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 Acked-by: Ingo Molnar Cc: Michal Marek Cc: Andi Kleen Signed-off-by: Steven Rostedt --- Makefile | 6 +++++- kernel/trace/Kconfig | 5 +++++ 2 files changed, 10 insertions(+), 1 deletion(-) diff --git a/Makefile b/Makefile index ddf5be9..e7ca93f 100644 --- a/Makefile +++ b/Makefile @@ -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 diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig index 8c4c070..9301a0e 100644 --- a/kernel/trace/Kconfig +++ b/kernel/trace/Kconfig @@ -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 -- 1.7.10.4