linux-kernel - Re: [RFC PATCH 4/4] ftrace/x86: Add support for -mfentry to x86

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Date:	Thu, 09 Aug 2012 09:48:43 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	linux-kernel@...r.kernel.org
Cc:	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [RFC PATCH 4/4] ftrace/x86: Add support for -mfentry to x86_64

On Thu, 2012-08-09 at 09:46 -0400, Steven Rostedt wrote:
> Peter and Masami
> 
> During my final tests, I found that this change breaks the
> !DYNAMIC_FTRACE config. That is, when we don't do the run-time updates
> of mcount calls to nops, the compiler will use fentry but the code still
> uses mcount.
> 
> I fixed this in the patch below. But as you two have acked and reviewed
> it, I can't add your tags if I have changed the code. Can you ack/review
> it again.
> 
> Thanks!
> 

This is the changes that were made against the original patch:

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 2add3bb..a698521 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -68,18 +68,19 @@
 	.section .entry.text, "ax"
 
 #ifdef CONFIG_FUNCTION_TRACER
-#ifdef CONFIG_DYNAMIC_FTRACE
 
 #ifdef CC_USING_FENTRY
-ENTRY(__fentry__)
-	retq
-END(__fentry__)
+# define function_hook	__fentry__
 #else
-ENTRY(mcount)
-	retq
-END(mcount)
+# define function_hook	mcount
 #endif
 
+#ifdef CONFIG_DYNAMIC_FTRACE
+
+ENTRY(function_hook)
+	retq
+END(function_hook)
+
 /* skip is set if stack has been adjusted */
 .macro ftrace_caller_setup skip=0
 	MCOUNT_SAVE_FRAME \skip
@@ -188,7 +189,8 @@ END(ftrace_regs_caller)
 
 
 #else /* ! CONFIG_DYNAMIC_FTRACE */
-ENTRY(mcount)
+
+ENTRY(function_hook)
 	cmpl $0, function_trace_stop
 	jne  ftrace_stub
 
@@ -210,7 +212,11 @@ trace:
 	MCOUNT_SAVE_FRAME
 
 	movq RIP(%rsp), %rdi
+#ifdef CC_USING_FENTRY
+	movq SS+16(%rsp), %rsi
+#else
 	movq 8(%rbp), %rsi
+#endif
 	subq $MCOUNT_INSN_SIZE, %rdi
 
 	call   *ftrace_trace_function
@@ -218,7 +224,7 @@ trace:
 	MCOUNT_RESTORE_FRAME
 
 	jmp ftrace_stub
-END(mcount)
+END(function_hook)
 #endif /* CONFIG_DYNAMIC_FTRACE */
 #endif /* CONFIG_FUNCTION_TRACER */
 


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