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[PATCH 08/16] linux, btrace: perf_event based branch tracing
- From: markus dot t dot metzger at intel dot com
- To: kettenis at gnu dot org
- Cc: gdb-patches at sourceware dot org, markus dot t dot metzger at gmail dot com, Markus Metzger <markus dot t dot metzger at intel dot com>
- Date: Wed, 23 May 2012 13:22:23 +0200
- Subject: [PATCH 08/16] linux, btrace: perf_event based branch tracing
- References: <1337772151-20265-1-git-send-email-markus.t.metzger@intel.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.
2012-05-23 Markus Metzger <markus.t.metzger@intel.com>
gdb/common/
* linux_btrace.h: New file
* linux_btrace.c: New file
gdb/
* Makefile.in: Add linux-btrace rules
gdb/gdbserver/
* Makefile.in: Add linux-btrace rules
---
gdb/Makefile.in | 7 +-
gdb/common/linux-btrace.c | 368 +++++++++++++++++++++++++++++++++++++++++++++
gdb/common/linux-btrace.h | 76 +++++++++
gdb/gdbserver/Makefile.in | 6 +-
4 files changed, 455 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 5fa7c12..b3fdd4f 100644
--- a/gdb/Makefile.in
+++ b/gdb/Makefile.in
@@ -826,7 +826,8 @@ 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/linux-osdata.h gdb-dlfcn.h auto-load.h probe.h stap-probe.h
+common/linux-osdata.h gdb-dlfcn.h auto-load.h probe.h stap-probe.h \
+common/linux-btrace.h
# Header files that already have srcdir in them, or which are in objdir.
@@ -1930,6 +1931,10 @@ 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..76bca75
--- /dev/null
+++ b/gdb/common/linux-btrace.c
@@ -0,0 +1,368 @@
+/* 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/>. */
+
+#include "linux-btrace.h"
+#include "common-utils.h"
+#include <errno.h>
+
+#if HAVE_LINUX_PERF_EVENT_H
+
+#include <string.h>
+#include <unistd.h>
+#include <sys/syscall.h>
+#include <sys/mman.h>
+#include <sys/user.h>
+
+typedef unsigned char byte;
+
+/* A branch trace record in perf_event. */
+struct perf_event_bts
+{
+ unsigned long long from;
+ unsigned long long to;
+};
+
+/* A perf_event branch trace sample. */
+struct perf_event_sample
+{
+ struct perf_event_header header;
+ struct perf_event_bts bts;
+};
+
+static inline volatile struct perf_event_mmap_page *
+perf_event_header (struct btrace_target_info* tinfo)
+{
+ return tinfo->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);
+}
+
+static inline size_t
+perf_event_buffer_size (struct btrace_target_info* tinfo)
+{
+ return (tinfo->size * PAGE_SIZE);
+}
+
+static inline const byte *
+perf_event_buffer_begin (struct btrace_target_info* tinfo)
+{
+ return ((const byte *) tinfo->buffer) + PAGE_SIZE;
+}
+
+static inline const byte *
+perf_event_buffer_end (struct btrace_target_info* tinfo)
+{
+ return perf_event_buffer_begin (tinfo) + perf_event_buffer_size (tinfo);
+}
+
+static inline int
+perf_event_skip_record (struct btrace_target_info* tinfo,
+ const struct perf_event_bts *bts)
+{
+ if (tinfo->ptr_bits)
+ {
+ int shift = tinfo->ptr_bits - 1;
+
+ /* Branch trace records branches from kernel space to user space. */
+ if (bts->from & (1ull << shift))
+ return 1;
+
+ /* Branch trace records branches from user space to kernel space. */
+ if (bts->to & (1ull << shift))
+ return 1;
+ }
+
+ return 0;
+}
+
+static inline int
+perf_event_check_sample (const struct perf_event_sample *sample)
+{
+ if (sample->header.type != PERF_RECORD_SAMPLE)
+ return EINVAL;
+
+ if (sample->header.size != sizeof (*sample))
+ return EINVAL;
+
+ return 0;
+}
+
+/* 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 int
+perf_event_read_bts (struct btrace_target_info* tinfo,
+ const byte *begin, const byte *end, const byte *start,
+ int (*fun) (struct linux_btrace_block *, void *),
+ void *arg)
+{
+ struct perf_event_sample sample;
+ int read = 0, size = (end - begin), errcode = 0;
+ struct linux_btrace_block block = { 0, 0 };
+
+ if (start < begin)
+ return EINVAL;
+
+ if (end < start)
+ return EINVAL;
+
+ /* 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
+ {
+ byte *stack = (byte *) &sample;
+
+ memcpy (stack, start, missing);
+ memcpy (stack + missing, begin, sizeof (sample) - missing);
