Linux: fix a process name setting bug that doesn't currently affect us.

base/setproctitle_linux.c

 // Copyright (c) 2009 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file implements BSD-style setproctitle() for Linux.
 // It is written such that it can easily be compiled outside Chromium.
 //
 // The Linux kernel sets up two locations in memory to pass arguments and
 // environment variables to processes. First, there are two char* arrays stored
 // one after another: argv and environ. A pointer to argv is passed to main(),
@@ skipping 73 matching lines @@
       environ[i] = copy;
     }
   }
   // Put the title in argv[0]. We have to zero out the space first since the
   // kernel doesn't actually look for a null terminator unless we make the
   // argument list longer than it started.
   avail_size = page_end - (uintptr_t) g_main_argv[0];
   memset(g_main_argv[0], 0, avail_size);
   va_start(ap, fmt);
   if (fmt[0] == '-') {
-    vsnprintf(g_main_argv[0], avail_size, fmt, ap);
+    vsnprintf(g_main_argv[0], avail_size, &fmt[1], ap);
   } else {
     size_t size = snprintf(g_main_argv[0], avail_size, "%s ", g_orig_argv0);
     if (size < avail_size)
       vsnprintf(g_main_argv[0] + size, avail_size - size, fmt, ap);
   }
   va_end(ap);
   g_main_argv[1] = NULL;
 }
 
 // A version of this built into glibc would not need this function, since
 // it could stash the argv pointer in __libc_start_main(). But we need it.
 void setproctitle_init(char** main_argv) {
   uintptr_t page_size = sysconf(_SC_PAGESIZE);
   // Check that the argv array is in fact on the same page of memory
   // as the environment array just as an added measure of protection.
   if (((uintptr_t) environ) / page_size == ((uintptr_t) main_argv) / page_size)
     g_main_argv = main_argv;
 }