Re: Merging feature/android

[Po Lu]

Arsen Arsenović <arsen@aarsen.me> writes:

> Po Lu <luangruo@yahoo.com> writes:
>
>> Arsen Arsenović <arsen@aarsen.me> writes:
>>
>>> Depending on how long ago that was, it might be worth reconsidering.
>>> GCC has been C++ for a decade now, for instance, so C++ compilers are
>>> likely fairly widespread.  One could make the case that using portable
>>> C++ in addition to portable C is a more portable way to do cleanups than
>>> GNU C cleanups.
>>>
>>> If still undesirable, I strongly suggest at least using GNU C cleanups.
>>> They are a decent workaround.
>>
>> GNU C cleanups only work when compiling with -fexceptions.
>
> This is not the case.  They work under all conditions, and are used to
> great effect in many C codebases.  As an example, the following:
>
>   int
>   f (void (*foo) (void))
>   {
>     __attribute__ ((cleanup (test))) int* n = g ();
>     foo ();
>   }
>
> ... generates:
>
>   f:
>         pushq   %rbx
>         xorl    %eax, %eax
>         movq    %rdi, %rbx
>         subq    $16, %rsp
>         call    g
>         movq    %rax, 8(%rsp)
>         call    *%rbx
>         leaq    8(%rsp), %rdi
>         call    test             /* cleanup */
>         addq    $16, %rsp
>         popq    %rbx
>         ret
>
> ... with -O3 -fno-exceptions.  The latter is the default for C, but I
> wanted to be explicit anyway.

I meant that they only work to handle C++ exceptions when you compile
with -fexceptions, so it is rather pointless to use it as we do now.
Without -fexceptions, that code is no different from:

f (foo)
  int (*foo) ();
{
  int *n;

  n = g ();
  foo ();
  test (fn);
}

> It is likely as widely available as cleanup attributes.  Certainly as
> widely as any supported (or many unsupported) versions of GCC are.
>
> I won't argue on the merits of the language, as that usually doesn't go
> anywhere, and the cleanup attribute seems like an accepted solution
> anyway.  Note that it's no coincidence that it is being adopted by some
> GNU projects.

The GNU Coding Standards recommend against relying on GNU C extensions
in Emacs.

> I agree that it isn't necessary.  I was just answering the question of
> what '-fexceptions' would do as someone with the know-how, because it
> was brought up.

OK, then let's not waste any more time here.  Thanks.