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ftrace/x86: Add support for -mfentry to x86_64

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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.

Link: http://lkml.kernel.org/r/20120807194100.130477900@goodmis.org

Acked-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt 2011-02-09 13:32:18 -05:00 committed by Steven Rostedt
parent 781d062482
commit d57c5d51a3
4 changed files with 39 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
arch/x86/Kconfig
View File

@ -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

7
arch/x86/include/asm/ftrace.h
View File

@ -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)
{

32
arch/x86/kernel/entry_64.S
View File

@ -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

6
arch/x86/kernel/x8664_ksyms_64.c
View File

@ -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);