[PATCH] exec compatibility

[Phil Pennock <zsh-workers+phil.pennock@xxxxxxxxxxxx>]

I saw two options for cleaning the env:

 (1) *environ = NULL;
     in zexecve, make setting $_ conditional upon there being any
     environmental variables at all
 (2) pass a new envp around, which if NULL is new environ.

The second is more intrusive but doesn't have an ugly hack and it does
let _exactly_ the environment specified be passed.  I decided that "env"
could easily be a shell builtin if an explicit envp is passed, so
decided in favour of intrusiveness against hackiness.

I think that env-as-builtin is best left pending BINF-handler functions.
So this just leaves the way open.

I know that using a static data-segment variable for an envp is normally
not the best of ideas, I'm relying upon nothing messing with the explict
non-current newenvp before an execve().

-Phil

diff -ur zsh-head/Doc/Zsh/builtins.yo zsh-exec/Doc/Zsh/builtins.yo
--- zsh-head/Doc/Zsh/builtins.yo	Fri Mar 23 10:14:05 2007
+++ zsh-exec/Doc/Zsh/builtins.yo	Sun Apr 29 21:17:32 2007
@@ -375,7 +375,24 @@
 Read the arguments as input to the shell and execute the resulting
 command in the current shell process.
 )
-prefix(exec)
+findex(exec)
+item(tt(exec) [ tt(-cl) ] [ tt(-a) var(argv0) ] var(simple command))(
+The simple command argument is run in place of the current process,
+rather than as a sub-process.  The shell does not fork and is replaced.
+The shell does not invoke tT(TRAPEXIT), nor does it source tt(zlogout)
+files.
+The options are provided for compatibility with other shells.
+The tt(-c) flag clears the environment.
+The tt(-l) flag is equivalent to the tt(-) precommand modifier, to
+treat the replacement command as a login shell; the command is executed
+with a tt(-) prepended to its argv[0] string.  This flag has no effect
+if used together with the tt(-a) option.
+The tt(-a) option is used to explicitly specify the argv[0] string to be
+used by the replacement command and is directly equivalent to putting
+the tt($ARGV0) variable into the environment.
+
+See also noderef(Precommand Modifiers).
+)
 findex(exit)
 item(tt(exit) [ var(n) ])(
 Exit the shell with the exit status specified by var(n); if none
diff -ur zsh-head/Src/exec.c zsh-exec/Src/exec.c
--- zsh-head/Src/exec.c	Wed Feb 14 00:21:58 2007
+++ zsh-exec/Src/exec.c	Mon Apr 30 17:08:57 2007
@@ -144,6 +144,7 @@
 
 static int doneps4;
 static char *STTYval;
+static char *blank_env[] = { NULL };
 
 /* Execution functions. */
 
@@ -361,7 +362,7 @@
 
 /**/
 static int
-zexecve(char *pth, char **argv)
+zexecve(char *pth, char **argv, char **newenvp)
 {
     int eno;
     static char buf[PATH_MAX * 2];
@@ -379,7 +380,10 @@
 	sprintf(buf + 2, "%s/%s", pwd, pth);
     zputenv(buf);
     closedumps();
-    execve(pth, argv, environ);
+
+    if (newenvp == NULL)
+	    newenvp = environ;
+    execve(pth, argv, newenvp);
 
     /* If the execve returns (which in general shouldn't happen),   *
      * then check for an errno equal to ENOEXEC.  This errno is set *
@@ -414,14 +418,14 @@
 			    *ptr = '\0';
 			    argv[-2] = ptr2;
 			    argv[-1] = ptr + 1;
-			    execve(ptr2, argv - 2, environ);
+			    execve(ptr2, argv - 2, newenvp);
 			} else {
 			    argv[-1] = ptr2;
-			    execve(ptr2, argv - 1, environ);
+			    execve(ptr2, argv - 1, newenvp);
 			}
 		    } else if (eno == ENOEXEC) {
 			argv[-1] = "sh";
-			execve("/bin/sh", argv - 1, environ);
+			execve("/bin/sh", argv - 1, newenvp);
 		    }
 		} else if (eno == ENOEXEC) {
 		    for (t0 = 0; t0 != ct; t0++)
@@ -429,7 +433,7 @@
 			    break;
 		    if (t0 == ct) {
 			argv[-1] = "sh";
-			execve("/bin/sh", argv - 1, environ);
+			execve("/bin/sh", argv - 1, newenvp);
 		    }
 		}
 	    } else
@@ -467,13 +471,13 @@
 /* execute an external command */
 
 /**/
-void
-execute(LinkList args, int dash, int defpath)
+static void
+execute(LinkList args, int flags, int defpath)
 {
     Cmdnam cn;
     char buf[MAXCMDLEN], buf2[MAXCMDLEN];
     char *s, *z, *arg0;
-    char **argv, **pp;
+    char **argv, **pp, **newenvp = NULL;
     int eno = 0, ee;
 
     arg0 = (char *) peekfirst(args);
@@ -502,7 +506,7 @@
     if (unset(RESTRICTED) && (z = zgetenv("ARGV0"))) {
 	setdata(firstnode(args), (void *) ztrdup(z));
 	delenvvalue(z - 6);
-    } else if (dash) {
+    } else if (flags & BINF_DASH) {
     /* Else if the pre-command `-' was given, we add `-' *
      * to the front of argv[0] for this command.         */
 	sprintf(buf2, "-%s", arg0);
@@ -510,6 +514,9 @@
     }
 
     argv = makecline(args);
+    if (flags & BINF_CLEARENV)
+	newenvp = blank_env;
+
     /*
      * Note that we don't close fd's attached to process substitution
      * here, which should be visible to external processes.
@@ -522,7 +529,7 @@
     }
     for (s = arg0; *s; s++)
 	if (*s == '/') {
-	    int lerrno = zexecve(arg0, argv);
+	    int lerrno = zexecve(arg0, argv, newenvp);
 	    if (arg0 == s || unset(PATHDIRS) ||
 		(arg0[0] == '.' && (arg0 + 1 == s ||
 				    (arg0[1] == '.' && arg0 + 2 == s)))) {
@@ -559,7 +566,7 @@
 	    _exit(127);
 	}
 
