support null buffer argument to getcwd, auto-allocating behavior

this is a popular extension some programs depend on, and by using a
temporary buffer and strdup rather than malloc prior to the syscall,
i've avoided the dependency on free and thus minimized the bloat cost
of supporting this feature.

diff --git a/src/unistd/getcwd.c b/src/unistd/getcwd.c
index b64b560..2e540cd 100644 (file)
--- a/src/unistd/getcwd.c
+++ b/src/unistd/getcwd.c
@@ -1,8 +1,13 @@
 #include <unistd.h>
 #include <errno.h>
+#include <limits.h>
+#include <string.h>
 #include "syscall.h"
 
 char *getcwd(char *buf, size_t size)
 {
-       return syscall(SYS_getcwd, buf, size) < 0 ? NULL : buf;
+       char tmp[PATH_MAX];
+       if (!buf) buf = tmp, size = PATH_MAX;
+       if (syscall(SYS_getcwd, buf, size) < 0) return 0;
+       return buf == tmp ? strdup(buf) : buf;
 }