[patch v3 08/16] linux, btrace: perf_event based branch tracing

[markus dot t dot metzger at intel dot com]

From: Markus Metzger <markus.t.metzger@intel.com>

Implement branch tracing on Linux based on perf_event such taht it can be shared
between gdb and gdbserver.

The actual btrace target ops will be implemented on top.

2012-08-14 Markus Metzger <markus.t.metzger@intel.com>

	* common/linux_btrace.h: New file.
	* common/linux_btrace.c: New file.
	* Makefile.in: Add linux-btrace rules.

gdbserver/
	* Makefile.in: Add linux-btrace rules.


---
 gdb/Makefile.in           |    6 +-
 gdb/common/linux-btrace.c |  382 +++++++++++++++++++++++++++++++++++++++++++++
 gdb/common/linux-btrace.h |   76 +++++++++
 gdb/gdbserver/Makefile.in |    6 +-
 4 files changed, 468 insertions(+), 2 deletions(-)
 create mode 100644 gdb/common/linux-btrace.c
 create mode 100644 gdb/common/linux-btrace.h

diff --git a/gdb/Makefile.in b/gdb/Makefile.in
index 7601d5b..f6df0e0 100644
--- a/gdb/Makefile.in
+++ b/gdb/Makefile.in
@@ -828,7 +828,7 @@ gnulib/import/extra/snippet/arg-nonnull.h gnulib/import/extra/snippet/c++defs.h
 gnulib/import/extra/snippet/warn-on-use.h \
 gnulib/import/stddef.in.h gnulib/import/inttypes.in.h inline-frame.h skip.h \
 common/common-utils.h common/xml-utils.h common/buffer.h common/ptid.h \
-common/format.h common/host-defs.h utils.h \
+common/format.h common/host-defs.h common/linux-btrace.h utils.h \
 common/linux-osdata.h gdb-dlfcn.h auto-load.h probe.h stap-probe.h gdb_bfd.h
 
 # Header files that already have srcdir in them, or which are in objdir.
@@ -1944,6 +1944,10 @@ vec.o: ${srcdir}/common/vec.c
 	$(COMPILE) $(srcdir)/common/vec.c
 	$(POSTCOMPILE)
 
