From: "Jan Beulich" <jbeulich@suse.com>
To: andrew.cooper3@citrix.com, xen-devel@lists.xen.org
Subject: Re: [PATCH] x86/alternatives: Force inline stac() and clac()
Date: Mon, 18 Aug 2014 21:40:05 +0100 [thread overview]
Message-ID: <53F272B502000078000BABA7@mail.emea.novell.com> (raw)
In-Reply-To: <1408378137-16138-1-git-send-email-andrew.cooper3@citrix.com>
>>> Andrew Cooper <andrew.cooper3@citrix.com> 08/18/14 6:16 PM >>>
>In this case, we know better than the compiler.
>
>gcc 4.7 (Debian Wheezy) chooses to create translation-unit-local functions
>(even for non-debug builds) named stac() and clac(), and calls them.
>
>$ objdump -d xen-syms | grep -c "<stac>:"
>6
>
>$ objdump -d xen-syms | grep -o "callq [0-9a-f]\+ <stac>" | uniq -c
>5 callq ffff82d0801166c9 <stac>
>20 callq ffff82d08015ef99 <stac>
>4 callq ffff82d080165169 <stac>
>8 callq ffff82d080188cb9 <stac>
>3 callq ffff82d080228779 <stac>
>4 callq ffff82d08022c5c9 <stac>
>
>Forcing always_inline removes these functions, and replaces each of the callqs
>with the expected 3byte nops.
I'm fine putting the patch in, but isn't this a compiler bug? Creating a 5-byte
call instruction instead of a 3-byte inline expansion should even preclude out
of line placement under -Os (which otherwise is the most likely reason for
functions not getting inlined).
Jan
next prev parent reply other threads:[~2014-08-18 20:40 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-18 16:08 [PATCH] x86/alternatives: Force inline stac() and clac() Andrew Cooper
2014-08-18 20:40 ` Jan Beulich [this message]
2014-08-18 23:21 ` Andrew Cooper
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