From: "H. Peter Anvin" <hpa@kernel.org>
To: Jakub Jelinek <jakub@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Arjan van de Ven <arjan@infradead.org>,
Roland McGrath <roland@redhat.com>,
torvalds@linux-foundation.org, linux-kernel@vger.kernel.org,
linux-arch@vger.kernel.org, x86@kernel.org
Subject: Re: [PATCH 1/2] UNREACHABLE() macro
Date: Sun, 13 Sep 2009 13:10:45 -0700 [thread overview]
Message-ID: <4AAD51C5.3050803@kernel.org> (raw)
In-Reply-To: <20090912063840.GR14664@tyan-ft48-01.lab.bos.redhat.com>
On 09/11/2009 11:38 PM, Jakub Jelinek wrote:
>>>
>>> That works for flags, but not for the presence of builtin functions.
>>> You can't even just try compiling something, since it will turn into an
>>> ordinary function if not present... not obvious until link.
>>
>> Use -Wall -Werror and if the compiler doesn't know about
>> __builtin_unreachable() it will error out.
>
> Yeah, e.g. checking exit status of:
> echo '__attribute__((noreturn)) void foo (void) { asm volatile ("" : : : "memory"); __builtin_unreachable (); }' | gcc -S -O2 -W -Wall -Werror -xc - -o /dev/null > /dev/null 2>/dev/null
> works.
>
OK, that makes sense... although perhaps it would be cleaner to use
something that could work for other builtins.
One advantage of using "nm" would be that it could answer the general
question "does this version of gcc support __builtin_X() without
resorting to libgcc", which matters quite a bit for functions like
__builtin_ctzl() and so on.
-hpa
next prev parent reply other threads:[~2009-09-13 20:16 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-09-10 1:59 [PATCH 0/2] __builtin_unreachable Roland McGrath
2009-09-10 2:00 ` [PATCH 1/2] UNREACHABLE() macro Roland McGrath
2009-09-11 20:45 ` Andrew Morton
2009-09-11 20:59 ` Kyle McMartin
2009-09-11 20:59 ` Kyle McMartin
2009-09-11 21:55 ` Roland McGrath
2009-09-12 3:49 ` Arjan van de Ven
2009-09-12 4:43 ` H. Peter Anvin
2009-09-12 5:30 ` Arjan van de Ven
2009-09-12 5:30 ` Arjan van de Ven
2009-09-12 5:52 ` Andrew Morton
2009-09-12 6:38 ` Jakub Jelinek
2009-09-12 6:38 ` Jakub Jelinek
2009-09-13 20:10 ` H. Peter Anvin [this message]
2009-09-10 2:01 ` [PATCH 2/2] x86: BUG(): use UNREACHABLE() Roland McGrath
2009-09-10 2:01 ` Roland McGrath
2009-09-10 4:42 ` [PATCH 0/2] __builtin_unreachable Américo Wang
2009-09-10 6:42 ` H. Peter Anvin
2009-09-10 6:13 ` Jakub Jelinek
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