make exec keep its argument list more reliably

Bits of exec code were putting the constructed commands into globals
PL_Argv and PL_Cmd, which could then be clobbered by reentrancy.
These are only global in order to manage their freeing, but that's
better managed by using the scope stack.  So replace them with automatic
variables, with ENTER/SAVEFREEPV/LEAVE to free the memory.  Also copy
the strings acquired from SVs, to avoid magic clobbering the buffers of
SVs already read.  Fixes [perl #129888].

1 files changed, 18 insertions, 10 deletions

diff --git a/cygwin/cygwin.c b/cygwin/cygwin.c
index a234825eba..fae90af000 100644
--- a/cygwin/cygwin.c
+++ b/cygwin/cygwin.c
@@ -90,11 +90,13 @@ int
 do_spawn (char *cmd)
 {
     dTHX;
-    char const **a;
+    char const **argv, **a;
     char *s;
     char const *metachars = "$&*(){}[]'\";\\?>|<~`\n";
     const char *command[4];
+    int result;
 
+    ENTER;
     while (*cmd && isSPACE(*cmd))
 	cmd++;
 
@@ -127,13 +129,16 @@ do_spawn (char *cmd)
 	    command[2] = cmd;
 	    command[3] = NULL;
 
-	    return do_spawnvp("sh",command);
+	    result = do_spawnvp("sh",command);
+	    goto leave;
 	}
 
-    Newx (PL_Argv, (s-cmd)/2+2, const char*);
-    PL_Cmd=savepvn (cmd,s-cmd);
-    a=PL_Argv;
-    for (s=PL_Cmd; *s;) {
+    Newx (argv, (s-cmd)/2+2, const char*);
+    SAVEFREEPV(argv);
+    cmd=savepvn (cmd,s-cmd);
+    SAVEFREEPV(cmd);
+    a=argv;
+    for (s=cmd; *s;) {
 	while (*s && isSPACE (*s)) s++;
 	if (*s)
 	    *(a++)=s;
@@ -142,10 +147,13 @@ do_spawn (char *cmd)
 	    *s++='\0';
     }
     *a = (char*)NULL;
-    if (!PL_Argv[0])
-        return -1;
-
-    return do_spawnvp(PL_Argv[0],(const char * const *)PL_Argv);
+    if (!argv[0])
+        result = -1;
+    else
+	result = do_spawnvp(argv[0],(const char * const *)argv);
+leave:
+    LEAVE;
+    return result;
 }
 
 #if (CYGWIN_VERSION_API_MINOR >= 181)