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Date: Sat, 10 Jan 2015 15:23:36 +0100
From: Borislav Petkov <bp@alien8.de>
To: Denys Vlasenko <vda.linux@googlemail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Frederic Weisbecker <fweisbec@gmail.com>, X86 ML <x86@kernel.org>,
        Alexei Starovoitov <ast@plumgrid.com>, Will Drewry <wad@chromium.org>,
        Kees Cook <keescook@chromium.org>
Subject: Re: [PATCH 3/4] x86: open-code register save/restore in
 trace_hardirqs thunks
Message-ID: <20150110142336.GC12218@pd.tnic>
References: <1420734315-30943-1-git-send-email-dvlasenk@redhat.com>
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 <20150109121950.GD13637@pd.tnic>
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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.
--