+linux-btrace.o: ${srcdir}/common/linux-btrace.c
+	$(COMPILE) $(srcdir)/common/linux-btrace.c
+	$(POSTCOMPILE)
+
 #
 # gdb/tui/ dependencies
 #
diff --git a/gdb/common/linux-btrace.c b/gdb/common/linux-btrace.c
new file mode 100644
index 0000000..da858e1
--- /dev/null
+++ b/gdb/common/linux-btrace.c
@@ -0,0 +1,382 @@
+/* Linux-dependent part of branch trace support for GDB, and GDBserver.
+
+   Copyright (C) 2012 Free Software Foundation, Inc.
+
+   Contributed by Intel Corp. <markus.t.metzger@intel.com>
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+/* Needed for _ () used in gdb_assert ().  */
+#ifdef GDBSERVER
+#include "server.h"
+#else
+#include "defs.h"
+#endif
+
+#include "linux-btrace.h"
+#include "common-utils.h"
+#include "gdb_assert.h"
+
+#if HAVE_LINUX_PERF_EVENT_H
+
+#include <errno.h>
+#include <string.h>
+#include <stdint.h>
+#include <unistd.h>
+#include <sys/syscall.h>
+#include <sys/mman.h>
+#include <sys/user.h>
+
+#if defined(__GNUC__)
+#  define memory_barrier() asm volatile ("" : : : "memory")
+#else
+#  define memory_barrier() do {} while (0)
+#endif
+
+/* A branch trace record in perf_event.  */
+struct perf_event_bts
+{
+  uint64_t from;
+  uint64_t to;
+};
+
+/* A perf_event branch trace sample.  */
+struct perf_event_sample
+{
+  struct perf_event_header header;
+  struct perf_event_bts bts;
+};
+
+/* Get the perf_event header.  */
+static inline volatile struct perf_event_mmap_page *
+perf_event_header (struct btrace_target_info* tinfo)
+{
+  return tinfo->buffer;
+}
+
+/* Get the size of the perf_event mmap buffer.  */
+static inline size_t
+perf_event_mmap_size (const struct btrace_target_info *tinfo)
+{
+  /* The branch trace buffer is preceded by a configuration page.  */
+  return (tinfo->size + 1) * PAGE_SIZE;
+}
+
+/* Get the size of the perf_event buffer.  */
+static inline size_t
+perf_event_buffer_size (struct btrace_target_info* tinfo)
+{
+  return tinfo->size * PAGE_SIZE;
+}
+
+/* Get the start address of the perf_event buffer.  */
+static inline const uint8_t *
+perf_event_buffer_begin (struct btrace_target_info* tinfo)
+{
+  return ((const uint8_t *) tinfo->buffer) + PAGE_SIZE;
+}
+
+/* Get the end address of the perf_event buffer.  */
+static inline const uint8_t *
+perf_event_buffer_end (struct btrace_target_info* tinfo)
+{
+  return perf_event_buffer_begin (tinfo) + perf_event_buffer_size (tinfo);
+}
+
+/* Check whether an address is in the kernel.  */
+static inline int
+perf_event_is_kernel_addr (const struct btrace_target_info *tinfo,
+			   uint64_t addr)
+{
+  return tinfo->ptr_bits && (addr & ((uint64_t) 1 << (tinfo->ptr_bits - 1)));
+}
+
+/* Check whether a perf_event record should be skipped.  */
+static inline int
+perf_event_skip_record (const struct btrace_target_info *tinfo,
+			const struct perf_event_bts *bts)
+{
+  return perf_event_is_kernel_addr (tinfo, bts->from);
+}
+
+/* Check whether a perf_event sample record is OK.  */
+static inline int
+perf_event_sample_ok (const struct perf_event_sample *sample)
+{
+  if (sample->header.type != PERF_RECORD_SAMPLE)
+    return 0;
+
+  if (sample->header.size != sizeof (*sample))
+    return 0;
+
+  return 1;
+}
+
+/* Branch trace is collected in a circular buffer [begin; end) as pairs of from
+   and to addresses (plus some header).
+
+   Start points into that buffer at the next sample position.
+   We read the collected samples backwards from start.
+
+   While reading the samples, we convert the information into a list of blocks.
+   For two adjacent samples s1 and s2, we form a block b such that b.begin =
+   s1.to and b.end = s2.from.
+
+   In case the buffer overflows during sampling, samples may be split.  */
+
+static VEC (btrace_block_s) *
+perf_event_read_bts (struct btrace_target_info* tinfo, const uint8_t *begin,
+		     const uint8_t *end, const uint8_t *start)
+{
+  VEC (btrace_block_s) *btrace = NULL;
+  struct perf_event_sample sample;
+  int read = 0, size = (end - begin);
+  struct btrace_block block = { 0, 0 };
+
+  gdb_assert (begin <= start);
+  gdb_assert (start <= end);
+
+  /* The buffer may contain a partial record as its last entry (i.e. when the
+     buffer size is not a mulitple of the sample size).  */
+  read = sizeof (sample) - 1;
+
+  for (; read < size; read += sizeof (sample))
+    {
+      const struct perf_event_sample *psample;
+
+      /* Find the next perf_event sample.  */
+      start -= sizeof (sample);
+      if (begin <= start)
+	psample = (const struct perf_event_sample *) start;
+      else
+	{
+	  int missing = (begin - start);
+
+	  start = (end - missing);
+
+	  if (missing == sizeof (sample))
+	    psample = (const struct perf_event_sample *) start;
+	  else
+	    {
+	      uint8_t *stack = (uint8_t *) &sample;
+
+	      memcpy (stack, start, missing);
+	      memcpy (stack + missing, begin, sizeof (sample) - missing);
+
+	      psample = &sample;
+	    }
+	}
+
+      if (!perf_event_sample_ok (psample))
+	{
+	  warning (_("Branch trace may be incomplete."));
+	  break;
+	}
+
+      if (perf_event_skip_record (tinfo, &psample->bts))
+	continue;
+
+      /* We found a valid sample, so we can complete the current block.  */
+      block.begin = psample->bts.to;
+
+      VEC_safe_push (btrace_block_s, btrace, &block);
+
+      /* Start the next block.  */
+      block.end = psample->bts.from;
+    }
+
+  return btrace;
+}
+
+/* See linux-btrace.h.  */
+int
+linux_supports_btrace (void)
+{
+  return 1;
+}
+
+/* See linux-btrace.h.  */
+int
+linux_btrace_has_changed (struct btrace_target_info *tinfo)
+{
+  volatile struct perf_event_mmap_page *header = perf_event_header (tinfo);
+
+  if (!header)
+    return 0;
+
+  return header->data_head != tinfo->data_head;
+}
+
+/* See linux-btrace.h.  */
+struct btrace_target_info *
+linux_enable_btrace (ptid_t ptid)
+{
+  struct btrace_target_info *tinfo;
+  int pid;
+
+  tinfo = xzalloc (sizeof (*tinfo));
+  tinfo->attr.size = sizeof (tinfo->attr);
+
+  tinfo->attr.type = PERF_TYPE_HARDWARE;
