kbuild: stop docproc segfaulting when SRCTREE isn't set.

Prevent docproc from segfaulting when SRCTREE isn't set.
Signed-off-by: Rob Landley <rob@landley.net>
Acked-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

scripts/basic/docproc.c

@@ -66,12 +66,15 @@ FILELINE * entity_system;
 #define FUNCTION      "-function"
 #define NOFUNCTION    "-nofunction"
 
+char *srctree;
+
 void usage (void)
 {
 	fprintf(stderr, "Usage: docproc {doc|depend} file\n");
 	fprintf(stderr, "Input is read from file.tmpl. Output is sent to stdout\n");
 	fprintf(stderr, "doc: frontend when generating kernel documentation\n");
 	fprintf(stderr, "depend: generate list of files referenced within file\n");
+	fprintf(stderr, "Environment variable SRCTREE: absolute path to kernel source tree.\n");
 }
 
 /*
@@ -90,7 +93,7 @@ void exec_kernel_doc(char **svec)
 			exit(1);
 		case  0:
 			memset(real_filename, 0, sizeof(real_filename));
-			strncat(real_filename, getenv("SRCTREE"), PATH_MAX);
+			strncat(real_filename, srctree, PATH_MAX);
 			strncat(real_filename, KERNELDOCPATH KERNELDOC,
 					PATH_MAX - strlen(real_filename));
 			execvp(real_filename, svec);
@@ -171,7 +174,7 @@ void find_export_symbols(char * filename)
 	if (filename_exist(filename) == NULL) {
 		char real_filename[PATH_MAX + 1];
 		memset(real_filename, 0, sizeof(real_filename));
-		strncat(real_filename, getenv("SRCTREE"), PATH_MAX);
+		strncat(real_filename, srctree, PATH_MAX);
 		strncat(real_filename, filename,
 				PATH_MAX - strlen(real_filename));
 		sym = add_new_file(filename);
@@ -338,6 +341,10 @@ void parse_file(FILE *infile)
 int main(int argc, char *argv[])
 {
 	FILE * infile;
+
+	srctree = getenv("SRCTREE");
+	if (!srctree)
+		srctree = getcwd(NULL, 0);
 	if (argc != 3) {
 		usage();
 		exit(1);