[PATCH] Use external tool for creating backtraces on crashes if available.

[Matthias Hopf]

Make the code for fork/exec-ing a helper program to perform a backtrace
more generic, so it can be used to call /usr/bin/xorg-backtrace, a
script which invokes gdb to create reasonable backtraces.
On errors it falls back to the generic method.

Based on a patch by Matthias Hopf mhopf at suse.de

Signed-off-by: Jon TURNEY <jon.turney at dronecode.org.uk>
---
 os/Makefile.am |    2 +-
 os/backtrace.c |   64 ++++++++++++++++++++++++++++++++++++++++++++++---------
 2 files changed, 54 insertions(+), 12 deletions(-)

diff --git a/os/Makefile.am b/os/Makefile.am
index 3e4f2c5..b40ee78 100644
--- a/os/Makefile.am
+++ b/os/Makefile.am
@@ -1,6 +1,6 @@
 noinst_LTLIBRARIES = libos.la liblog.la
 
-AM_CFLAGS = $(DIX_CFLAGS) $(SHA1_CFLAGS)
+AM_CFLAGS = $(DIX_CFLAGS) $(SHA1_CFLAGS) -DBINDIR=\"$(bindir)\"
 
 SECURERPC_SRCS = rpcauth.c
 XDMCP_SRCS = xdmcp.c
diff --git a/os/backtrace.c b/os/backtrace.c
index 7ca6dab..b1ad535 100644
--- a/os/backtrace.c
+++ b/os/backtrace.c
@@ -28,6 +28,13 @@
 #include "os.h"
 #include "misc.h"
 
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <errno.h>
+
 #ifdef HAVE_BACKTRACE
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE
@@ -41,6 +48,10 @@ void xorg_backtrace(void)
     const char *mod;
     int size, i;
     Dl_info info;
+
+    if (xorg_backtrace_gdb () == 0)
+	return;
+
     ErrorF("\nBacktrace:\n");
     size = backtrace(array, 64);
     for (i = 0; i < size; i++) {
@@ -121,8 +132,12 @@ static int xorg_backtrace_frame(uintptr_t pc, int signo, void *arg)
 }
 # endif /* HAVE_WALKCONTEXT */
 
-# ifdef HAVE_PSTACK
-static int xorg_backtrace_pstack(void) {
+/*
+  fork/exec a program to create a backtrace
+  Returns 0 if successful.
+*/
+static int xorg_backtrace_exec_wrapper(const char* path)
+{
     pid_t kidpid;
     int pipefd[2];
 
@@ -130,7 +145,7 @@ static int xorg_backtrace_pstack(void) {
 	return -1;
     }
 
-    kidpid = fork1();
+    kidpid = fork();
 
     if (kidpid == -1) {
 	/* ERROR */
@@ -142,11 +157,13 @@ static int xorg_backtrace_pstack(void) {
 	seteuid(0);
 	close(STDIN_FILENO);
 	close(STDOUT_FILENO);
+	close(STDERR_FILENO);
 	dup2(pipefd[1],STDOUT_FILENO);
-	closefrom(STDERR_FILENO);
+	dup2(pipefd[1],STDERR_FILENO);
+	close(pipefd[1]);
 
 	snprintf(parent, sizeof(parent), "%d", getppid());
-	execle("/usr/bin/pstack", "pstack", parent, NULL);
+	execle(path, path, parent, NULL, NULL);
 	exit(1);
     } else {
 	/* PARENT */
@@ -154,13 +171,15 @@ static int xorg_backtrace_pstack(void) {
 	int kidstat;
 	int bytesread;
 	int done = 0;
-	
+	int status = -1;
+
 	close(pipefd[1]);
 
 	while (!done) {
 	    bytesread = read(pipefd[0], btline, sizeof(btline) - 1);
 
 	    if (bytesread > 0) {
+		status++;
 		btline[bytesread] = 0;
 		ErrorF("%s", btline);
 	    }
@@ -170,18 +189,38 @@ static int xorg_backtrace_pstack(void) {
 	}
 	close(pipefd[0]);
 	waitpid(kidpid, &kidstat, 0);
-	if (kidstat != 0)
-	    return -1;
+        if (!(WIFEXITED (kidstat) && WEXITSTATUS (kidstat) == 0))
+          {
+            ErrorF ("%s failed with returncode %d\n", path, WEXITSTATUS (kidstat));
+            return -1;
+          }
+        if (status < 10) {
+          ErrorF ("%s only produced %d lines of output\n", path, status);
+          return -1;
+        }
     }
     return 0;
 }
-# endif /* HAVE_PSTACK */
 
+# ifdef HAVE_PSTACK
+static int xorg_backtrace_pstack(void)
+{
+  return xorg_backtrace_exec_wrapper("/usr/bin/pstack");
+}
+#endif
+
+static int xorg_backtrace_gdb(void)
+{
+  return xorg_backtrace_exec_wrapper(BINDIR "/xorg-backtrace");
+}
 
 # if defined(HAVE_PSTACK) || defined(HAVE_WALKCONTEXT)
 
 void xorg_backtrace(void) {
 
+    if (xorg_backtrace_gdb () == 0)
+	return;
+
     ErrorF("\nBacktrace:\n");
 
 #  ifdef HAVE_PSTACK
@@ -206,8 +245,11 @@ void xorg_backtrace(void) {
 
 # else
 
-/* Default fallback if we can't find any way to get a backtrace */
-void xorg_backtrace(void) { return; }
+/* Default fallback if we can't find any better way to get a backtrace */
+void xorg_backtrace(void) {
+  if (xorg_backtrace_gdb () == 0)
+    return;
+}
 
 # endif
 #endif
-- 
1.7.2.3


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