Date: Sun, 16 Sep 2001 11:26:33 -0700 (PDT) From: John Polstra <jdp@polstra.com> To: stable@freebsd.org Subject: Re: sys/i386/i386/identcpu.c bugfix Message-ID: <200109161826.f8GIQXu77119@vashon.polstra.com> In-Reply-To: <200109151906.f8FJ6Kk74842@vashon.polstra.com> References: <20010905160610.U1222-100000@earth.serd.org> <200109151906.f8FJ6Kk74842@vashon.polstra.com>
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In article <200109151906.f8FJ6Kk74842@vashon.polstra.com>,
John Polstra <jdp@polstra.com> wrote:
>
> About your patch: I made a different version which I think is slightly
> better, because it specifies the memory clobbers more specifically.
> It's simpler, too. I checked the compiler's assembly language output,
> and it looks like it's doing the right thing. Could you please give
> it a try? Note, I removed the clobber of "cc" because the Intel
> book says that no flags are affected by the CPUID instruction.
>
> This is relative to today's -stable:
>
> Index: identcpu.c
> ===================================================================
> RCS file: /home/ncvs/src/sys/i386/i386/identcpu.c,v
> retrieving revision 1.80.2.6
> diff -c -r1.80.2.6 identcpu.c
> *** identcpu.c 2001/07/19 09:12:07 1.80.2.6
> --- identcpu.c 2001/09/15 19:04:23
> ***************
> *** 114,127 ****
> do_cpuid(u_int ax, u_int *p)
> {
> __asm __volatile(
> ! ".byte 0x0f, 0xa2;"
> ! "movl %%eax, (%2);"
> ! "movl %%ebx, 4(%2);"
> ! "movl %%ecx, 8(%2);"
> ! "movl %%edx, 12(%2);"
> ! : "=a" (ax)
> : "0" (ax), "S" (p)
> - : "bx", "cx", "dx"
> );
> }
>
> --- 114,122 ----
> do_cpuid(u_int ax, u_int *p)
> {
> __asm __volatile(
> ! ".byte 0x0f, 0xa2"
> ! : "=a" (p[0]), "=b" (p[1]), "=c" (p[2]), "=d" (p[3])
> : "0" (ax), "S" (p)
> );
> }
>
Oops, this can be simplified further, because it is no longer
necessary to specify %esi as an input. Here's a new patch:
Index: identcpu.c
===================================================================
RCS file: /home/ncvs/src/sys/i386/i386/identcpu.c,v
retrieving revision 1.80.2.6
diff -c -r1.80.2.6 identcpu.c
*** identcpu.c 2001/07/19 09:12:07 1.80.2.6
--- identcpu.c 2001/09/16 18:25:00
***************
*** 114,127 ****
do_cpuid(u_int ax, u_int *p)
{
__asm __volatile(
! ".byte 0x0f, 0xa2;"
! "movl %%eax, (%2);"
! "movl %%ebx, 4(%2);"
! "movl %%ecx, 8(%2);"
! "movl %%edx, 12(%2);"
! : "=a" (ax)
! : "0" (ax), "S" (p)
! : "bx", "cx", "dx"
);
}
--- 114,122 ----
do_cpuid(u_int ax, u_int *p)
{
__asm __volatile(
! ".byte 0x0f, 0xa2"
! : "=a" (p[0]), "=b" (p[1]), "=c" (p[2]), "=d" (p[3])
! : "0" (ax)
);
}
John
--
John Polstra jdp@polstra.com
John D. Polstra & Co., Inc. Seattle, Washington USA
"Disappointment is a good sign of basic intelligence." -- Chögyam Trungpa
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