about:startup - open the correct file, error check the fopen, use try/catch to check for failure in the js

browser/base/content/aboutStartup.js

@@ -4,7 +4,11 @@ var Ci = Components.interfaces;
 let launched, startup, restored;
 
 let runtime = Cc["@mozilla.org/xre/runtime;1"].getService(Ci.nsIXULRuntime);
+
+try {
   displayTimestamp("launched", launched = runtime.launchTimestamp);
+} catch(x) { }
+
 displayTimestamp("started", startup = runtime.startupTimestamp);
 if (launched)
   displayDuration("started", startup - launched);

toolkit/xre/nsAppRunner.cpp

@@ -810,6 +810,7 @@ NS_IMETHODIMP nsXULAppInfo::GetLaunchTimestamp(PRUint64 *aTimestamp)
 {
 #ifdef XP_UNIX
   FILE *uptime;
+  long tickspersecond = sysconf(_SC_CLK_TCK);
   unsigned long long sec, ssec;
 
   uptime = fopen("/proc/uptime", "r");
@@ -819,9 +820,10 @@ NS_IMETHODIMP nsXULAppInfo::GetLaunchTimestamp(PRUint64 *aTimestamp)
 
   FILE *pidstat;
   pid_t pid = getpid();
-  char *statpath = PR_smprintf("/proc/%d/uptime", pid);
+  char *statpath = PR_smprintf("/proc/%d/stat", pid);
   pidstat = fopen(statpath, "r");
-  PR_smprintf_free(statpath);
+  if (!pidstat)
+    return NS_ERROR_FAILURE;
 
   char stat[512];
   memset(&stat, 0, 512);
@@ -829,6 +831,7 @@ NS_IMETHODIMP nsXULAppInfo::GetLaunchTimestamp(PRUint64 *aTimestamp)
   if (n <= 0)
     return NS_ERROR_FAILURE;
   fclose(pidstat);
+  PR_smprintf_free(statpath);
 
   PRTime starttime = 0;
   sscanf(strrchr(stat, ')') + 2,
@@ -836,8 +839,7 @@ NS_IMETHODIMP nsXULAppInfo::GetLaunchTimestamp(PRUint64 *aTimestamp)
          "%*u %*u %*u %*u %*u %*d %*d %*d %*d %llu",
          &starttime);
 
-  printf("%llu, %llu\n", boottime, starttime * PR_USEC_PER_SEC);
-  *aTimestamp = boottime + (starttime * PR_USEC_PER_SEC);
+  *aTimestamp = boottime + ((starttime / tickspersecond) * PR_USEC_PER_SEC);
   return NS_OK;
 #else
   return NS_ERROR_NOT_IMPLEMENTED;