Date: Wed, 13 Feb 2008 11:25:55 +0100
From: Markus Metzger <markus.t.metzger@intel.com>
To: ak@suse.de, hpa@zytor.com, linux-kernel@vger.kernel.org, mingo@elte.hu,
       tglx@linutronix.de
Cc: markus.t.metzger@intel.com, markus.t.metzger@gmail.com,
       suresh.b.siddha@intel.com, roland@redhat.com, akpm@linux-foundation.org,
       mtk.manpages@gmail.com, eranian@googlemail.com
Subject: [patch 2/2] x86, ptrace, man: corresponding man pages
Message-ID: <20080213112555.A3640@sedona.ch.intel.com>
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Man pages describing the user API of the ptrace BTS extensions.

Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>
---

Index: man/man2/ptrace.2
===================================================================
--- man.orig/man2/ptrace.2	2008-02-13 09:35:47.%N +0100
+++ man/man2/ptrace.2	2008-02-13 09:41:31.%N +0100
@@ -40,6 +40,9 @@
 .\"        PTRACE_SETSIGINFO, PTRACE_SYSEMU, PTRACE_SYSEMU_SINGLESTEP
 .\"    (Thanks to Blaisorblade, Daniel Jacobowitz and others who helped.)
 .\"
+.\" Modified Feb 2008, Markus Metzger <markus.t.metzger@intel.com>
+.\"     Added PTRACE_BTS_* commands
+.\"
 .TH PTRACE 2 2007-11-15 "Linux" "Linux Programmer's Manual"
 .SH NAME
 ptrace \- process trace
@@ -378,6 +381,135 @@
 detached in this way regardless of which method was used to initiate
 tracing.
 (\fIaddr\fP is ignored.)
+.LP
+The following ptrace commands provide access to the hardware's last
+branch recording. They may not be available on all architectures.
+.LP
+Last branch recording stores an execution trace of the traced
+process. For every (conditional) control flow change, the source and
+destination address are stored. On some architectures, control flow
+changes inside the kernel are recorded, as well. On later
+architectures, these are automatically filtered out.
+.LP
+The buffer (called Branch Trace Store) can be configured to be either
+circular, or to send a signal to the traced task when it is about to
+overflow. Not all methods may be available on all architectures.
+.LP
+The buffer can be accessed in two ways matching the above
+configurations: either as an array of BTS records from newest
+record to older records, one record at a time; or all records at once,
+from oldest to newest.
+.LP
+The former is mostly used for circular buffers to capture a tail of
+the execution trace (e.g. for debugging); the latter is mostly used to
+collect a continuous trace (e.g. for profiling) where the user drains
+the hardware buffer into a larger private buffer or into a file.
+.LP
+In addition to branches, timestamps (in jiffies) may optionally be
+recorded when the traced process arrives and departs,
+respectively. This information can be used to obtain a qualitative
+execution order, if more than one process is traced.
+.LP
+A BTS record is defined as:
+.LP
+.nf
+enum ptrace_bts_qualifier {
+	PTRACE_BTS_INVALID = 0,
+	PTRACE_BTS_BRANCH,
+	PTRACE_BTS_TASK_ARRIVES,
+	PTRACE_BTS_TASK_DEPARTS
+};
+.sp
+struct ptrace_bts_record {
+	u64 qualifier;
+	union {
+		/* PTRACE_BTS_BRANCH */
+		struct {
+			u64 from_ip;
+			u64 to_ip;
+		} lbr;
+		/* PTRACE_BTS_TASK_ARRIVES or
+		   PTRACE_BTS_TASK_DEPARTS */
+		u64 timestamp;
+	} variant;
+};
+.fi
+.LP
+For configuring last branch recording and for querying its status, the
+following struct is used:
+.LP
+.nf
+struct ptrace_bts_config {
+	u32 size;
+	u32 flags;
+	u32 signal;
+	u32 bts_size;
+};
+.fi
+.LP
+\fISize\fP is either the requested or the actual size of the kernel
+BTS buffer in bytes.
+\fIFlags\fP is a bitmask of options, which are specified by the
+following flags:
+.RS
+.TP
+.BR PTRACE_BTS_O_TRACE
+Collect branch trace records.
+.TP
+.BR PTRACE_BTS_O_SCHED
+Collect scheduling timing information.
+.TP
+.BR PTRACE_BTS_O_SIGNAL
+Send \fIsignal\fP to the traced task in case of a buffer overflow. May
+only be used together with PTRACE_BTS_O_ALLOC for configuration purposes.
+.TP
+.BR PTRACE_BTS_O_ALLOC
+Allocate a BTS buffer of size \fIsize\fP. Frees any previously
+allocated buffer for the same task.
+.RE
+\fISignal\fP is the signal to send to the traced task in case of a
+buffer overflow.
+\fIBts_size\fP is the actual size of the \fIptrace_bts_record\fP
+structure in bytes. It is ignored for configuration purposes.
+.TP
+.BR PTRACE_BTS_CONFIG
+Configure last branch recording. \fIaddr\fP points to a
+\fIptrace_bts_config\fP structure (see above); \fIdata\fP specifies
+the size of that structure.
+Returns the number of bytes read.
+.TP
+.BR PTRACE_BTS_STATUS
+Writes the actual configuration into a \fIptrace_bts_config\fP
+structure pointed to by \fIaddr\fP. The caller is responsible for
+allocating memory at \fIaddr\fP to hold a \fIptrace_bts_config\fP
+structure. \fIData\fP specifies the size of that structure.
+Returns the number of bytes written.
+.TP
+.BR PTRACE_BTS_SIZE
+Returns the number of BTS records available for draining. For a
+circular buffer, this number is meaningless.
+(\fIaddr\fP and \fIdata\fP are ignored.)
+.TP
+.BR PTRACE_BTS_GET
+Reads a single BTS record at index \fIdata\fP into \fIaddr\fP. The
+caller is responsible for allocating memory at \fIaddr\fP to hold one
+\fIptrace_bts_record\fP structure.
+The bigger the index, the older the record; the latest record can
+always be found at index 0.
+Returns the number of bytes written.
+.TP
+.BR PTRACE_BTS_CLEAR
+Clears the BTS buffer. This command can be used after a manual
+draining using PTRACE_BTS_GET commands.
+(\fIaddr\fP and \fIdata\fP are ignored.)
+.TP
+.BR PTRACE_BTS_DRAIN
+Reads all available BTS records into the buffer pointed to by
+\fIaddr\fP and clears the buffer. Records are read from oldest to
+newest. Returns the number of BTS records drained. The caller
+is responsible for allocating enough memory to hold an array of
+PTRACE_BTS_SIZE \fIptrace_bts_record\fP structures. \fIData\fP
+specifies the size of that buffer.
 .SH "RETURN VALUE"
 On success,
 .B PTRACE_PEEK*
@@ -432,6 +564,16 @@
 .B ESRCH
 The specified process does not exist, or is not currently being traced
 by the caller, or is not stopped (for requests that require that).
+.TP
+.B EOPNOTSUPP
+The operation is not supported on this architecture.
+.TP
+.B ENOMEM
+Not enough memory to allocate the BTS buffer.
+.TP
+.B ENXIO
+An attempt to access BTS information has been made without allocating
+a BTS buffer first.
 .SH "CONFORMING TO"
 SVr4, 4.3BSD
 .SH NOTES
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