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[patch v4 20/24] btrace, gdbserver: read branch trace incrementally
- From: Markus Metzger <markus dot t dot metzger at intel dot com>
- To: jan dot kratochvil at redhat dot com
- Cc: gdb-patches at sourceware dot org, Pedro Alves <palves at redhat dot com>
- Date: Wed, 3 Jul 2013 11:14:30 +0200
- Subject: [patch v4 20/24] btrace, gdbserver: read branch trace incrementally
- References: <1372842874-28951-1-git-send-email-markus dot t dot metzger at intel dot com>
Read branch trace data incrementally and extend the current trace rather than
discarding it and reading the entire trace buffer each time.
If the branch trace buffer overflowed, we can't extend the current trace so we
discard it and start anew by reading the entire branch trace buffer.
Reviewed-by: Eli Zaretskii <eliz@gnu.org>
CC: Pedro Alves <palves@redhat.com>
2013-07-03 Markus Metzger <markus.t.metzger@intel.com>
* common/linux-btrace.c (perf_event_read_bts, linux_read_btrace):
Support delta reads.
* common/linux-btrace.h (linux_read_btrace): Change parameters
and return type to allow error reporting.
* common/btrace-common.h (btrace_read_type)<btrace_read_delta>:
New.
* btrace.c (btrace_compute_ftrace): Start from the end of
the current trace.
(btrace_stitch_trace, btrace_clear_history): New.
(btrace_fetch): Read delta trace.
(btrace_clear): Move clear history code to btrace_clear_history.
(parse_xml_btrace): Throw an error if parsing failed.
* target.h (struct target_ops)<to_read_btrace>: Change parameters
and return type to allow error reporting.
(target_read_btrace): Change parameters and return type to allow
error reporting.
* target.c (target_read_btrace): Update.
* remote.c (remote_read_btrace): Support delta reads. Pass
errors on.
gdbserver/
* target.h (target_ops)<read_btrace>: Change parameters and
return type to allow error reporting.
* server.c (handle_qxfer_btrace): Support delta reads. Pass
trace reading errors on.
* linux-low.c (linux_low_read_btrace): Pass trace reading
errors on.
---
gdb/NEWS | 4 +
gdb/btrace.c | 136 ++++++++++++++++++++++++++++++++++++++------
gdb/common/btrace-common.h | 6 ++-
gdb/common/linux-btrace.c | 84 +++++++++++++++++++--------
gdb/common/linux-btrace.h | 5 +-
gdb/doc/gdb.texinfo | 8 +++
gdb/gdbserver/linux-low.c | 18 +++++-
gdb/gdbserver/server.c | 11 +++-
gdb/gdbserver/target.h | 6 +-
gdb/remote.c | 23 ++++---
gdb/target.c | 9 ++-
gdb/target.h | 14 +++--
12 files changed, 254 insertions(+), 70 deletions(-)
diff --git a/gdb/NEWS b/gdb/NEWS
index 9b9de71..433a968 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -124,6 +124,10 @@ qXfer:libraries-svr4:read's annex
necessary for library list updating, resulting in significant
speedup.
+qXfer:btrace:read's annex
+ The qXfer:btrace:read packet supports a new annex 'delta' to read
+ branch trace incrementally.
+
* New features in the GDB remote stub, GDBserver
** GDBserver now supports target-assisted range stepping. Currently
diff --git a/gdb/btrace.c b/gdb/btrace.c
index 822926c..072e9d3 100644
--- a/gdb/btrace.c
+++ b/gdb/btrace.c
@@ -600,9 +600,9 @@ btrace_compute_ftrace (struct btrace_thread_info *btinfo,
DEBUG ("compute ftrace");
gdbarch = target_gdbarch ();
- begin = NULL;
- end = NULL;
- level = INT_MAX;
+ begin = btinfo->begin;
+ end = btinfo->end;
+ level = begin != NULL ? -btinfo->level : INT_MAX;
blk = VEC_length (btrace_block_s, btrace);
while (blk != 0)
@@ -718,27 +718,138 @@ btrace_teardown (struct thread_info *tp)
btrace_clear (tp);
}
+/* Adjust the block trace in order to stitch old and new trace together.
