linux-kernel - Re: [PATCH 3/4] x86: open-code register save/restore in trace

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Message-ID: <20150110142336.GC12218@pd.tnic>
Date:	Sat, 10 Jan 2015 15:23:36 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Denys Vlasenko <vda.linux@...glemail.com>
Cc:	Denys Vlasenko <dvlasenk@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...capital.net>,
	Frederic Weisbecker <fweisbec@...il.com>,
	X86 ML <x86@...nel.org>, Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH 3/4] x86: open-code register save/restore in
 trace_hardirqs thunks

On Fri, Jan 09, 2015 at 07:54:08PM +0100, Denys Vlasenko wrote:
> In order to narrow it down, can you, instead of my patch, try
> just deleting this one line, and see whether breakage appears?

Yep, this works:

---
Index: b/arch/x86/lib/thunk_64.S
===================================================================
--- a/arch/x86/lib/thunk_64.S	2015-01-10 15:03:10.262716858 +0100
+++ b/arch/x86/lib/thunk_64.S	2015-01-10 15:12:53.502730396 +0100
@@ -47,7 +47,6 @@
 
 	/* SAVE_ARGS below is used only for the .cfi directives it contains. */
 	CFI_STARTPROC
-	SAVE_ARGS
 restore:
 	RESTORE_ARGS
 	ret
--

Bah, I see it. This nasty '$' gets forgotten a lot, maybe we should have
a check for that in some scripts :-)

Here's the fix:

---
Index: b/arch/x86/lib/thunk_64.S
===================================================================
--- a/arch/x86/lib/thunk_64.S	2015-01-10 15:18:04.418737613 +0100
+++ b/arch/x86/lib/thunk_64.S	2015-01-10 15:17:18.882736556 +0100
@@ -67,7 +67,7 @@ restore:
 	movq_cfi_restore 6*8, rdx
 	movq_cfi_restore 7*8, rsi
 	movq_cfi_restore 8*8, rdi
-	addq 9*8, %rsp
+	addq $9*8, %rsp
 	CFI_ADJUST_CFA_OFFSET -9*8
 	ret
 	CFI_ENDPROC
---

That boots!

:-D

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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