https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107802
Bug ID: 107802
Summary: -Wsuggest-attribute=format ignores
[[gnu::format(...)]]
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: adam.f.badura at gmail dot com
Target Milestone: ---
I checked the issue with GCC 10.2 and trunk as on Compiler Explorer using
arguments
-std=c++17 -O3 -Wall -Wextra -Wpedantic -Wsuggest-attribute=format
The following code (https://godbolt.org/z/qP91h5Knv):
#include <cstdarg>
#include <cstdio>
#include <cstdlib>
__attribute__((format(printf, 4, 5))) [[noreturn]] void raise(
[[maybe_unused]] const char* const file,
[[maybe_unused]] const unsigned line,
[[maybe_unused]] const char* const condition,
const char* assertionMessage,
...)
{
std::fprintf(stderr, "*** Assertion message: ");
va_list args;
va_start(args, assertionMessage);
std::vfprintf(stderr, assertionMessage, args);
va_end(args);
std::fprintf(stderr, "\n");
std::abort();
}
passes fine.
However, if we replace
__attribute__((format(printf, 4, 5)))
with
[[gnu::format(printf, 4, 5)]]
a warning shows up (https://godbolt.org/z/oecjj4Tzv):
<source>: In function 'void raise(const char*, unsigned int, const char*,
const char*, ...)':
<source>:15:49: warning: function 'void raise(const char*, unsigned int, const
char*, const char*, ...)' might be a candidate for
'gnu_printf' format attribute [-Wsuggest-attribute=format]
15 | std::vfprintf(stderr, assertionMessage, args);
| ^
My overall experience is that the [[gnu::...]] syntax for attributes doesn't
behave the same as the __attribute__((...)) syntax. Not only it seems to be
more limited to where we can place it (this is up to C++, not GCC) but also it
seems attributes provided this way are more likely to be more or less ignored.
However, this is the first time I caught the issue so clearly.
