On 20/04/17 11:57 +0200, Florian Weimer wrote:
On 04/20/2017 11:52 AM, Jonathan Wakely wrote:
On 20/04/17 11:43 +0200, Florian Weimer wrote:
On 04/20/2017 11:25 AM, Jonathan Wakely wrote:
I mean, with -pedantic-errors we already error on void * arighmetics
or function pointer arithmetics. If std::atomic<void*> would use
the void * arithmetics, it would also reject it. Or does it
use integer
arithmetics instead?
No, it does it on void*, but the __atomic built-ins still perform that
arithmetic even with -pedantic-errors.
sizeof is not defined for the relevant types, either, and already
triggers a warning by default:
t.cc:25:58: warning: invalid application of ‘sizeof’ to a void
type [-Wpointer-arith]
_M_type_size(ptrdiff_t __d) const { return __d * sizeof(_PTp); }
That could be easily avoided if we care about supporting arithmetic on
std::atomic<void*>.
I think the actual problem here is the suppression of warnings
from system headers.
The atomic built-ins still don't warn even with -Wsystem-headers
Sorry, this is what I meant: -pedantic-errors does not catch this case
due to the system header warning suppression. Otherwise, with the
current std::atomic implementation, -pedantic-errors would already
disable the extension on std::atomic alongside with the extension on
built-in pointer types, due to the use of sizeof in the definition of
_M_type_size.
Ah yes, you're right.
Yet another case where warning suppression in system headers hurts the
library's ability to give diagnostics. We can't warn about using
incomplete types in std::unique_ptr because the -Wdelete-incomplete
warning gets suppressed, and the interaction of #pragma GCC diagnostic
with -Wsystem-headers is ... interesting. We need a way to enable
warnings for specific blocks of code, to say "do not suppress warnings
here, even though it's in a system header".
