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Re: [Xen-devel] [PATCH] x86 emulation: fix bswap
| To: | "Petersson, Mats" <Mats.Petersson@xxxxxxx>, Jan Beulich <jbeulich@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx> |
|---|---|
| Subject: | Re: [Xen-devel] [PATCH] x86 emulation: fix bswap |
| From: | Keir Fraser <keir@xxxxxxxxxxxxx> |
| Date: | Thu, 15 Feb 2007 11:54:27 +0000 |
| Delivery-date: | Thu, 15 Feb 2007 03:53:57 -0800 |
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| Thread-topic: | [Xen-devel] [PATCH] x86 emulation: fix bswap |
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On 15/2/07 11:46, "Petersson, Mats" <Mats.Petersson@xxxxxxx> wrote:
> I just wrote a little bit of code to test it:
> int x = 0x12345678;
> __asm__(".byte 0x66; bswap %0": "=r"(x): "0"(x))
> printf("x=%x", x);
>
> Prints 12340000, so the data is "zerod". (and it looks like the code
> generated by gcc is correct!).
Same behaviour as on an Intel CPU. I am quite inclined to do that directly
in the emulator, with a comment explaining why, rather than do an undefined
operation. That just seems unnecessarily scary. Direct 32- and 64-bit BSWAP
is okay though and does reduce the code size.
-- Keir
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