On Wed, 5 Jun 2019 11:49:21 -0500 Segher Boessenkool <seg...@kernel.crashing.org> wrote:
> On Wed, Jun 05, 2019 at 02:25:59PM +0100, Jozef Lawrynowicz wrote: > > I'm assuming it would not be valid to modify the behaviour of __extension__ > > so it can be placed within a declaration, and not just at the > > beginning. However, there is minimal documentation on this keyword (it does > > not > > state that it can be used in declarations, even though it can), so I wonder > > what the "rules" are. > > The documentation says > > '-pedantic' and other options cause warnings for many GNU C extensions. > You can prevent such warnings within one expression by writing > '__extension__' before the expression. '__extension__' has no effect > aside from this. > > It's not clear to me why you cannot simply put __extension__ earlier in > your case? If I am modifying tests on an individual basis, then indeed I can put __extension__ earlier in the declaration and it fixes the issue. But for a fix within the compiler to prevent having to modify individual tests, I could add __extension__ to the beginning of the macro - but the macro may not end up at the beginning of a declaration in the source code. For example, say __SIZE_TYPE__ now expands to "__extension__ __int20 unsigned", then the following usage of __SIZE_TYPE__ would be ok, as __extension__ is at the beginning of the declaration: > __SIZE_TYPE__ size; But the following would emit an error, because __extension__ is not at the beginning of the declaration: > typedef __SIZE_TYPE__ size_t; I'm mainly just wondering if a change to the compiler to allow the usage of __extension__ within a declaration would be allowed. However since there are many contexts where usage of a type such as __SIZE_TYPE__ is valid, but where __extension__ preceding the type wouldn't be valid, this is probably not worth exploring.. I'm aware of some different ways that the tests can be fixed up to prevent the ISO C errors caused by -pedantic-errors. I'm currently thinking the best way to fix these issues in the testsuite might be to implement a directive such as "dg-prune-options". This directive can then prune "-pedantic-errors" from the options to be passed to GCC when some specified condition (e.g. -mlarge is in the opt list) is matched. This would at least avoid having to re-jig tests to get the __extension__ keyword into the right places, as the dg-prune-options can just be added to the problematic tests. Thanks, Jozef
