[igt-dev] [PATCH i-g-t] lib/igt_core: Detect gdb harder

* [igt-dev] [PATCH i-g-t] lib/igt_core: Detect gdb harder
@ 2020-01-22 16:43 Ville Syrjala
  2020-01-22 17:09 ` Chris Wilson
                   ` (3 more replies)
  0 siblings, 4 replies; 7+ messages in thread
From: Ville Syrjala @ 2020-01-22 16:43 UTC (permalink / raw)
  To: igt-dev

From: Ville Syrjälä <ville.syrjala@linux.intel.com>

The current gdb detection only works for the parent igt process,
but none of its children will see the gdb and so won't trap properly
in igt_fail_assert(). Also we will not detect gdb if it was attached
after the fact. Fix all of that by looking for the "TracerPid"
information in /proc/<pid>/status. We'll leave the current "assume
parent may be gdb" approach as a fallback.

Also annoyingly by default gdb will only track a single process.
To make it track all of them, and let them all run simultanously
one needs the following incantations:
 set detach-on-fork off
 set schedule-multiple on

Maybe that will save someone from having to trawl as many
docs/gogole hits as I did.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
---
 lib/igt_core.c | 38 ++++++++++++++++++++++++++++++++++++--
 1 file changed, 36 insertions(+), 2 deletions(-)

diff --git a/lib/igt_core.c b/lib/igt_core.c
index 0a0068946a6a..109b5926eac4 100644
--- a/lib/igt_core.c
+++ b/lib/igt_core.c
@@ -1609,12 +1609,12 @@ void igt_describe_f(const char *fmt, ...)
 	assert(ret < sizeof(__current_description));
 }
 
-static bool running_under_gdb(void)
+static bool is_gdb(pid_t pid)
 {
 	char pathname[30], buf[1024];
 	ssize_t len;
 
-	sprintf(pathname, "/proc/%d/exe", getppid());
+	sprintf(pathname, "/proc/%d/exe", pid);
 	len = readlink(pathname, buf, sizeof(buf) - 1);
 	if (len < 0)
 		return false;
@@ -1624,6 +1624,40 @@ static bool running_under_gdb(void)
 	return strncmp(basename(buf), "gdb", 3) == 0;
 }
 
+static pid_t tracer_pid(void)
+{
+	char pathname[30];
+	pid_t pid = 0;
+	FILE *f;
+
+	sprintf(pathname, "/proc/%d/status", getpid());
+
+	f = fopen(pathname, "r");
+	if (!f)
+		return getppid();
+
+	for (;;) {
+		char buf[1024];
+		char *s;
+
+		s = fgets(buf, sizeof(buf), f);
+		if (!s)
+			break;
+
+		if (sscanf(s, "TracerPid: %d", &pid) == 1)
+			break;
+	}
+
+	fclose(f);
+
+	return pid ?: getppid();
+}
+
+static bool running_under_gdb(void)
+{
+	return is_gdb(tracer_pid());
+}
+
 static void __write_stderr(const char *str, size_t len)
 {
 	igt_ignore_warn(write(STDERR_FILENO, str, len));
-- 
2.24.1

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