util: add the backtrace printing function as separate util

Might as well make this easier to re-use since it doesn't do anything
specific to litest.

Part-of: <https://gitlab.freedesktop.org/libinput/libinput/-/merge_requests/1066>

meson.build

@@ -255,6 +255,7 @@ endif
 # Basic compilation test to make sure the headers include and define all the
 # necessary bits.
 util_headers = [
+		'util-backtrace.h',
 		'util-bits.h',
 		'util-input-event.h',
 		'util-list.h',

src/util-backtrace.h

@@ -0,0 +1,79 @@
+/*
+ * Copyright © 2024 Red Hat, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+#include "config.h"
+
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/wait.h>
+
+static inline void
+backtrace_print(FILE *fp)
+{
+#if HAVE_GSTACK
+	pid_t parent, child;
+	int pipefd[2];
+
+	if (pipe(pipefd) == -1)
+		return;
+
+	parent = getpid();
+	child = fork();
+
+	if (child == 0) {
+		char pid[8];
+
+		close(pipefd[0]);
+		dup2(pipefd[1], STDOUT_FILENO);
+
+		sprintf(pid, "%d", parent);
+
+		execlp("gstack", "gstack", pid, NULL);
+		exit(errno);
+	}
+
+	/* parent */
+	char buf[1024];
+	int status, nread;
+
+	close(pipefd[1]);
+	waitpid(child, &status, 0);
+
+	status = WEXITSTATUS(status);
+	if (status != 0) {
+		fprintf(fp, "ERROR: gstack failed, no backtrace available: %s\n",
+			   strerror(status));
+	} else {
+		fprintf(fp, "\nBacktrace:\n");
+		while ((nread = read(pipefd[0], buf, sizeof(buf) - 1)) > 0) {
+			buf[nread] = '\0';
+			fprintf(stderr, "%s", buf);
+		}
+		fprintf(fp, "\n");
+	}
+	close(pipefd[0]);
+#endif
+}

test/litest.c

@@ -63,6 +63,8 @@
 #include "quirks.h"
 #include "builddir.h"
 
+#include "util-backtrace.h"
+
 #include <linux/kd.h>
 
 #define evbit(t, c) ((t) << 16U | (c & 0xffff))
@@ -151,53 +153,13 @@ _litest_checkpoint(const char *func,
 static void
 litest_backtrace(void)
 {
-#if HAVE_GSTACK
-	pid_t parent, child;
-	int pipefd[2];
-
+#ifndef LITEST_DISABLE_BACKTRACE_LOGGING
 	if (RUNNING_ON_VALGRIND) {
-		litest_log("  Using valgrind, omitting backtrace\n");
+		fprintf(stderr, "Using valgrind, omitting backtrace\n");
 		return;
 	}
 
-	if (pipe(pipefd) == -1)
-		return;
-
-	parent = getpid();
-	child = fork();
-
-	if (child == 0) {
-		char pid[8];
-
-		close(pipefd[0]);
-		dup2(pipefd[1], STDOUT_FILENO);
-
-		sprintf(pid, "%d", parent);
-
-		execlp("gstack", "gstack", pid, NULL);
-		exit(errno);
-	}
-
-	/* parent */
-	char buf[1024];
-	int status, nread;
-
-	close(pipefd[1]);
-	waitpid(child, &status, 0);
-
-	status = WEXITSTATUS(status);
-	if (status != 0) {
-		litest_log("ERROR: gstack failed, no backtrace available: %s\n",
-			   strerror(status));
-	} else {
-		litest_log("\nBacktrace:\n");
-		while ((nread = read(pipefd[0], buf, sizeof(buf) - 1)) > 0) {
-			buf[nread] = '\0';
-			litest_log("%s", buf);
-		}
-		litest_log("\n");
-	}
-	close(pipefd[0]);
+	backtrace_print(stderr);
 #endif
 }