linux-kernel - Re: [PATCH 13/18] x86 vDSO: ia32 sysenter

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Message-Id: <1195603534.6352.231.camel@bodhitayantram.eng.vmware.com>
Date:	Tue, 20 Nov 2007 16:05:34 -0800
From:	Zachary Amsden <zach@...are.com>
To:	Roland McGrath <roland@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 13/18] x86 vDSO: ia32 sysenter_return

On Mon, 2007-11-19 at 14:06 -0800, Roland McGrath wrote:
> This changes the 64-bit kernel's support for the 32-bit sysenter
> instruction to use stored fields rather than constants for the
> user-mode return address, as the 32-bit kernel does.  This adds a
> sysenter_return field to struct thread_info, as 32-bit has.  There
> is no observable effect from this yet.  It makes the assembly code
> independent of the 32-bit vDSO mapping address, paving the way for
> making the vDSO address vary as it does on the 32-bit kernel.

I hope you won't carry the dependency of COMPAT_VDSO over to 64-bit when
that happens.

> @@ -104,7 +103,7 @@ ENTRY(ia32_sysenter_target)
>  	pushfq
>  	CFI_ADJUST_CFA_OFFSET 8
>  	/*CFI_REL_OFFSET rflags,0*/
> -	movl	$VSYSCALL32_SYSEXIT, %r10d
> +	movl	8*3-THREAD_SIZE+threadinfo_sysenter_return(%rsp), %r10d

8*3-THREAD_SIZE is not very intuitive.  Can you add a comment on the
math?

Zach

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