+ Return 0 on success; -1, otherwise. */
+
+static int
+btrace_stitch_trace (VEC (btrace_block_s) **btrace,
+ const struct btrace_thread_info *btinfo)
+{
+ struct btrace_function *end;
+ struct btrace_insn *insn;
+ btrace_block_s *block;
+
+ /* If we don't have trace, there's nothing to do. */
+ if (VEC_empty (btrace_block_s, *btrace))
+ return 0;
+
+ end = btinfo->end;
+ gdb_assert (end != NULL);
+
+ block = VEC_last (btrace_block_s, *btrace);
+ insn = VEC_last (btrace_insn_s, end->insn);
+
+ /* Check if we can extend the trace. */
+ if (block->end < insn->pc)
+ return -1;
+
+ /* If the current PC at the end of the block is the same as in our current
+ trace, there are two explanations:
+ 1. we executed the instruction and some branch brought us back.
+ 2. we have not made any progress.
+ In the first case, the delta trace vector should contain at least two
+ entries.
+ In the second case, the delta trace vector should contain exactly one
+ entry for the partial block containing the current PC. Remove it. */
+ if (block->end == insn->pc && VEC_length (btrace_block_s, *btrace) == 1)
+ {
+ VEC_pop (btrace_block_s, *btrace);
+ return 0;
+ }
+
+ DEBUG ("stitching %s to %s", ftrace_print_insn_addr (insn),
+ core_addr_to_string_nz (block->end));
+
+ /* We adjust the last block to start at the end of our current trace. */
+ gdb_assert (block->begin == 0);
+ block->begin = insn->pc;
+
+ /* We simply pop the last insn so we can insert it again as part of
+ the normal branch trace computation.
+ Since instruction iterators are based on indices in the instructions
+ vector, we don't leave any pointers dangling. */
+ DEBUG ("pruning insn at %s for stitching", ftrace_print_insn_addr (insn));
+
+ VEC_pop (btrace_insn_s, end->insn);
+
+ /* The instructions vector may become empty temporarily if this has
+ been the only instruction in this function segment.
+ This violates the invariant but will be remedied shortly. */
+ return 0;
+}
+
+/* Clear the branch trace histories in BTINFO. */
+
+static void
+btrace_clear_history (struct btrace_thread_info *btinfo)
+{
+ xfree (btinfo->insn_history);
+ xfree (btinfo->call_history);
+ xfree (btinfo->replay);
+
+ btinfo->insn_history = NULL;
+ btinfo->call_history = NULL;
+ btinfo->replay = NULL;
+}
+
/* See btrace.h. */
void
btrace_fetch (struct thread_info *tp)
{
struct btrace_thread_info *btinfo;
+ struct btrace_target_info *tinfo;
VEC (btrace_block_s) *btrace;
struct cleanup *cleanup;
+ int errcode;
DEBUG ("fetch thread %d (%s)", tp->num, target_pid_to_str (tp->ptid));
+ btrace = NULL;
btinfo = &tp->btrace;
- if (btinfo->target == NULL)
+ tinfo = btinfo->target;
+ if (tinfo == NULL)
return;
- btrace = target_read_btrace (btinfo->target, btrace_read_new);
cleanup = make_cleanup (VEC_cleanup (btrace_block_s), &btrace);
+ /* Let's first try to extend the trace we already have. */
+ if (btinfo->end != NULL)
+ {
+ errcode = target_read_btrace (&btrace, tinfo, btrace_read_delta);
+ if (errcode == 0)
+ {
+ /* Success. Let's try to stitch the traces together. */
+ errcode = btrace_stitch_trace (&btrace, btinfo);
+ }
+ else
+ {
+ /* We failed to read delta trace. Let's try to read new trace. */
+ errcode = target_read_btrace (&btrace, tinfo, btrace_read_new);
+
+ /* If we got any new trace, discard what we have. */
+ if (errcode == 0 && !VEC_empty (btrace_block_s, btrace))
+ btrace_clear (tp);
+ }
+
+ /* If we were not able to read the trace, we start over. */
+ if (errcode != 0)
+ {
+ btrace_clear (tp);
+ errcode = target_read_btrace (&btrace, tinfo, btrace_read_all);
+ }
+ }
+ else
+ errcode = target_read_btrace (&btrace, tinfo, btrace_read_all);
+
+ /* If we were not able to read the branch trace, signal an error. */
+ if (errcode != 0)
+ error ("Failed to read branch trace.");
+
+ /* Compute the trace, provided we have any. */
if (!VEC_empty (btrace_block_s, btrace))
{
- btrace_clear (tp);
+ btrace_clear_history (btinfo);
btrace_compute_ftrace (btinfo, btrace);
}
@@ -773,13 +884,7 @@ btrace_clear (struct thread_info *tp)
