Re: [PATCH 2/2] remove NORETURN from function pointers

>> ---
>>
>> __attribute__((noreturn)) is, according to the GCC documentation, about
>> two things: code generation (performance, really) and warnings.
>>
>> On the warnings-side, we need to keep the code warning-free for
>> compilers who doesn't support noreturn anyway, so hiding potential
>> warnings through this mechanism is probably not a good idea in the
>> first place.
>
> [Your justification text would almost certainly be useful as part of the
> commit message itself, and should go there.]

> If I understand you correctly, the problem is that there are actually
> three classes of compilers:
>
>  1. Ones which understand some NORETURN syntax for both functions and
>     function pointers, and correctly trace returns through both (e.g.,
>     gcc).
>
>  2. Ones which understand some NORETURN syntax for just functions, and
>     complain about it on function pointers. We currently turn off
>     NORETURN for these compilers (from your commit message, MSVC,
>     for example).
>
>  3. Ones which have no concept of NORETURN at all.
>
> I think the right solution to turn on NORETURN for (2) is to split it
> into two cases: NORETURN and NORETURN_PTR. Gcc platforms can define both
> identically, platforms under (2) above can define NORETURN_PTR as empty,
> and (3) will keep both off.

> I do have to wonder, though. What do compilers that fall under (2) do
> with calls to function pointers from NORETURN functions? Do they assume
> they don't return, or that they do? Or do they not check that NORETURN
> functions actually don't return?
>
> I.e., what does this program do under MSVC:
>
> #include <stdlib.h>
> void (*exit_fun)(int) = exit;
> static void die(void) __attribute__((__noreturn__));
> static void die(void) { exit_fun(1); }
> int main(void) { die(); }