Messages in this thread | | | Date | Wed, 09 Feb 2011 15:02:49 -0500 | From | Steven Rostedt <> | Subject | [RFC][PATCH 0/4] ftrace: Use -mfentry when supported (this is for x86_64 right now) |
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Thanks to Andi Kleen gcc 4.6.0 now supports -mfentry with the -pg option to place a call to __fentry__ at the very beginning of the function instead of after the fact.
The old way:
00000000000000c4 <atomic_long_add>: c4: 55 push %rbp c5: 48 89 e5 mov %rsp,%rbp c8: e8 00 00 00 00 callq cd <atomic_long_add+0x9> c9: R_X86_64_PC32 mcount-0x4 cd: f0 48 01 3e lock add %rdi,(%rsi) d1: c9 leaveq d2: c3 retq
The new way:
000000000000009e <atomic_long_add>: 9e: e8 00 00 00 00 callq a3 <atomic_long_add+0x5> 9f: R_X86_64_PC32 __fentry__-0x4 a3: 55 push %rbp a4: 48 89 e5 mov %rsp,%rbp a7: f0 48 01 3e lock add %rdi,(%rsi) ab: 5d pop %rbp ac: c3 retq
Note, with -mfentry, frame pointers is no longer required by the function tracer. But this patch series still requires FRAME_POINTER to be set, since I need to figure out a good way to enable FRAME_POINTER only if gcc doesn't support this. But that can come later.
With the new __fentry__, we could possible record the parameters of a function call. This may take some work, and perhaps be a little like kprobes. But it is doable.
This is still just RFC. I only wrote the code to support x86_64 even though gcc 4.6.0 also supports i386. I figured I would post this first to get peoples reactions before converting i386 too. Other archs can soon follow.
-- Steve
The following patches are in:
git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-trace.git
branch: rfc/tracing/fentry
Steven Rostedt (4): ftrace: Make recordmcount.c handle __fentry__ ftrace: Add -mfentry to Makefile on function tracer ftrace: Do not test frame pointers if -mfentry is used ftrace/x86: Add support for -mfentry to x86_64
---- Makefile | 6 +++++- arch/x86/Kconfig | 1 + arch/x86/include/asm/ftrace.h | 7 ++++++- arch/x86/kernel/entry_64.S | 17 ++++++++++++++++- arch/x86/kernel/x8664_ksyms_64.c | 6 +++++- kernel/trace/Kconfig | 5 +++++ kernel/trace/trace_functions_graph.c | 5 ++++- scripts/recordmcount.h | 4 +++- 8 files changed, 45 insertions(+), 6 deletions(-)
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