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ftrace: Add -mfentry to Makefile on function tracer 

Thanks to Andi Kleen, gcc 4.6.0 now supports -mfentry for x86
(and hopefully soon for other archs). What this does is to have
the function profiler start at the beginning of the function
instead of after the stack is set up. As plain -pg (mcount) is
called after the stack is set up, and in some cases can have issues
with the function graph tracer. It also requires frame pointers to
be enabled.

The -mfentry now calls __fentry__ at the beginning of the function.
This allows for compiling without frame pointers and even has the
ability to access parameters if needed.

If the architecture and the compiler both support -mfentry then
use that instead.

Link: http://lkml.kernel.org/r/20120807194059.392617243@goodmis.org

Acked-by: H. Peter Anvin <hpa@linux.intel.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Cc: Michal Marek <mmarek@suse.cz>
Cc: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt 2011-02-09 13:15:59 -05:00 committed by Steven Rostedt
parent 48bb5dc6cd
commit a2546fae01
2 changed files with 10 additions and 1 deletions
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6
Makefile
View File

@ -609,7 +609,11 @@ KBUILD_CFLAGS += $(call cc-option, -femit-struct-debug-baseonly)
endif
ifdef CONFIG_FUNCTION_TRACER
KBUILD_CFLAGS += -pg
ifdef CONFIG_HAVE_FENTRY
CC_USING_FENTRY := $(call cc-option, -mfentry -DCC_USING_FENTRY)
endif
KBUILD_CFLAGS += -pg $(CC_USING_FENTRY)
KBUILD_AFLAGS += $(CC_USING_FENTRY)
ifdef CONFIG_DYNAMIC_FTRACE
ifdef CONFIG_HAVE_C_RECORDMCOUNT
BUILD_C_RECORDMCOUNT := y

5
kernel/trace/Kconfig
View File

@ -49,6 +49,11 @@ config HAVE_SYSCALL_TRACEPOINTS
help
See Documentation/trace/ftrace-design.txt
config HAVE_FENTRY
bool
help
Arch supports the gcc options -pg with -mfentry
config HAVE_C_RECORDMCOUNT
bool
help