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Date: Thu, 09 Aug 2012 09:46:10 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: linux-kernel@...r.kernel.org,
"H. Peter Anvin" <hpa@...ux.intel.com>
Cc: 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
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!
-- Steve
On Tue, 2012-08-07 at 15:38 -0400, Steven Rostedt wrote:
> From: Steven Rostedt <srostedt@...hat.com>
>
> If the kernel is compiled with gcc 4.6.0 which supports -mfentry,
> then use that instead of mcount.
>
> With mcount, frame pointers are forced with the -pg option and we
> get something like:
>
> <can_vma_merge_before>:
> 55 push %rbp
> 48 89 e5 mov %rsp,%rbp
> 53 push %rbx
> 41 51 push %r9
> e8 fe 6a 39 00 callq ffffffff81483d00 <mcount>
> 31 c0 xor %eax,%eax
> 48 89 fb mov %rdi,%rbx
> 48 89 d7 mov %rdx,%rdi
> 48 33 73 30 xor 0x30(%rbx),%rsi
> 48 f7 c6 ff ff ff f7 test $0xfffffffff7ffffff,%rsi
>
> With -mfentry, frame pointers are no longer forced and the call looks
> like this:
>
> <can_vma_merge_before>:
> e8 33 af 37 00 callq ffffffff81461b40 <__fentry__>
> 53 push %rbx
> 48 89 fb mov %rdi,%rbx
> 31 c0 xor %eax,%eax
> 48 89 d7 mov %rdx,%rdi
> 41 51 push %r9
> 48 33 73 30 xor 0x30(%rbx),%rsi
> 48 f7 c6 ff ff ff f7 test $0xfffffffff7ffffff,%rsi
>
> This adds the ftrace hook at the beginning of the function before a
> frame is set up, and allows the function callbacks to be able to access
> parameters. As kprobes now can use function tracing (at least on x86)
> this speeds up the kprobe hooks that are at the beginning of the
> function.
>
> Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> Cc: Andi Kleen <andi@...stfloor.org>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
(change log kept the same)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index c70684f..bbbf5d8 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -36,6 +36,7 @@ config X86
select HAVE_KRETPROBES
select HAVE_OPTPROBES
select HAVE_FTRACE_MCOUNT_RECORD
+ select HAVE_FENTRY if X86_64
select HAVE_C_RECORDMCOUNT
select HAVE_DYNAMIC_FTRACE
select HAVE_FUNCTION_TRACER
diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
index a6cae0c..9a25b52 100644
--- a/arch/x86/include/asm/ftrace.h
+++ b/arch/x86/include/asm/ftrace.h
@@ -35,7 +35,11 @@
#endif
#ifdef CONFIG_FUNCTION_TRACER
-#define MCOUNT_ADDR ((long)(mcount))
+#ifdef CC_USING_FENTRY
+# define MCOUNT_ADDR ((long)(__fentry__))
+#else
+# define MCOUNT_ADDR ((long)(mcount))
+#endif
#define MCOUNT_INSN_SIZE 5 /* sizeof mcount call */
#ifdef CONFIG_DYNAMIC_FTRACE
@@ -46,6 +50,7 @@
#ifndef __ASSEMBLY__
extern void mcount(void);
extern atomic_t modifying_ftrace_code;
+extern void __fentry__(void);
static inline unsigned long ftrace_call_adjust(unsigned long addr)
{
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 38308fa..a698521 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -68,10 +68,18 @@
.section .entry.text, "ax"
#ifdef CONFIG_FUNCTION_TRACER
+
+#ifdef CC_USING_FENTRY
+# define function_hook __fentry__
+#else
+# define function_hook mcount
+#endif
+
#ifdef CONFIG_DYNAMIC_FTRACE
-ENTRY(mcount)
+
+ENTRY(function_hook)
retq
-END(mcount)
+END(function_hook)
/* skip is set if stack has been adjusted */
.macro ftrace_caller_setup skip=0
@@ -84,7 +92,11 @@ END(mcount)
movq RIP(%rsp), %rdi
subq $MCOUNT_INSN_SIZE, %rdi
/* Load the parent_ip into the second parameter */
+#ifdef CC_USING_FENTRY
+ movq SS+16(%rsp), %rsi
+#else
movq 8(%rbp), %rsi
+#endif
.endm
ENTRY(ftrace_caller)
@@ -177,7 +189,8 @@ END(ftrace_regs_caller)
#else /* ! CONFIG_DYNAMIC_FTRACE */
-ENTRY(mcount)
+
+ENTRY(function_hook)
cmpl $0, function_trace_stop
jne ftrace_stub
@@ -199,7 +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
@@ -207,7 +224,7 @@ trace:
MCOUNT_RESTORE_FRAME
jmp ftrace_stub
-END(mcount)
+END(function_hook)
#endif /* CONFIG_DYNAMIC_FTRACE */
#endif /* CONFIG_FUNCTION_TRACER */
@@ -215,9 +232,14 @@ END(mcount)
ENTRY(ftrace_graph_caller)
MCOUNT_SAVE_FRAME
+#ifdef CC_USING_FENTRY
+ leaq SS+16(%rsp), %rdi
+ movq $0, %rdx /* No framepointers needed */
+#else
leaq 8(%rbp), %rdi
- movq RIP(%rsp), %rsi
movq (%rbp), %rdx
+#endif
+ movq RIP(%rsp), %rsi
subq $MCOUNT_INSN_SIZE, %rsi
call prepare_ftrace_return
diff --git a/arch/x86/kernel/x8664_ksyms_64.c b/arch/x86/kernel/x8664_ksyms_64.c
index 9796c2f..643b236 100644
--- a/arch/x86/kernel/x8664_ksyms_64.c
+++ b/arch/x86/kernel/x8664_ksyms_64.c
@@ -13,9 +13,13 @@
#include <asm/ftrace.h>
#ifdef CONFIG_FUNCTION_TRACER
-/* mcount is defined in assembly */
+/* mcount and __fentry__ are defined in assembly */
+#ifdef CC_USING_FENTRY
+EXPORT_SYMBOL(__fentry__);
+#else
EXPORT_SYMBOL(mcount);
#endif
+#endif
EXPORT_SYMBOL(__get_user_1);
EXPORT_SYMBOL(__get_user_2);
--
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