btinfo->begin = NULL;
btinfo->end = NULL;
- xfree (btinfo->insn_history);
- xfree (btinfo->call_history);
- xfree (btinfo->replay);
-
- btinfo->insn_history = NULL;
- btinfo->call_history = NULL;
- btinfo->replay = NULL;
+ btrace_clear_history (btinfo);
}
/* See btrace.h. */
@@ -871,10 +976,7 @@ parse_xml_btrace (const char *buffer)
errcode = gdb_xml_parse_quick (_("btrace"), "btrace.dtd", btrace_elements,
buffer, &btrace);
if (errcode != 0)
- {
- do_cleanups (cleanup);
- return NULL;
- }
+ error (_("Error parsing branch trace."));
/* Keep parse results. */
discard_cleanups (cleanup);
diff --git a/gdb/common/btrace-common.h b/gdb/common/btrace-common.h
index b157c7c..e863a65 100644
--- a/gdb/common/btrace-common.h
+++ b/gdb/common/btrace-common.h
@@ -67,7 +67,11 @@ enum btrace_read_type
btrace_read_all,
/* Send all available trace, if it changed. */
- btrace_read_new
+ btrace_read_new,
+
+ /* Send the trace since the last request. This will fail if the trace
+ buffer overflowed. */
+ btrace_read_delta
};
#endif /* BTRACE_COMMON_H */
diff --git a/gdb/common/linux-btrace.c b/gdb/common/linux-btrace.c
index b30a6ec..649b535 100644
--- a/gdb/common/linux-btrace.c
+++ b/gdb/common/linux-btrace.c
@@ -169,11 +169,11 @@ perf_event_sample_ok (const struct perf_event_sample *sample)
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)
+ const uint8_t *end, const uint8_t *start, size_t size)
{
VEC (btrace_block_s) *btrace = NULL;
struct perf_event_sample sample;
- size_t read = 0, size = (end - begin);
+ size_t read = 0;
struct btrace_block block = { 0, 0 };
struct regcache *regcache;
@@ -249,6 +249,12 @@ perf_event_read_bts (struct btrace_target_info* tinfo, const uint8_t *begin,
block.end = psample->bts.from;
}
+ /* Push the last block, as well. We don't know where it ends, but we
+ know where it starts. If we're reading delta trace, we can fill in the
+ start address later on. Otherwise, we will prune it. */
+ block.begin = 0;
+ VEC_safe_push (btrace_block_s, btrace, &block);
+
return btrace;
}
@@ -501,21 +507,24 @@ linux_btrace_has_changed (struct btrace_target_info *tinfo)
/* See linux-btrace.h. */
-VEC (btrace_block_s) *
-linux_read_btrace (struct btrace_target_info *tinfo,
+int
+linux_read_btrace (VEC (btrace_block_s) **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;
+ unsigned long data_head, data_tail, retries = 5;
+ size_t buffer_size, size;
+ /* For delta reads, we return at least the partial last block containing
+ the current PC. */
if (type == btrace_read_new && !linux_btrace_has_changed (tinfo))
- return NULL;
+ return 0;
header = perf_event_header (tinfo);
buffer_size = perf_event_buffer_size (tinfo);
+ data_tail = tinfo->data_head;
/* We may need to retry reading the trace. See below. */
while (retries--)
@@ -523,23 +532,45 @@ linux_read_btrace (struct btrace_target_info *tinfo,
data_head = header->data_head;
/* Delete any leftover trace from the previous iteration. */
- VEC_truncate (btrace_block_s, btrace, 0);
+ VEC_truncate (btrace_block_s, *btrace, 0);
- /* If there's new trace, let's read it. */
- if (data_head != tinfo->data_head)
+ if (type == btrace_read_delta)
{
- /* 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);
+ /* Determine the number of bytes to read and check for buffer
+ overflows. */
+
+ /* Check for data head overflows. We might be able to recover from
+ those but they are very unlikely and it's not really worth the
+ effort, I think. */
+ if (data_head < data_tail)
+ return -EOVERFLOW;
+
+ /* If the buffer is smaller than the trace delta, we overflowed. */
+ size = data_head - data_tail;
+ if (buffer_size < size)
+ return -EOVERFLOW;
+ }
+ else
+ {
+ /* Read the entire buffer. */
+ size = buffer_size;
- btrace = perf_event_read_bts (tinfo, begin, end, start);
+ /* Adjust the size if the buffer has not overflowed, yet. */
+ if (data_head < size)
+ size = 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, size);
+
/* 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.
