.c     
atum17:~> gcc -Wmissing-format-attribute -c test.c -m32
test.cc: In function ‘void set_message_by_errcode(va_list)’:
test.cc:6:61: warning: function ‘void set_message_by_errcode(va_list)’ might be
a candidate for ‘gnu_printf’ format attribute [-Wsuggest-attribute=format]
 void set_message_by_errcode(va_list ap) { set_message(&a, ap); }
                                                             ^

I believe the warning is spurious, since there's no way you could construct a
valid printf format attribute for set_message_by_errcode (it doesn't take in a
string parameter).

This holds for both C and C++.

atum17:~> gcc -v
Using built-in specs.
COLLECT_GCC=/usr/bin/gcc
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='Debian 7.2.0-1'
--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 --enable-default-pie
--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 7.2.0 (Debian 7.2.0-1)