[v3 PATCH 10/17] exec: Do not allocate stack string in padvance

[Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>]

Many callers of padvance immediately free the allocated string
so this patch moves the stalloc call to the caller.  Instead of
returning the allocated string, padvance now returns the length
to allocate (this may be longer than the actual string length,
even including the NUL).  For the case where we would previously
return NULL, we now return -1.

Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
---

 src/cd.c   |    8 +++++---
 src/exec.c |   26 +++++++++++++-------------
 src/exec.h |    2 +-
 src/mail.c |    7 +++++--
 src/main.c |   12 +++++-------
 5 files changed, 29 insertions(+), 26 deletions(-)

diff --git a/src/cd.c b/src/cd.c
index a4e024d..610a4fa 100644
--- a/src/cd.c
+++ b/src/cd.c
@@ -98,6 +98,7 @@ cdcmd(int argc, char **argv)
 	char c;
 	struct stat statb;
 	int flags;
+	int len;
 
 	flags = cdopt();
 	dest = *argptr;
@@ -127,9 +128,10 @@ dotdot:
 	if (!*dest)
 		dest = ".";
 	path = bltinlookup("CDPATH");
-	while (path) {
-		c = *path;
-		p = padvance(&path, dest);
+	while (p = path, (len = padvance(&path, dest)) >= 0) {
+		c = *p;
+		p = stalloc(len);
+
 		if (stat(p, &statb) >= 0 && S_ISDIR(statb.st_mode)) {
 			if (c && c != ':')
 				flags |= CD_PRINT;
diff --git a/src/exec.c b/src/exec.c
index c98f14c..04ee2ba 100644
--- a/src/exec.c
+++ b/src/exec.c
@@ -118,13 +118,13 @@ shellexec(char **argv, const char *path, int idx)
 		e = errno;
 	} else {
 		e = ENOENT;
-		while ((cmdname = padvance(&path, argv[0])) != NULL) {
+		while (padvance(&path, argv[0]) >= 0) {
+			cmdname = stackblock();
 			if (--idx < 0 && pathopt == NULL) {
 				tryexec(cmdname, argv, envp);
 				if (errno != ENOENT && errno != ENOTDIR)
 					e = errno;
 			}
-			stunalloc(cmdname);
 		}
 	}
 
@@ -182,8 +182,7 @@ repeat:
 
 const char *pathopt;
 
-char *
-padvance(const char **path, const char *name)
+int padvance(const char **path, const char *name)
 {
 	const char *p;
 	char *q;
@@ -191,7 +190,7 @@ padvance(const char **path, const char *name)
 	size_t len;
 
 	if (*path == NULL)
-		return NULL;
+		return -1;
 	start = *path;
 	for (p = start ; *p && *p != ':' && *p != '%' ; p++);
 	len = p - start + strlen(name) + 2;	/* "2" is for '/' and '\0' */
@@ -211,7 +210,7 @@ padvance(const char **path, const char *name)
 		*path = p + 1;
 	else
 		*path = NULL;
-	return stalloc(len);
+	return len;
 }
 
 
@@ -266,9 +265,9 @@ printentry(struct tblentry *cmdp)
 	idx = cmdp->param.index;
 	path = pathval();
 	do {
-		name = padvance(&path, cmdp->cmdname);
-		stunalloc(name);
+		padvance(&path, cmdp->cmdname);
 	} while (--idx >= 0);
+	name = stackblock();
 	out1str(name);
 	out1fmt(snlfmt, cmdp->rehash ? "*" : nullstr);
 }
@@ -291,6 +290,7 @@ find_command(char *name, struct cmdentry *entry, int act, const char *path)
 	int e;
 	int updatetbl;
 	struct builtincmd *bcmd;
+	int len;
 
 	/* If name contains a slash, don't use PATH or hash table */
 	if (strchr(name, '/') != NULL) {
@@ -362,8 +362,8 @@ find_command(char *name, struct cmdentry *entry, int act, const char *path)
 	e = ENOENT;
 	idx = -1;
 loop:
-	while ((fullname = padvance(&path, name)) != NULL) {
-		stunalloc(fullname);
+	while ((len = padvance(&path, name)) >= 0) {
+		fullname = stackblock();
 		idx++;
 		if (pathopt) {
 			if (prefix(pathopt, "builtin")) {
@@ -398,7 +398,7 @@ loop:
 		if (!S_ISREG(statb.st_mode))
 			continue;
 		if (pathopt) {		/* this is a %func directory */
-			stalloc(strlen(fullname) + 1);
+			stalloc(len);
 			readcmdfile(fullname);
 			if ((cmdp = cmdlookup(name, 0)) == NULL ||
 			    cmdp->cmdtype != CMDFUNCTION)
@@ -789,9 +789,9 @@ describe_command(out, command, path, verbose)
 			p = command;
 		} else {
 			do {
-				p = padvance(&path, command);
-				stunalloc(p);
+				padvance(&path, command);
 			} while (--j >= 0);
+			p = stackblock();
 		}
 		if (verbose) {
 			outfmt(
diff --git a/src/exec.h b/src/exec.h
index 9ccb305..e241b74 100644
--- a/src/exec.h
+++ b/src/exec.h
@@ -62,7 +62,7 @@ extern const char *pathopt;	/* set by padvance */
 
 void shellexec(char **, const char *, int)
     __attribute__((__noreturn__));
-char *padvance(const char **, const char *);
+int padvance(const char **, const char *);
 int hashcmd(int, char **);
 void find_command(char *, struct cmdentry *, int, const char *);
 struct builtincmd *find_builtin(const char *);
diff --git a/src/mail.c b/src/mail.c
index 02e07f7..7f9e49d 100644
--- a/src/mail.c
+++ b/src/mail.c
@@ -77,9 +77,12 @@ chkmail(void)
 	setstackmark(&smark);
 	mpath = mpathset() ? mpathval() : mailval();
 	for (mtp = mailtime; mtp < mailtime + MAXMBOXES; mtp++) {
-		p = padvance(&mpath, nullstr);
-		if (p == NULL)
+		int len;
+
+		len = padvance(&mpath, nullstr);
+		if (!len)
 			break;
+		p = stackblock();
 		if (*p == '\0')
 			continue;
 		for (q = p ; *q ; q++);
diff --git a/src/main.c b/src/main.c
index 8b35118..c87fbd7 100644
--- a/src/main.c
+++ b/src/main.c
@@ -292,20 +292,18 @@ find_dot_file(char *basename)
 	char *fullname;
 	const char *path = pathval();
 	struct stat statb;
+	int len;
 
 	/* don't try this for absolute or relative paths */
 	if (strchr(basename, '/'))
 		return basename;
 
-	while ((fullname = padvance(&path, basename)) != NULL) {
+	while ((len = padvance(&path, basename)) >= 0) {
+		fullname = stackblock();
 		if ((stat(fullname, &statb) == 0) && S_ISREG(statb.st_mode)) {
-			/*
-			 * Don't bother freeing here, since it will
-			 * be freed by the caller.
-			 */
-			return fullname;
+			/* This will be freed by the caller. */
+			return stalloc(len);
 		}
-		stunalloc(fullname);
 	}
 
 	/* not found in the PATH */
--
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