Martin Storsjö wrote:
On Fri, 17 Feb 2023, Christian Franke wrote:
When compiling this on MSYS2 UCRT64 with current
mingw-w64-ucrt-x86_64-gcc 12.2.0-10, gcc and g++ results differ:
#include <stdint.h>
#include <stdio.h>
#if !(defined(_UCRT) && !__USE_MINGW_ANSI_STDIO)
#warning unexpected configuration
#endif
void f(size_t s, uint64_t u)
{
// gcc: No warning
// g++: "unknown conversion type character 'z' ..."
printf("%zu", s);
// gcc: "format '%u' expects argument of type 'unsigned int', ..."
// g++: No warning
printf("%I64u", u);
}
This shows that gcc defaults to format 'gnu_printf' but g++ defaults
to format 'ms_printf'.
Is this difference intentional, a MSYS2 packaging issue (i.e. wrong
build parameters, incomplete local patch, ...) or a GCC upstream bug?
Would not be a problem if gcc/g++ would allow to override this
attribute for its builtins.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95130
That's indeed weird. It looks to me like this is possibly another
case/variant of the linked bug.
By preprocessing the source file with -E, it looks to me like the
printf function does end up declared with gnu_printf format in both
cases anyway - so with that in mind, it should be consistent - but
perhaps intricacies of that bug makes it only happen in one language
mode but not in the other one.
The test below shows that the __attribute__ ((__nonnull__ (1))) from the
expanded prototype makes a difference. If specified, the default format
ms_printf is overridden, but only if gcc is used. The builtin is still
active for code generation as the printf() -> puts() optimization is
still done.
#ifdef __cplusplus
extern "C" {
#endif
typedef unsigned long long uint64_t;
typedef unsigned long long size_t;
__attribute__((__format__(gnu_printf,1,2)))
#ifdef NN
// gcc: gnu_printf, g++: ms_printf
__attribute__ ((__nonnull__ (1)))
#else
// gcc/g++: ms_printf
#endif
int __attribute__((__cdecl__)) printf(const char * __restrict__
_Format,...);
#ifdef __cplusplus
}
#endif
void f(size_t s, uint64_t u)
{
printf("%zu", s);
printf("%I64u", u);
printf("Text\n"); // always generates puts("Text");
}
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