From: "Américo Wang" <xiyou.wangcong@gmail.com>
To: Roland McGrath <roland@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Jakub Jelinek <jakub@redhat.com>,
linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
x86@kernel.org
Subject: Re: [PATCH 0/2] __builtin_unreachable
Date: Thu, 10 Sep 2009 12:42:26 +0800 [thread overview]
Message-ID: <2375c9f90909092142i58595fedod6780a7c41190f5f@mail.gmail.com> (raw)
In-Reply-To: <20090910015923.8FB628AE5F@magilla.sf.frob.com>
On Thu, Sep 10, 2009 at 9:59 AM, Roland McGrath <roland@redhat.com> wrote:
> The latest GCC has a better way than "for (;;)" to indicate that a code
> path cannot be reached due to reasons the compiler doesn't understand (such
> as code in an asm). These patches provide UNREACHABLE() as a macro to hide
> the details of this, and then use it for the BUG() macro on x86, saving
> some dead code otherwise generated.
>
> Other arch's BUG() may want to this too instead of "for (;;)" or __builtin_trap.
>
> There are numerous matches from "git grep -n 'for *(;;) *;'" but it takes
> someone who knows each bit of code to know where that means UNREACHABLE()
> and where it really wants an infinite loop.
Looks good!
Reviewed-by: WANG Cong <xiyou.wangcong@gmail.com>
Just curious, what different asm code will gcc generate for this? Comparing it
to for(;;) ? I am sorry that I don't have gcc 4.5 on hand.
Thanks!
next prev parent reply other threads:[~2009-09-10 4:42 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
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 ` Américo Wang [this message]
2009-09-10 6:42 ` [PATCH 0/2] __builtin_unreachable H. Peter Anvin
2009-09-10 6:13 ` Jakub Jelinek
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