@@ -551,7 +582,11 @@ linux_read_btrace (struct btrace_target_info *tinfo,
tinfo->data_head = data_head;
- return btrace;
+ /* Prune the incomplete last block if we're not doing a delta read. */
+ if (!VEC_empty (btrace_block_s, *btrace) && type != btrace_read_delta)
+ VEC_pop (btrace_block_s, *btrace);
+
+ return 0;
}
#else /* !HAVE_LINUX_PERF_EVENT_H */
@@ -582,11 +617,12 @@ linux_disable_btrace (struct btrace_target_info *tinfo)
/* See linux-btrace.h. */
-VEC (btrace_block_s) *
-linux_read_btrace (struct btrace_target_info *tinfo,
+int
+linux_read_btrace (VEC (btrace_block_s) **btrace,
+ struct btrace_target_info *tinfo,
enum btrace_read_type type)
{
- return NULL;
+ return ENOSYS;
}
#endif /* !HAVE_LINUX_PERF_EVENT_H */
diff --git a/gdb/common/linux-btrace.h b/gdb/common/linux-btrace.h
index d4e8402..82397b7 100644
--- a/gdb/common/linux-btrace.h
+++ b/gdb/common/linux-btrace.h
@@ -71,7 +71,8 @@ extern struct btrace_target_info *linux_enable_btrace (ptid_t ptid);
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);
+extern int linux_read_btrace (VEC (btrace_block_s) **,
+ struct btrace_target_info *,
+ enum btrace_read_type);
#endif /* LINUX_BTRACE_H */
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index eb4896f..2dc45bc 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -39161,6 +39161,14 @@ Returns all available branch trace.
@item new
Returns all available branch trace if the branch trace changed since
the last read request.
+
+@item delta
+Returns the new branch trace since the last read request. Adds a new
+block to the end of the trace that begins at zero and ends at the source
+location of the first branch in the trace buffer. This extra block is
+used to stitch traces together.
+
+If the trace buffer overflowed, returns an error indicating the overflow.
@end table
This packet is not probed by default; the remote stub must request it
diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index 47ea76d..709405c 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -5964,15 +5964,25 @@ linux_low_enable_btrace (ptid_t ptid)
/* Read branch trace data as btrace xml document. */
-static void
+static int
linux_low_read_btrace (struct btrace_target_info *tinfo, struct buffer *buffer,
int type)
{
VEC (btrace_block_s) *btrace;
struct btrace_block *block;
- int i;
+ int i, errcode;
+
+ btrace = NULL;
+ errcode = linux_read_btrace (&btrace, tinfo, type);
+ if (errcode != 0)
+ {
+ if (errcode == -EOVERFLOW)
+ buffer_grow_str (buffer, "E.Overflow.");
+ else
+ buffer_grow_str (buffer, "E.Generic Error.");
- btrace = linux_read_btrace (tinfo, type);
+ return -1;
+ }
buffer_grow_str (buffer, "<!DOCTYPE btrace SYSTEM \"btrace.dtd\">\n");
buffer_grow_str (buffer, "<btrace version=\"1.0\">\n");
@@ -5984,6 +5994,8 @@ linux_low_read_btrace (struct btrace_target_info *tinfo, struct buffer *buffer,
buffer_grow_str (buffer, "</btrace>\n");
VEC_free (btrace_block_s, btrace);
+
+ return 0;
}
#endif /* HAVE_LINUX_BTRACE */
diff --git a/gdb/gdbserver/server.c b/gdb/gdbserver/server.c
index a172c98..c518f62 100644
--- a/gdb/gdbserver/server.c
+++ b/gdb/gdbserver/server.c
@@ -1343,7 +1343,7 @@ handle_qxfer_btrace (const char *annex,
{
static struct buffer cache;
struct thread_info *thread;
- int type;
+ int type, result;
if (the_target->read_btrace == NULL || writebuf != NULL)
return -2;
@@ -1375,6 +1375,8 @@ handle_qxfer_btrace (const char *annex,
type = btrace_read_all;
else if (strcmp (annex, "new") == 0)
type = btrace_read_new;
+ else if (strcmp (annex, "delta") == 0)
+ type = btrace_read_delta;
else
{
strcpy (own_buf, "E.Bad annex.");
@@ -1385,7 +1387,12 @@ handle_qxfer_btrace (const char *annex,
{
buffer_free (&cache);
- target_read_btrace (thread->btrace, &cache, type);
+ result = target_read_btrace (thread->btrace, &cache, type);
+ if (result != 0)
+ {
+ memcpy (own_buf, cache.buffer, cache.used_size);
+ return -3;
+ }
}
else if (offset > cache.used_size)
{
diff --git a/gdb/gdbserver/target.h b/gdb/gdbserver/target.h
index c57cb40..1bb1f23 100644
--- a/gdb/gdbserver/target.h
+++ b/gdb/gdbserver/target.h
@@ -420,8 +420,10 @@ struct target_ops
int (*disable_btrace) (struct btrace_target_info *tinfo);
/* Read branch trace data into buffer. We use an int to specify the type
- to break a cyclic dependency. */
- void (*read_btrace) (struct btrace_target_info *, struct buffer *, int type);
+ to break a cyclic dependency.
