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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/[email protected] Acked-by: H. Peter Anvin <[email protected]> Acked-by: Ingo Molnar <[email protected]> Cc: Michal Marek <[email protected]> Cc: Andi Kleen <[email protected]> Signed-off-by: Steven Rostedt <[email protected]>
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