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Date: Tue, 23 Aug 2011 01:03:14 +0100 From: Al Viro <viro@...IV.linux.org.uk> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: "H. Peter Anvin" <hpa@...or.com>, Andrew Lutomirski <luto@....edu>, Borislav Petkov <bp@...64.org>, Ingo Molnar <mingo@...nel.org>, "user-mode-linux-devel@...ts.sourceforge.net" <user-mode-linux-devel@...ts.sourceforge.net>, Richard Weinberger <richard@....at>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "mingo@...hat.com" <mingo@...hat.com> Subject: Re: [uml-devel] SYSCALL, ptrace and syscall restart breakages (Re: [RFC] weird crap with vdso on uml/i386) On Mon, Aug 22, 2011 at 04:27:51PM -0700, Linus Torvalds wrote: > So I think the "let's fix the vdso case for sysenter" + "let's remove > the 32-bit syscall vdso" is the right solution. If somebody has > hardcoded syscall instructions, or generates them dynamically with > some JIT, that's their problem. We'll continue to support it as well > as we ever have (read: "almost nobody will ever notice"). Umm... Maybe, but I really wonder if it would be better to do this: * check if %ecx is the right one for vdso32 entry. If it isn't, act as we act now (and possibly warn). If it is, increment it by 4. * slap 0x90, 0x90, 0xcd, 0x80 right after that syscall insn - i.e. nop/nop/int 0x80. Followed by what we currently do there. Those who do syscall insn in 32bit mode outside of vdso will get what they currently get. __kernel_vsyscall() will keep working and do that without restart problems. And the price is comparison + branch not taken + addition for that path... -- 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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