Al Viro wrote:
> On Wed, Jul 25, 2007 at 09:56:12AM -0700, Linus Torvalds wrote:
>
>> On Tue, 24 Jul 2007, David Miller wrote:
>>
>>> From: Jeremy Fitzhardinge <[EMAIL PROTECTED]>
>>> Date: Tue, 24 Jul 2007 23:24:55 -0700
>>>
>>>
>>>> H. Peter Anvin wrote:
>>>>
>>>>> How far back was __builtin_trap() supported?
>>>>>
>>>> I think its relatively recent, but it might be within our supported
>>>> compiler window.
>>>>
>>> I'm pretty sure it is.
>>>
>> .. and I'm pretty sure it's immaterial.
>>
>> We don't just do the "ud2" instruction - we also do the file and line
>> number information after it. Which means that __builtin_trap() is useless.
>>
>> So we might as well keep the loop, since both are two-byte instructions
>> that tell gcc that it will never continue.
>>
>
> Umm... Actually, we might be able to do something like
> {
> l: __builtin_trap();
> static struct ... v __attribute__((section(...))) = { &&l, n, file };
> }
>
> except that it would need block-local labels and those are ugly (so's
> &&<label>, while we are at it)...
>
I couldn't get it to work. It would be nice, because it would more or
less eliminate the need for asm in setting up BUGs - particularly the
nasty asm setting up the structure.
But it just doesn't work. The label &&l ends up pointing to is not
anywhere near the __builtin_trap instruction; I found it tended to point
to the start of the function prologue.
I reported it as a gcc bug, but they refused to hear of it. Details at
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29305
J
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