+ Return 0 on success; print an error message into BUFFER and return -1,
+ otherwise. */
+ int (*read_btrace) (struct btrace_target_info *, struct buffer *, int type);
/* Return true if target supports range stepping. */
int (*supports_range_stepping) (void);
diff --git a/gdb/remote.c b/gdb/remote.c
index b352ca6..705aa66 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -11417,13 +11417,14 @@ remote_teardown_btrace (struct btrace_target_info *tinfo)
/* Read the branch trace. */
-static VEC (btrace_block_s) *
-remote_read_btrace (struct btrace_target_info *tinfo,
+static int
+remote_read_btrace (VEC (btrace_block_s) **btrace,
+ struct btrace_target_info *tinfo,
enum btrace_read_type type)
{
struct packet_config *packet = &remote_protocol_packets[PACKET_qXfer_btrace];
struct remote_state *rs = get_remote_state ();
- VEC (btrace_block_s) *btrace = NULL;
+ struct cleanup *cleanup;
const char *annex;
char *xml;
@@ -11442,6 +11443,9 @@ remote_read_btrace (struct btrace_target_info *tinfo,
case btrace_read_new:
annex = "new";
break;
+ case btrace_read_delta:
+ annex = "delta";
+ break;
default:
internal_error (__FILE__, __LINE__,
_("Bad branch tracing read type: %u."),
@@ -11450,15 +11454,14 @@ remote_read_btrace (struct btrace_target_info *tinfo,
xml = target_read_stralloc (¤t_target,
TARGET_OBJECT_BTRACE, annex);
- if (xml != NULL)
- {
- struct cleanup *cleanup = make_cleanup (xfree, xml);
+ if (xml == NULL)
+ return -1;
- btrace = parse_xml_btrace (xml);
- do_cleanups (cleanup);
- }
+ cleanup = make_cleanup (xfree, xml);
+ *btrace = parse_xml_btrace (xml);
+ do_cleanups (cleanup);
- return btrace;
+ return 0;
}
static int
diff --git a/gdb/target.c b/gdb/target.c
index 58388f3..33f774e 100644
--- a/gdb/target.c
+++ b/gdb/target.c
@@ -4237,18 +4237,19 @@ target_teardown_btrace (struct btrace_target_info *btinfo)
/* See target.h. */
-VEC (btrace_block_s) *
-target_read_btrace (struct btrace_target_info *btinfo,
+int
+target_read_btrace (VEC (btrace_block_s) **btrace,
+ struct btrace_target_info *btinfo,
enum btrace_read_type type)
{
struct target_ops *t;
for (t = current_target.beneath; t != NULL; t = t->beneath)
if (t->to_read_btrace != NULL)
- return t->to_read_btrace (btinfo, type);
+ return t->to_read_btrace (btrace, btinfo, type);
tcomplain ();
- return NULL;
+ return ENOSYS;
}
/* See target.h. */
diff --git a/gdb/target.h b/gdb/target.h
index 632bf1d..4a20533 100644
--- a/gdb/target.h
+++ b/gdb/target.h
@@ -882,9 +882,12 @@ struct target_ops
be attempting to talk to a remote target. */
void (*to_teardown_btrace) (struct btrace_target_info *tinfo);
- /* Read branch trace data. */
- VEC (btrace_block_s) *(*to_read_btrace) (struct btrace_target_info *,
- enum btrace_read_type);
+ /* Read branch trace data into DATA. The vector is cleared before any
+ new data is added.
+ Returns 0 on success; a negative error code, otherwise. */
+ int (*to_read_btrace) (VEC (btrace_block_s) **data,
+ struct btrace_target_info *,
+ enum btrace_read_type);
/* Stop trace recording. */
void (*to_stop_recording) (void);
@@ -2010,8 +2013,9 @@ extern void target_disable_btrace (struct btrace_target_info *btinfo);
extern void target_teardown_btrace (struct btrace_target_info *btinfo);
/* See to_read_btrace in struct target_ops. */
-extern VEC (btrace_block_s) *target_read_btrace (struct btrace_target_info *,
- enum btrace_read_type);
+extern int target_read_btrace (VEC (btrace_block_s) **,
+ struct btrace_target_info *,
+ enum btrace_read_type);
/* See to_stop_recording in struct target_ops. */
extern void target_stop_recording (void);
--
1.7.1