Messages in this thread | | | Date | Fri, 30 Nov 2007 16:56:52 +0100 | From | "Markus Metzger" <> | Subject | [patch 0/2] x86, ptrace: support for branch trace store(BTS) |
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Support for Intel's last branch recording to ptrace. This gives debuggers access to this hardware feature and allows them to show an execution trace of the debugged application.
Last branch recording (see section 18.5 in the Intel 64 and IA-32 Architectures Software Developer's Manual) allows taking an execution trace of the running application without instrumentation. When a branch is executed, the hardware logs the source and destination address in a cyclic buffer given to it by the OS.
This can be a great debugging aid. It shows you how exactly you got where you currently are without requiring you to do lots of single stepping and rerunning.
This patch manages the various buffers, configures the trace hardware, disentangles the trace, and provides a user interface via ptrace. On the high-level design: - there is one optional trace buffer per thread_struct - upon a context switch, the trace hardware is reconfigured to either disable tracing or to use the appropriate buffer for the new task. - tracing induces ~20% overhead as branch records are sent out on the bus. - the hardware collects trace per processor. To disentangle the traces for different tasks, we use separate buffers and reconfigure the trace hardware. - the low-level data layout is configured at cpu initialization time - different processors use different branch record formats
Opens: - kernel interface
patch 1/2 contains the kernel changes patch 2/2 contains changes to the ptrace man pages
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