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[Xen-devel] A question about SYSENTER/SYSEXIT in HVM guest

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Subject: [Xen-devel] A question about SYSENTER/SYSEXIT in HVM guest
From: Guofu Xiang <whxgf1984@xxxxxxxxx>
Date: Mon, 6 Apr 2009 21:11:52 +0800
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The CPU type of our server is Intel Xeon E5310, and the OS is Fedora 8. Xen 3.2 is installed by compilation. When the HVM guest is x86_32 Fedora 8, the system call is implemented by instruction - int $80h. Our debug result by gdb is as follow.
Dump of assembler code for function __kernel_vsyscall:
0xb7f87400 <__kernel_vsyscall+0>:       int    $0x80
0xb7f87402 <__kernel_vsyscall+2>:       ret   
End of assembler dump.
However, when the HVM guest is x86_64 Fedora 8, the system call is implemented by instruction - syscall. The debug result is as fellow:
Dump of assembler code for function getuid:
0x00000036e7296220 <getuid+0>:  mov    $0x66,%eax
0x00000036e7296225 <getuid+5>:  syscall
0x00000036e7296227 <getuid+7>:  retq
As far as I know, fast system call is implemented by sysenter on Intel CPU, and syscall on AMD CPU. Why the debug result is syscall, rather than sysenter?
If the HVM guest is x86_32 Fedora 8, can we set the system call implementation by sysenter? In x86_64 OS, is all system call implemented by syscall?
Thank you for your response!
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