+
+ psample = &sample;
+ }
+ }
+
+ errcode = perf_event_check_sample (psample);
+ if (errcode)
+ 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;
+
+ errcode = (*fun) (&block, arg);
+ if (errcode)
+ break;
+
+ /* Start the next block. */
+ block.end = psample->bts.from;
+ }
+
+ return errcode;
+}
+
+int
+linux_supports_btrace (void)
+{
+ return 1;
+}
+
+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);
+}
+
+struct btrace_target_info *
+linux_enable_btrace (ptid_t ptid)
+{
+ struct btrace_target_info *tinfo;
+ int pid;
+
+ tinfo = xzalloc (sizeof (*tinfo));
+ if (!tinfo)
+ {
+ errno = ENOMEM;
+ return NULL;
+ }
+
+ 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);
+
+ 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;
+}
+
+int
+linux_disable_btrace (struct btrace_target_info *tinfo)
+{
+ int errcode;
+
+ if (!tinfo)
+ return -EINVAL;
+
+ errcode = munmap (tinfo->buffer, perf_event_mmap_size (tinfo));
+ if (errcode)
+ return errno;
+
+ close (tinfo->file);
+ xfree (tinfo);
+
+ return 0;
+}
+
+int
+linux_read_btrace (struct btrace_target_info *tinfo,
+ int (*fun) (struct linux_btrace_block *, void *),
+ void *arg)
+{
+ volatile struct perf_event_mmap_page *header;
+ const byte *begin, *end, *start;
+ unsigned long data_head, retries = 5;
+ size_t buffer_size;
+ int errcode = 0;
+
+ if (!tinfo)
+ return EINVAL;
+
+ header = perf_event_header (tinfo);
+ if (!header)
+ return ENOSYS;
+
+ 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 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);
+
+ errcode = perf_event_read_bts (tinfo, begin, end, start, fun, arg);
+ }
+
+ /* 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 errcode;
+}
+
+#else /* HAVE_LINUX_PERF_EVENT_H */
+
+int
+linux_supports_btrace (void)
+{
+ return 0;
+}
+
+int
+linux_btrace_has_changed (struct btrace_target_info *tinfo)
+{
+ return 0;
+}
+
+struct btrace_target_info *
+linux_enable_btrace (ptid_t ptid)
+{
+ errno = ENOSYS;
+ return NULL;
+}
+
+int
+linux_disable_btrace (struct btrace_target_info *tinfo)
+{
+ return ENOSYS;
+}
+
+int
+linux_read_btrace (struct btrace_target_info *tinfo,
+ int (*fun) (struct linux_btrace_block *, void *),
+ void *arg)
+{
+ return ENOSYS;
+}
+
+#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..22f435a
--- /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 "config.h"
+#include "ptid.h"
+#include <stddef.h>
+
+#if HAVE_LINUX_PERF_EVENT_H
+# include <linux/perf_event.h>
+#endif
+
+/* A branch trace block on linux.
+ GDB and GDBserver don't agree on the definition of CORE_ADDR. In order to
+ allow sharing the perf_event access code, we stick to unsigned long long;
+ that's also what perf_event delivers. */
+struct linux_btrace_block
+{
+ unsigned long long begin;
+ unsigned long long end;
+};
+
+/* 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;
+};
+
+extern int linux_supports_btrace (void);
+extern struct btrace_target_info *linux_enable_btrace (ptid_t);
+extern int linux_disable_btrace (struct btrace_target_info *);
+extern int linux_btrace_has_changed (struct btrace_target_info *);
+extern int linux_read_btrace (struct btrace_target_info *,
+ int (*) (struct linux_btrace_block *, void *),
+ void *);
+
+#endif /* LINUX_BTRACE_H */
diff --git a/gdb/gdbserver/Makefile.in b/gdb/gdbserver/Makefile.in
index 50786d5..1f256de 100644
--- a/gdb/gdbserver/Makefile.in
+++ b/gdb/gdbserver/Makefile.in
@@ -139,7 +139,7 @@ SFILES= $(srcdir)/gdbreplay.c $(srcdir)/inferiors.c $(srcdir)/dll.c \
$(srcdir)/common/vec.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@
@@ -408,6 +408,7 @@ 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
# Since everything must include server.h, we make that depend on
@@ -514,6 +515,9 @@ buffer.o: ../common/buffer.c $(server_h)
agent.o: ../common/agent.c $(server_h) $(agent_h)
$(CC) -c $(CPPFLAGS) $(INTERNAL_CFLAGS) $< -DGDBSERVER
+linux-btrace.o: ../common/linux-btrace.c $(linux_btrace_h) $(server_h)
+ $(CC) -c $(CPPFLAGS) $(INTERNAL_CFLAGS) $< -DGDBSERVER
+
# 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