Implement branch tracing on Linux based on perf_event such that it can be shared

between gdb and gdbserver.

gdb/
	* common/linux_btrace.h: New file.
	* common/linux_btrace.c: New file.
	* Makefile.in (SFILES): Add btrace.c.
	(HFILES_NO_SRCDIR): Add common/linux-btrace.h.
	(COMMON_OBS): Add btrace.o.
	(linux-btrace.o): New rule.

gdbserver/
	* Makefile.in (SFILES): Add $(srcdir)/common/linux-btrace.c.
	(linux_btrace_h): New variable.
	(linux-btrace.o): New rule.

2 files changed, 502 insertions, 0 deletions

diff --git a/gdb/common/linux-btrace.c b/gdb/common/linux-btrace.c
new file mode 100644
index 0000000..2f8c1cf
--- /dev/null
+++ b/gdb/common/linux-btrace.c
@@ -0,0 +1,425 @@
+/* Linux-dependent part of branch trace support for GDB, and GDBserver.
+
+   Copyright (C) 2013 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/>.  */
+
+#ifdef GDBSERVER
+#include "server.h"
+#else
+#include "defs.h"
+#endif
+
+#include "linux-btrace.h"
+#include "common-utils.h"
+#include "gdb_assert.h"
+#include "regcache.h"
+#include "gdbthread.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>
+
+/* A branch trace record in perf_event.  */
+struct perf_event_bts
+{
+  /* The linear address of the branch source.  */
+  uint64_t from;
+
+  /* The linear address of the branch destination.  */
+  uint64_t to;
+};
+
+/* A perf_event branch trace sample.  */
+struct perf_event_sample
+{
+  /* The perf_event sample header.  */
+  struct perf_event_header header;
+
+  /* The perf_event branch tracing payload.  */
+  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)
+{
+  uint64_t mask;
+
+  /* If we don't know the size of a pointer, we can't check.  Let's assume it's
+     not a kernel address in this case.  */
+  if (tinfo->ptr_bits == 0)
+    return 0;
+
+  /* A bit mask for the most significant bit in an address.  */
+  mask = (uint64_t) 1 << (tinfo->ptr_bits - 1);
+
+  /* Check whether the most significant bit in the address is set.  */
+  return (addr & mask) != 0;
+}
+
+/* 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)
+{
+  /* The hardware may report branches from kernel into user space.  Branches
+     from user into kernel space will be suppressed.  We filter the former to
+     provide a consistent branch trace excluding kernel.  */
+  return perf_event_is_kernel_addr (tinfo, bts->from);
+}
+
+/* Perform a few consistency checks on a perf event sample record.  This is
+   meant to catch cases when we get out of sync with the perf event stream.  */
+
+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 a 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, one sample may have its lower
+   part at the end and its upper part at the beginning of the buffer.  */
+
+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;
+  size_t read = 0, size = (end - begin);
+  struct btrace_block block = { 0, 0 };
+  struct regcache *regcache;
+
+  gdb_assert (begin <= start);
+  gdb_assert (start <= end);
+
+  /* The first block ends at the current pc.  */
+#ifdef GDBSERVER
+  regcache = get_thread_regcache (find_thread_ptid (tinfo->ptid), 1);
+#else
+  regcache = get_thread_regcache (tinfo->ptid);
+#endif
+  block.end = regcache_read_pc (regcache);
+
+  /* The buffer may contain a partial record as its last entry (i.e. when the
+     buffer size is not a multiple 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 in a backwards traversal.  */
+      start -= sizeof (sample);
+
+      /* If we're still inside the buffer, we're done.  */
+      if (begin <= start)
+	psample = (const struct perf_event_sample *) start;
+      else
+	{
+	  int missing;
+
+	  /* We're to the left of the ring buffer, we will wrap around and
+	     reappear at the very right of the ring buffer.  */
+
+	  missing = (begin - start);
+	  start = (end - missing);
+
+	  /* If the entire sample is missing, we're done.  */
+	  if (missing == sizeof (sample))
+	    psample = (const struct perf_event_sample *) start;
+	  else
+	    {
+	      uint8_t *stack;
+
+	      /* The sample wrapped around.  The lower part is at the end and
+		 the upper part is at the beginning of the buffer.  */
+	      stack = (uint8_t *) &sample;
+
+	      /* Copy the two parts so we have a contiguous 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.  */
+
+struct btrace_target_info *
+linux_enable_btrace (ptid_t ptid)
+{
+  struct btrace_target_info *tinfo;
+  int pid;
+
+  tinfo = xzalloc (sizeof (*tinfo));
+  tinfo->ptid = ptid;
+
+  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 == 0)
+    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;
+
+  errno = 0;
+  errcode = munmap (tinfo->buffer, perf_event_mmap_size (tinfo));
+  if (errcode != 0)
+    return errno;
+
+  close (tinfo->file);
+  xfree (tinfo);
+
+  return 0;
+}
+
+/* Check whether the branch trace has changed.  */
+
+static int
+linux_btrace_has_changed (struct btrace_target_info *tinfo)
+{
+  volatile struct perf_event_mmap_page *header = perf_event_header (tinfo);
+
+  return header->data_head != tinfo->data_head;
+}
+
+/* See linux-btrace.h.  */
+
+VEC (btrace_block_s) *
+linux_read_btrace (struct btrace_target_info *tinfo,
+		   enum btrace_read_type type)
+{
+  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;
+
+  if (type == btrace_read_new && !linux_btrace_has_changed (tinfo))
+    return NULL;
+
+  header = perf_event_header (tinfo);
+  buffer_size = perf_event_buffer_size (tinfo);
+
+  /* We may need to retry reading the trace.  See below.  */
+  while (retries--)
+    {
+      data_head = header->data_head;
+
+      /* If there's 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.  */
+
+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,
+		   enum btrace_read_type type)
+{
+  return NULL;
+}
+
+#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..d4e8402
--- /dev/null
+++ b/gdb/common/linux-btrace.h
@@ -0,0 +1,77 @@
+/* Linux-dependent part of branch trace support for GDB, and GDBserver.
+
+   Copyright (C) 2013 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 ptid of this thread.  */
+  ptid_t ptid;
+
+  /* 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);
+
+/* Read branch trace data.  */
+extern VEC (btrace_block_s) *linux_read_btrace (struct btrace_target_info *,
+						enum btrace_read_type);
+
+#endif /* LINUX_BTRACE_H */