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Date: Fri, 15 Feb 2008 00:19:17 +0100 From: Ingo Molnar <mingo@...e.hu> To: pageexec@...email.hu Cc: Jakub Jelinek <jakub@...hat.com>, Sam Ravnborg <sam@...nborg.org>, Arjan van de Ven <arjan@...radead.org>, linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org, Thomas Gleixner <tglx@...utronix.de>, "H. Peter Anvin" <hpa@...or.com> Subject: Re: [x86.git#mm] stack protector fixes, vmsplice exploit * pageexec@...email.hu <pageexec@...email.hu> wrote: > On 14 Feb 2008 at 17:35, Jakub Jelinek wrote: > > > Where do you see a mispredicted branch? > > try it with -Os (gentoo gcc 4.2.2): > > 0000000000000000 <foo>: > 0: 48 83 ec 58 sub $0x58,%rsp > 4: 65 48 8b 04 25 28 00 00 00 mov %gs:0x28,%rax > d: 48 89 44 24 48 mov %rax,0x48(%rsp) > 12: 31 c0 xor %eax,%eax > 14: 48 89 e7 mov %rsp,%rdi > 17: e8 00 00 00 00 callq 1c <foo+0x1c> 18: R_X86_64_PC32 > bar+0xfffffffffffffffc > 1c: 48 8b 54 24 48 mov 0x48(%rsp),%rdx > 21: 65 48 33 14 25 28 00 00 00 xor %gs:0x28,%rdx > 2a: b8 06 00 00 00 mov $0x6,%eax > 2f: 74 05 je 36 <foo+0x36> > 31: e8 00 00 00 00 callq 36 <foo+0x36> 32: R_X86_64_PC32 > __stack_chk_fail+0xfffffffffffffffc > 36: 48 83 c4 58 add $0x58,%rsp > 3a: c3 retq ah, that's what my kernel uses too - and CONFIG_CC_OPTIMIZE_FOR_SIZE=y is the default for Fedora too. hm, especially those big addressing mode mov's and xor's look rather nasty. Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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