+  tinfo->attr.config = PERF_COUNT_HW_BRANCH_INSTRUCTIONS;
+  tinfo->attr.sample_period = 1;
+
+  /* We sample from and to address.  */
+  tinfo->attr.sample_type = PERF_SAMPLE_IP | PERF_SAMPLE_ADDR;
+
+  tinfo->attr.exclude_kernel = 1;
+  tinfo->attr.exclude_hv = 1;
+  tinfo->attr.exclude_idle = 1;
+
+  tinfo->ptr_bits = 0;
+
+  pid = ptid_get_lwp (ptid);
+  if (!pid)
+    pid = ptid_get_pid (ptid);
+
+  errno = 0;
+  tinfo->file = syscall (SYS_perf_event_open, &(tinfo->attr), pid, -1, -1, 0);
+  if (tinfo->file < 0)
+    goto err;
+
+  /* We hard-code the trace buffer size.
+     At some later time, we should make this configurable.  */
+  tinfo->size = 1;
+  tinfo->buffer = mmap (NULL, perf_event_mmap_size (tinfo),
+			PROT_READ, MAP_SHARED, tinfo->file, 0);
+  if (tinfo->buffer == MAP_FAILED)
+    goto err_file;
+
+  return tinfo;
+
+err_file:
+  close (tinfo->file);
+
+err:
+  xfree (tinfo);
+  return NULL;
+}
+
+/* See linux-btrace.h.  */
+int
+linux_disable_btrace (struct btrace_target_info *tinfo)
+{
+  int errcode;
+
+  if (!tinfo)
+    return EINVAL;
+
+  errno = 0;
+  errcode = munmap (tinfo->buffer, perf_event_mmap_size (tinfo));
+  if (errcode)
+    return errno;
+
+  close (tinfo->file);
+  xfree (tinfo);
+
+  return 0;
+}
+
+/* See linux-btrace.h.  */
+VEC (btrace_block_s) *
+linux_read_btrace (struct btrace_target_info *tinfo)
+{
+  VEC (btrace_block_s) *btrace = NULL;
+  volatile struct perf_event_mmap_page *header;
+  const uint8_t *begin, *end, *start;
+  unsigned long data_head, retries = 5;
+  size_t buffer_size;
+
+  header = perf_event_header (tinfo);
+  if (!header)
+    return btrace;
+
+  buffer_size = perf_event_buffer_size (tinfo);
+
+  /* We may need to retry reading the trace.  See below.  */
+  while (retries--)
+    {
+      data_head = header->data_head;
+
+      /* Make sure the trace data is up-to-date.  */
+      memory_barrier ();
+
+      /* If there new trace, let's read it.  */
+      if (data_head != tinfo->data_head)
+	{
+	  /* Data_head keeps growing; the buffer itself is circular.  */
+	  begin = perf_event_buffer_begin (tinfo);
+	  start = begin + (data_head % buffer_size);
+
+	  if (data_head <= buffer_size)
+	    end = start;
+	  else
+	    end = perf_event_buffer_end (tinfo);
+
+	  btrace = perf_event_read_bts (tinfo, begin, end, start);
+	}
+
+      /* The stopping thread notifies its ptracer before it is scheduled out.
+	 On multi-core systems, the debugger might therefore run while the
+	 kernel might be writing the last branch trace records.
+
+	 Let's check whether the data head moved while we read the trace.  */
+      if (data_head == header->data_head)
+	break;
+    }
+
+  tinfo->data_head = data_head;
+
+  return btrace;
+}
+
+#else /* !HAVE_LINUX_PERF_EVENT_H */
+
+/* See linux-btrace.h.  */
+int
+linux_supports_btrace (void)
+{
+  return 0;
+}
+
+/* See linux-btrace.h.  */
+int
+linux_btrace_has_changed (struct btrace_target_info *tinfo)
+{
+  return 0;
+}
+
+/* See linux-btrace.h.  */
+struct btrace_target_info *
+linux_enable_btrace (ptid_t ptid)
+{
+  return NULL;
+}
+
+/* See linux-btrace.h.  */
+int
+linux_disable_btrace (struct btrace_target_info *tinfo)
+{
+  return ENOSYS;
+}
+
+/* See linux-btrace.h.  */
+VEC (btrace_block_s) *
+linux_read_btrace (struct btrace_target_info *tinfo)
+{
+}
+
+#endif /* !HAVE_LINUX_PERF_EVENT_H */
diff --git a/gdb/common/linux-btrace.h b/gdb/common/linux-btrace.h
new file mode 100644
index 0000000..b0f8459
--- /dev/null
+++ b/gdb/common/linux-btrace.h
@@ -0,0 +1,76 @@
+/* Linux-dependent part of branch trace support for GDB, and GDBserver.
+
+   Copyright (C) 2012 Free Software Foundation, Inc.
+
+   Contributed by Intel Corp. <markus.t.metzger@intel.com>
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#ifndef LINUX_BTRACE_H
+#define LINUX_BTRACE_H
+
+#include "btrace-common.h"
+#include "config.h"
+#include "vec.h"
+#include "ptid.h"
+#include <stddef.h>
+#include <stdint.h>
+
+#if HAVE_LINUX_PERF_EVENT_H
+#  include <linux/perf_event.h>
+#endif
+
+/* Branch trace target information per thread.  */
+struct btrace_target_info
+{
+#if HAVE_LINUX_PERF_EVENT_H
+  /* The Linux perf_event configuration for collecting the branch trace.  */
+  struct perf_event_attr attr;
+
+  /* The mmap configuration mapping the branch trace perf_event buffer.
+
+     file      .. the file descriptor
+     buffer    .. the mmapped memory buffer
+     size      .. the buffer's size in pages without the configuration page
+     data_head .. the data head from the last read  */
+  int file;
+  void *buffer;
+  size_t size;
+  unsigned long data_head;
+#endif /* HAVE_LINUX_PERF_EVENT_H */
+
+  /* The size of a pointer in bits for this thread.
+     The information is used to identify kernel addresses in order to skip
+     records from/to kernel space.  */
+  int ptr_bits;
+};
+
+/* Check whether branch tracing is supported.  */
+extern int linux_supports_btrace (void);
+
+/* Enable branch tracing for @ptid.  */
+extern struct btrace_target_info *linux_enable_btrace (ptid_t ptid);
+
+/* Disable branch tracing and deallocate @tinfo.  */
+extern int linux_disable_btrace (struct btrace_target_info *tinfo);
+
+/* Check whether there is new trace data available.  */
+extern int linux_btrace_has_changed (struct btrace_target_info *);
+
+/* Read branch trace data.  */
+extern VEC (btrace_block_s) *linux_read_btrace (struct btrace_target_info *);
+
+#endif /* LINUX_BTRACE_H */
diff --git a/gdb/gdbserver/Makefile.in b/gdb/gdbserver/Makefile.in
index ae5a60e..d571cd5 100644
--- a/gdb/gdbserver/Makefile.in
+++ b/gdb/gdbserver/Makefile.in
@@ -146,7 +146,7 @@ SFILES=	$(srcdir)/gdbreplay.c $(srcdir)/inferiors.c $(srcdir)/dll.c \
 	$(srcdir)/common/vec.c $(srcdir)/common/gdb_vecs.c \
 	$(srcdir)/common/common-utils.c $(srcdir)/common/xml-utils.c \
 	$(srcdir)/common/linux-osdata.c $(srcdir)/common/ptid.c \
-	$(srcdir)/common/buffer.c
+	$(srcdir)/common/buffer.c $(srcdir)/common/linux-btrace.c
 
