From: Laurent Vivier <Laurent.Vivier@bull.net>
Date: Thu, 25 Oct 2007 12:18:55 +0000 (+0200)
Subject: KVM: VMX: Let gcc to choose which registers to save (i386)
X-Git-Tag: v2.6.25-rc1~1138^2~187
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ff593e5abebd899b0b41c11280e2fbeff4103375;p=pandora-kernel.git

KVM: VMX: Let gcc to choose which registers to save (i386)

This patch lets GCC to determine which registers to save when we
switch to/from a VCPU in the case of intel i386.

* Original code saves following registers:

    eax, ebx, ecx, edx, edi, esi, ebp (using popa)

* Patched code:

  - informs GCC that we modify following registers
    using the clobber description:

    ebx, edi, rsi

  - doesn't save eax because it is an output operand (vmx->fail)

  - cannot put ecx in clobber description because it is an input operand,
    but as we modify it and we want to keep its value (vcpu), we must
    save it (pop/push)

  - ebp is saved (pop/push) because GCC seems to ignore its use the clobber
    description.

  - edx is saved (pop/push) because it is reserved by GCC (REGPARM) and
    cannot be put in the clobber description.

  - line "mov (%%esp), %3 \n\t" has been removed because %3
    is ecx and ecx is restored just after.

Signed-off-by: Laurent Vivier <Laurent.Vivier@bull.net>
Signed-off-by: Avi Kivity <avi@qumranet.com>
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