-	ee = zexecve(pbuf, argv);
+	ee = zexecve(pbuf, argv, newenvp);
 
 	if ((dptr = strrchr(pbuf, '/')))
 	    *dptr = '\0';
@@ -576,7 +583,7 @@
 	    else {
 		for (pp = path; pp < cn->u.name; pp++)
 		    if (!**pp || (**pp == '.' && (*pp)[1] == '\0')) {
-			ee = zexecve(arg0, argv);
+			ee = zexecve(arg0, argv, newenvp);
 			if (isgooderr(ee, *pp))
 			    eno = ee;
 		    } else if (**pp != '/') {
@@ -584,7 +591,7 @@
 			strucpy(&z, *pp);
 			*z++ = '/';
 			strcpy(z, arg0);
-			ee = zexecve(buf, argv);
+			ee = zexecve(buf, argv, newenvp);
 			if (isgooderr(ee, *pp))
 			    eno = ee;
 		    }
@@ -592,7 +599,7 @@
 		strcat(nn, "/");
 		strcat(nn, cn->node.nam);
 	    }
-	    ee = zexecve(nn, argv);
+	    ee = zexecve(nn, argv, newenvp);
 
 	    if ((dptr = strrchr(nn, '/')))
 		*dptr = '\0';
@@ -601,7 +608,7 @@
 	}
 	for (pp = path; *pp; pp++)
 	    if (!(*pp)[0] || ((*pp)[0] == '.' && !(*pp)[1])) {
-		ee = zexecve(arg0, argv);
+		ee = zexecve(arg0, argv, newenvp);
 		if (isgooderr(ee, *pp))
 		    eno = ee;
 	    } else {
@@ -609,7 +616,7 @@
 		strucpy(&z, *pp);
 		*z++ = '/';
 		strcpy(z, arg0);
-		ee = zexecve(buf, argv);
+		ee = zexecve(buf, argv, newenvp);
 		if (isgooderr(ee, *pp))
 		    eno = ee;
 	    }
@@ -2026,6 +2033,49 @@
 		if (!strcmp(next, "--"))
 		     uremnode(args, firstnode(args));   
 	    }
+	    if (cflags & BINF_EXEC && nextnode(firstnode(args))) {
+		/* check for compatibility options to exec builtin */
+		char *next = (char *) getdata(nextnode(firstnode(args)));
+		char *cmdopt, *exec_argv0 = NULL;
+		while (next && *next == '-' && strlen(next) >= 2) {
+		    uremnode(args, firstnode(args));
+		    if (!strcmp(next, "--"))
+			break;
+		    for (cmdopt = &next[1]; *cmdopt; ++cmdopt) {
+			switch (*cmdopt) {
+			case 'a':
+			    exec_argv0 = (char *) getdata(nextnode(firstnode(args)));
+			    if (!exec_argv0) {
+				zerr("exec flag -a requires a parameter");
+				errflag = lastval = 1;
+				return;
+			    }
+			    uremnode(args, firstnode(args));
+			    break;
+			case 'c':
+			    cflags |= BINF_CLEARENV;
+			    break;
+			case 'l':
+			    cflags |= BINF_DASH;
+			    break;
+			default:
+			    zerr("unknown exec flag -%c", *cmdopt);
+			    errflag = lastval = 1;
+			    return;
+			}
+		    }
+		    next = (char *) getdata(nextnode(firstnode(args)));
+		}
+		if (exec_argv0) {
+		    char *str, *s;
+		    size_t sz = strlen(exec_argv0);
+		    str = s = zalloc(5 + 1 + sz + 1);
+		    strcpy(s, "ARGV0=");
+		    s+=6;
+		    strcpy(s, exec_argv0);
+		    zputenv(str);
+		}
+	    }
 	    uremnode(args, firstnode(args));
 	    hn = NULL;
 	    if ((cflags & BINF_COMMAND) && unset(POSIXBUILTINS))
@@ -2726,7 +2776,7 @@
 		    zsfree(STTYval);
 		    STTYval = 0;
 		}
-		execute(args, cflags & BINF_DASH, use_defpath);
+		execute(args, cflags, use_defpath);
 	    } else {		/* ( ... ) */
 		DPUTS(varspc,
 		      "BUG: assignment before complex command");
diff -ur zsh-head/Src/zsh.h zsh-exec/Src/zsh.h
--- zsh-head/Src/zsh.h	Thu Mar 29 14:35:39 2007
+++ zsh-exec/Src/zsh.h	Mon Apr 30 16:32:26 2007
@@ -1143,6 +1143,7 @@
 #define BINF_KEEPNUM		(1<<13) /* `[-+]NUM' can be an option */
 #define BINF_SKIPDASH		(1<<14) /* Treat `-' as argument (maybe `+') */
 #define BINF_DASHDASHVALID	(1<<15) /* Handle `--' even if SKIPINVALD */
+#define BINF_CLEARENV		(1<<16) /* new process started with cleared env */
 
 struct module {
     char *nam;