[v2,7/7] btrace: check perf_event_paranoid
Commit Message
One recurring error on Debian systems is that the default perf_event_paranoid
setting disables the perf_event interface for user-space.
Check the current level and point the user to the file.
2018-01-26 Markus Metzger <markus.t.metzger@intel.com>
gdb/
* nat/linux-btrace.c (diagnose_perf_event_open_fail): New.
(linux_enable_pt, linux_enable_bts): Call
diagnose_perf_event_open_fail.
---
gdb/nat/linux-btrace.c | 32 ++++++++++++++++++++++++++++++--
1 file changed, 30 insertions(+), 2 deletions(-)
@@ -409,6 +409,34 @@ cpu_supports_bts (void)
}
}
+/* The perf_event_open syscall failed. Try to print a helpful error
+ message. */
+
+static void
+diagnose_perf_event_open_fail ()
+{
+ switch (errno)
+ {
+ case EPERM:
+ case EACCES:
+ {
+ const char *filename = "/proc/sys/kernel/perf_event_paranoid";
+ gdb_file_up file = gdb_fopen_cloexec (filename, "r");
+ if (file.get () == nullptr)
+ break;
+
+ int level, found = fscanf (file.get (), "%d", &level);
+ if (found == 1 && level > 2)
+ error (_("You do not have permission to record the process. "
+ "Try setting %s to 2 or less."), filename);
+ }
+
+ break;
+ }
+
+ error (_("Failed to start recording: %s"), safe_strerror (errno));
+}
+
/* Enable branch tracing in BTS format. */
static struct btrace_target_info *
@@ -448,7 +476,7 @@ 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)
- error (_("Failed to start recording: %s"), safe_strerror (errno));
+ diagnose_perf_event_open_fail ();
/* Convert the requested size in bytes to pages (rounding up). */
pages = ((size_t) conf->size / PAGE_SIZE
@@ -578,7 +606,7 @@ 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)
- error (_("Failed to start recording: %s"), safe_strerror (errno));
+ diagnose_perf_event_open_fail ();
/* Allocate the configuration page. */
scoped_mmap data (nullptr, PAGE_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED,