bug#18680: [PATCH] Check if argv[0] is NULL in scm_boot_guile to avoid segfault

[Nala Ginrut]

This patch is for master branch, but the bug also appears in the
current stable-2.0 I think.

With the recent patch from Eli Zaretskii, there'd be one more step for argv[0]:
scm_i_mirror_backslashes (argv[0]);

But this cause my program segfault, since I have such line:
scm_boot_guile(0, {NULL}, &guilemain, NULL);

According to C11, it's allowed[1].
argv[argc] should be NULL.
If the value of argc is greater than zero, the string pointed to by argv[0]
represents the program name. But if argc is zero, argv[0] will be NULL, so
we have to check it first to avoid segfault.

Attached patch fixed this.

[1] http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf

From b6938156fe1ca2ba8a7db167604618eea31282f1 Mon Sep 17 00:00:00 2001
From: Nala Ginrut <nalagin...@gmail.com>
Date: Fri, 10 Oct 2014 23:54:24 +0800
Subject: [PATCH] Check argv[0] if it's NULL in scm_boot_guile

According to C11, argv[argc] should be NULL.
If the value of argc is greater than zero, the string pointed to by argv[0]
represents the program name. But if argc is zero, argv[0] will be NULL, so
we have to check it first to avoid segfault.

* libguile/init.c
---
 libguile/init.c |   10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/libguile/init.c b/libguile/init.c
index d2928bd..e11115c 100644
--- a/libguile/init.c
+++ b/libguile/init.c
@@ -311,8 +311,14 @@ scm_boot_guile (int argc, char ** argv, void (*main_func) (), void *closure)
   struct main_func_closure c;
 
   /* On Windows, convert backslashes in argv[0] to forward
-     slashes.  */
-  scm_i_mirror_backslashes (argv[0]);
+     slashes.
+     According to C11, argv[argc] should be NULL.
+     If the value of argc is greater than zero, the string pointed to by argv[0]
+     represents the program name. But if argc is zero, argv[0] will be NULL, so
+     we have to check it first to avoid segfault.
+   */
+  if (argc)
+    scm_i_mirror_backslashes (argv[0]);
   c.main_func = main_func;
   c.closure = closure;
   c.argc = argc;
-- 
1.7.10.4