[PATCH v2 6/7] btrace: improve enable error messages

Markus Metzger
2018-01-26T14:14:41Z

Improve the error message when GDB fails to start recording branch trace.

This patch also removes a zero buffer size check for PT to align with BTS. The
buffer size can not be configured to be zero.

2018-01-26 Markus Metzger <markus.t.metzger@intel.com>

gdb/
* nat/linux-btrace.c (perf_event_pt_event_type): Improve error message.
Remove parameter and change return type. Update callers.
(linux_enable_bts, linux_enable_pt): Improve error message.
(linux_enable_pt): Remove zero buffer size check.
(linux_enable_btrace): Improve error messages. Remove NULL return
check.
---
gdb/nat/linux-btrace.c | 69 +++++++++++++++++++++-----------------------------
1 file changed, 29 insertions(+), 40 deletions(-)

diff --git a/gdb/nat/linux-btrace.c b/gdb/nat/linux-btrace.c
index 23ad778..4425539 100644
--- a/gdb/nat/linux-btrace.c
+++ b/gdb/nat/linux-btrace.c
@@ -448,7 +448,7 @@ linux_enable_bts (ptid_t ptid, const struct btrace_config_bts *conf)
errno = 0;
scoped_fd fd (syscall (SYS_perf_event_open, &bts->attr, pid, -1, -1, 0));
if (fd.get () < 0)
- return nullptr;
+ error (_("Failed to start recording: %s"), safe_strerror (errno));

/* Convert the requested size in bytes to pages (rounding up). */
pages = ((size_t) conf->size / PAGE_SIZE
@@ -484,6 +484,7 @@ linux_enable_bts (ptid_t ptid, const struct btrace_config_bts *conf)
if ((__u64) length != data_size + PAGE_SIZE)
continue;

+ errno = 0;
/* The number of pages we request needs to be a power of two. */
data.reset (nullptr, length, PROT_READ, MAP_SHARED, fd.get (), 0);
if (data.get () != MAP_FAILED)
@@ -491,7 +492,7 @@ linux_enable_bts (ptid_t ptid, const struct btrace_config_bts *conf)
}

if (pages == 0)
- return nullptr;
+ error (_("Failed to map trace buffer: %s."), safe_strerror (errno));

struct perf_event_mmap_page *header = (struct perf_event_mmap_page *)
data.get ();
@@ -509,7 +510,7 @@ linux_enable_bts (ptid_t ptid, const struct btrace_config_bts *conf)

/* Check for overflows. */
if ((__u64) size != data_size)
- return nullptr;
+ error (_("Failed to determine trace buffer size."));
}
#endif /* defined (PERF_ATTR_SIZE_VER5) */

@@ -528,21 +529,23 @@ linux_enable_bts (ptid_t ptid, const struct btrace_config_bts *conf)

#if defined (PERF_ATTR_SIZE_VER5)

-/* Determine the event type.
- Returns zero on success and fills in TYPE; returns -1 otherwise. */
+/* Determine the event type. */

static int
-perf_event_pt_event_type (int *type)
+perf_event_pt_event_type ()
{
- gdb_file_up file =
- gdb_fopen_cloexec ("/sys/bus/event_source/devices/intel_pt/type", "r");
+ const char *filename = "/sys/bus/event_source/devices/intel_pt/type";
+
+ errno = 0;
+ gdb_file_up file = gdb_fopen_cloexec (filename, "r");
if (file.get () == nullptr)
- return -1;
+ error (_("Failed to open %s: %s."), filename, safe_strerror (errno));

- int found = fscanf (file.get (), "%d", type);
- if (found == 1)
- return 0;
- return -1;
+ int type, found = fscanf (file.get (), "%d", &type);
+ if (found != 1)
+ error (_("Failed to read the PT event type from %s."), filename);
+
+ return type;
}

/* Enable branch tracing in Intel Processor Trace format. */
@@ -552,14 +555,7 @@ linux_enable_pt (ptid_t ptid, const struct btrace_config_pt *conf)
{
struct btrace_tinfo_pt *pt;
size_t pages;
- int pid, pg, errcode, type;
-
- if (conf->size == 0)
- return NULL;
-
- errcode = perf_event_pt_event_type (&type);
- if (errcode != 0)
- return NULL;
+ int pid, pg;

pid = ptid_get_lwp (ptid);
if (pid == 0)
@@ -573,7 +569,7 @@ linux_enable_pt (ptid_t ptid, const struct btrace_config_pt *conf)
pt = &tinfo->variant.pt;

pt->attr.size = sizeof (pt->attr);
- pt->attr.type = type;
+ pt->attr.type = perf_event_pt_event_type ();

pt->attr.exclude_kernel = 1;
pt->attr.exclude_hv = 1;
@@ -582,13 +578,13 @@ linux_enable_pt (ptid_t ptid, const struct btrace_config_pt *conf)
errno = 0;
scoped_fd fd (syscall (SYS_perf_event_open, &pt->attr, pid, -1, -1, 0));
if (fd.get () < 0)
- return nullptr;
+ error (_("Failed to start recording: %s"), safe_strerror (errno));

/* Allocate the configuration page. */
scoped_mmap data (nullptr, PAGE_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED,
fd.get (), 0);
if (data.get () == MAP_FAILED)
- return nullptr;
+ error (_("Failed to map trace user page: %s."), safe_strerror (errno));

struct perf_event_mmap_page *header = (struct perf_event_mmap_page *)
data.get ();
@@ -630,6 +626,7 @@ linux_enable_pt (ptid_t ptid, const struct btrace_config_pt *conf)

header->aux_size = data_size;

+ errno = 0;
aux.reset (nullptr, length, PROT_READ, MAP_SHARED, fd.get (),
header->aux_offset);
if (aux.get () != MAP_FAILED)
@@ -637,7 +634,7 @@ linux_enable_pt (ptid_t ptid, const struct btrace_config_pt *conf)
}

if (pages == 0)
- return nullptr;
+ error (_("Failed to map trace buffer: %s."), safe_strerror (errno));

pt->pt.size = aux.size ();
pt->pt.mem = (const uint8_t *) aux.release ();
@@ -656,8 +653,7 @@ linux_enable_pt (ptid_t ptid, const struct btrace_config_pt *conf)
static struct btrace_target_info *
linux_enable_pt (ptid_t ptid, const struct btrace_config_pt *conf)
{
- errno = EOPNOTSUPP;
- return NULL;
+ error (_("GDB does not support Intel PT."));
}

#endif /* !defined (PERF_ATTR_SIZE_VER5) */
@@ -667,27 +663,20 @@ linux_enable_pt (ptid_t ptid, const struct btrace_config_pt *conf)
struct btrace_target_info *
linux_enable_btrace (ptid_t ptid, const struct btrace_config *conf)
{
- struct btrace_target_info *tinfo;
-
- tinfo = NULL;
switch (conf->format)
{
case BTRACE_FORMAT_NONE:
- break;
+ error (_("Bad branch trace format."));
+
+ default:
+ error (_("Unknown branch trace format."));

case BTRACE_FORMAT_BTS:
- tinfo = linux_enable_bts (ptid, &conf->bts);
- break;
+ return linux_enable_bts (ptid, &conf->bts);

case BTRACE_FORMAT_PT:
- tinfo = linux_enable_pt (ptid, &conf->pt);
- break;
+ return linux_enable_pt (ptid, &conf->pt);
}
-
- if (tinfo == NULL)
- error (_("Unknown error."));
-
- return tinfo;
}

/* Disable BTS tracing. */
--
1.8.3.1