 DEPFILES = @GDBSERVER_DEPFILES@
 
@@ -415,6 +415,7 @@ signals_h = $(srcdir)/../../include/gdb/signals.h $(signals_def)
 ptid_h = $(srcdir)/../common/ptid.h
 ax_h = $(srcdir)/ax.h
 agent_h = $(srcdir)/../common/agent.h
+linux_btrace_h = $(srcdir)/../common/linux-btrace.h
 linux_osdata_h = $(srcdir)/../common/linux-osdata.h
 vec_h = $(srcdir)/../common/vec.h
 gdb_vecs_h = $(srcdir)/../common/gdb_vecs.h
@@ -532,6 +533,9 @@ format.o: ../common/format.c $(server_h)
 agent.o: ../common/agent.c $(server_h) $(agent_h)
 	$(CC) -c $(CPPFLAGS) $(INTERNAL_CFLAGS) $<
 
+linux-btrace.o: ../common/linux-btrace.c $(linux_btrace_h) $(server_h)
+	$(CC) -c $(CPPFLAGS) $(INTERNAL_CFLAGS) $<
+
 # We build vasprintf with -DHAVE_CONFIG_H because we want that unit to
 # include our config.h file.  Otherwise, some system headers do not get
 # included, and the compiler emits a warning about implicitly defined
-- 
1.7.1