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Groups > linux.kernel > #1311880
| From | Borislav Petkov <bp@suse.de> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init |
| Date | 2016-01-19 02:20 +0100 |
| Message-ID | <qSt7I-vW-11@gated-at.bofh.it> (permalink) |
| References | (2 earlier) <qRFaV-v0-1@gated-at.bofh.it> <qRSUx-1gy-15@gated-at.bofh.it> <qSljR-3pb-13@gated-at.bofh.it> <qSmzg-4r1-13@gated-at.bofh.it> <qSnbY-4FZ-15@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Mon, Jan 18, 2016 at 07:51:07PM +0100, Borislav Petkov wrote:
> [45] .static_cpu_has PROGBITS ffffffff97aa655b 16ea655b
> 00000000000002df 0000000000000000 AX 0 0 1
Ok, staring at this section was wrong. I went and looked at
the .s file and now it clicked: gcc inlines those calls to
__static_cpu_has_safe of the dynamic jump target:
.loc 4 538 0
movl $125, %edi #,
call __static_cpu_has_safe #
.LBE885:
.LBE886:
.LBE914:
.loc 1 240 0
testb %al, %al # D.30157
je .L150 #,
jmp .L151 #
.L152:
.LBB915:
.LBB909:
.LBB905:
.LBB893:
.LBB892:
.loc 4 538 0
movl $154, %edi #,
call __static_cpu_has_safe #
.LBE892:
.LBE893:
.LBE905:
.loc 7 431 0
testb %al, %al # D.30157
jne .L154 #,
which turn into:
751: bf 7d 00 00 00 mov $0x7d,%edi
756: e8 00 00 00 00 callq 75b <fpu__copy+0xab>
75b: 84 c0 test %al,%al
75d: 74 a3 je 702 <fpu__copy+0x52>
75f: eb 90 jmp 6f1 <fpu__copy+0x41>
761: bf 9a 00 00 00 mov $0x9a,%edi
766: e8 00 00 00 00 callq 76b <fpu__copy+0xbb>
76b: 84 c0 test %al,%al
That's like 28 bytes in this particular case, which is 14 per call site,
on average.
So grepping through my tailored vmlinux, it has 35 entries with
X86_FEATURE_ALWAYS in .altinstructions X 14 = 490 bytes.
So yeah, we probably should do this, allyesconfig should give more
savings.
One thing I'd probably do differently is not call the throwaway section
.static_cpu_has but something like .altinstr_temporary or so and put it
after the replacement insns:
.altinstr_replacement : AT(ADDR(.altinstr_replacement) - LOAD_OFFSET) {
*(.altinstr_replacement)
*(.altinstr_temporary)
}
so that we know those instructions belong to the alternatives mechanism.
They'll get discared too, of course.
I could just as well be talking a lot of crap, it is waay too late here.
--
Regards/Gruss,
Boris.
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--
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[PATCH] x86: static_cpu_has_safe: discard dynamic check after init Brian Gerst <brgerst@gmail.com> - 2016-01-16 20:30 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Borislav Petkov <bp@suse.de> - 2016-01-16 20:40 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Brian Gerst <brgerst@gmail.com> - 2016-01-16 21:00 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Borislav Petkov <bp@suse.de> - 2016-01-17 11:40 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Brian Gerst <brgerst@gmail.com> - 2016-01-18 18:00 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Andy Lutomirski <luto@amacapital.net> - 2016-01-18 18:50 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Borislav Petkov <bp@suse.de> - 2016-01-18 19:20 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Andy Lutomirski <luto@amacapital.net> - 2016-01-18 19:30 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Borislav Petkov <bp@suse.de> - 2016-01-18 19:40 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init "H. Peter Anvin" <hpa@zytor.com> - 2016-01-18 20:50 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Borislav Petkov <bp@suse.de> - 2016-01-19 00:10 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init "H. Peter Anvin" <hpa@zytor.com> - 2016-01-19 00:20 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Borislav Petkov <bp@suse.de> - 2016-01-19 00:30 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Borislav Petkov <bp@suse.de> - 2016-01-19 15:00 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Borislav Petkov <bp@suse.de> - 2016-01-19 17:30 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Borislav Petkov <bp@suse.de> - 2016-01-20 00:20 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Andy Lutomirski <luto@amacapital.net> - 2016-01-20 00:30 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Boris Petkov <bp@suse.de> - 2016-01-20 01:00 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init "H. Peter Anvin" <hpa@zytor.com> - 2016-01-20 05:10 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Borislav Petkov <bp@suse.de> - 2016-01-20 11:40 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init "H. Peter Anvin" <hpa@zytor.com> - 2016-01-20 11:50 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Borislav Petkov <bp@suse.de> - 2016-01-21 23:20 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init "H. Peter Anvin" <hpa@zytor.com> - 2016-01-21 23:30 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Borislav Petkov <bp@suse.de> - 2016-01-22 00:00 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init "H. Peter Anvin" <hpa@zytor.com> - 2016-01-22 00:40 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init "H. Peter Anvin" <hpa@zytor.com> - 2016-01-22 00:40 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Borislav Petkov <bp@suse.de> - 2016-01-22 11:40 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Borislav Petkov <bp@suse.de> - 2016-01-18 20:00 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Borislav Petkov <bp@suse.de> - 2016-01-19 02:20 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init "H. Peter Anvin" <hpa@zytor.com> - 2016-01-19 02:40 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Borislav Petkov <bp@suse.de> - 2016-01-19 10:30 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init "H. Peter Anvin" <hpa@zytor.com> - 2016-01-20 05:10 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Brian Gerst <brgerst@gmail.com> - 2016-01-20 05:40 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init "H. Peter Anvin" <hpa@zytor.com> - 2016-01-20 05:50 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init "H. Peter Anvin" <hpa@zytor.com> - 2016-01-20 12:00 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Borislav Petkov <bp@suse.de> - 2016-01-20 12:10 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init "H. Peter Anvin" <hpa@zytor.com> - 2016-01-20 15:50 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Borislav Petkov <bp@suse.de> - 2016-01-20 12:00 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Borislav Petkov <bp@suse.de> - 2016-01-20 16:10 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init "H. Peter Anvin" <hpa@zytor.com> - 2016-01-20 16:20 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Borislav Petkov <bp@suse.de> - 2016-01-20 17:10 +0100
Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init "H. Peter Anvin" <hpa@zytor.com> - 2016-01-20 17:20 +0100
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