os: Use an external tool for creating backtraces on crash, if available.

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.

v2: disable backtrace code on MinGW

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

Signed-off-by: Jon TURNEY <jon.turney@dronecode.org.uk>
Reviewed-by: Yaakov Selkowitz <yselkowitz@users.sourceforge.net>

2 files changed, 46 insertions, 10 deletions

diff --git a/os/Makefile.am b/os/Makefile.am
index a1bbb4d1e..0b0eb79d1 100644
--- a/os/Makefile.am
+++ b/os/Makefile.am
@@ -1,6 +1,6 @@
 noinst_LTLIBRARIES = libos.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 3d1195b86..3100d1a13 100644
--- a/os/backtrace.c
+++ b/os/backtrace.c
@@ -222,10 +222,25 @@ xorg_backtrace_frame(uintptr_t pc, int signo, void *arg)
 }
 #endif                          /* HAVE_WALKCONTEXT */
 
-#ifdef HAVE_PSTACK
+#include <sys/types.h>
+#if !defined(__WIN32__) || defined(__CYGWIN__)
+#include <sys/wait.h>
+#endif
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+/*
+  fork/exec a program to create a backtrace
+  Returns 0 if successful.
+*/
 static int
-xorg_backtrace_pstack(void)
+xorg_backtrace_exec_wrapper(const char *path)
 {
+#if defined(WIN32) && !defined(__CYGWIN__)
+    ErrorFSigSafe("Backtrace not implemented on Windows");
+    return -1;
+#else
     pid_t kidpid;
     int pipefd[2];
 
@@ -233,7 +248,7 @@ xorg_backtrace_pstack(void)
         return -1;
     }
 
-    kidpid = fork1();
+    kidpid = fork();
 
     if (kidpid == -1) {
         /* ERROR */
@@ -246,11 +261,13 @@ 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 {
@@ -269,17 +286,35 @@ xorg_backtrace_pstack(void)
                 btline[bytesread] = 0;
                 ErrorFSigSafe("%s", btline);
             }
-            else if ((bytesread < 0) || ((errno != EINTR) && (errno != EAGAIN)))
+            else if ((bytesread == 0) ||
+                     ((errno != EINTR) && (errno != EAGAIN)))
                 done = 1;
         }
         close(pipefd[0]);
         waitpid(kidpid, &kidstat, 0);
-        if (kidstat != 0)
+        if (!(WIFEXITED(kidstat) && WEXITSTATUS(kidstat) == 0)) {
+            ErrorFSigSafe("%s failed with returncode %d\n", path,
+                          WEXITSTATUS(kidstat));
             return -1;
+        }
     }
     return 0;
+#endif
+}
+
+#ifdef HAVE_PSTACK
+static int
+xorg_backtrace_pstack(void)
+{
+    return xorg_backtrace_exec_wrapper("/usr/bin/pstack");
+}
+#endif
+
+static int
+xorg_backtrace_script(void)
+{
+    return xorg_backtrace_exec_wrapper(BINDIR "/xorg-backtrace");
 }
-#endif                          /* HAVE_PSTACK */
 
 #if defined(HAVE_PSTACK) || defined(HAVE_WALKCONTEXT)
 
@@ -316,7 +351,8 @@ xorg_backtrace(void)
 void
 xorg_backtrace(void)
 {
-    return;
+    if (xorg_backtrace_script() == 0)
+        return;
 }
 
 #endif