Re: [tip:x86/mm] x86, mm: Use a bitfield to mask nuisance get_user() warnings
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- Subject: Re: [tip:x86/mm] x86, mm: Use a bitfield to mask nuisance get_user() warnings
- From: "H. Peter Anvin" <hpa@xxxxxxxxx>
- Date: Mon, 11 Feb 2013 23:12:49 -0800
- Cc: Ingo Molnar <mingo@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Jamie Lokier <jamie@xxxxxxxxxxxxx>, ville.syrjala@xxxxxxxxxxxxxxx, Borislav Petkov <bp@xxxxxxxxx>, Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, linux-tip-commits@xxxxxxxxxxxxxxx, "H.J. Lu" <hjl.tools@xxxxxxxxx>
- In-reply-to: <CA+55aFzmWfOQzVMPJUah3oEsn-aaeN5qtO=7P3MQUfLZmEFJZA@mail.gmail.com>
- User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130110 Thunderbird/17.0.2
Just to be sure, I re-ran the comparison using gcc 4.6.3 instead of gcc
4.7.2. With gcc 4.6.3 I consistently get a few hundred bytes longer
with the bitfield variant than with the pre-get_user() baseline.
I looked at some of the diffed disassembly, and the differences seem to
be in the code generated downstream of __get_user_1 and __get_user_2,
which I guess is to be expected, mostly in the form of padding.
Annoyingly enough in *both* cases I found unnecessary instructions like:
+c12f6fbb: 0f b7 d2 movzwl %dx,%edx
-hpa
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