am c80ca54f: am 60ef95e1: Merge "Enhance getcwd(3) to handle NULL like glibc."

* commit 'c80ca54f3cd2d7e20770e286f4478fb589742478':
  Enhance getcwd(3) to handle NULL like glibc.

libc/Android.mk

@@ -17,7 +17,6 @@ libc_common_src_files := \
 	unistd/fstatfs.c \
 	unistd/ftime.c \
 	unistd/ftok.c \
-	unistd/getcwd.c \
 	unistd/getdtablesize.c \
 	unistd/gethostname.c \
 	unistd/getopt_long.c \
@@ -275,6 +274,7 @@ libc_common_src_files := \
 	bionic/fdprintf.c \
 	bionic/fork.c \
 	bionic/fts.c \
+	bionic/getcwd.cpp \
 	bionic/if_nametoindex.c \
 	bionic/if_indextoname.c \
 	bionic/ioctl.c \

libc/bionic/getcwd.cpp

@@ -25,16 +25,52 @@
  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
+
 #include <unistd.h>
 #include <errno.h>
 
-extern int __getcwd(char * buf, size_t size);
+extern "C" int __getcwd(char* buf, size_t size);
 
-char *getcwd(char *buf, size_t size)
-{
-  if (buf == NULL || size == 0) {
+char* getcwd(char* buf, size_t size) {
+  // You can't specify size 0 unless you're asking us to allocate for you.
+  if (buf != NULL && size == 0) {
     errno = EINVAL;
     return NULL;
   }
-  return ( __getcwd(buf, size) < 0 ) ? NULL : buf;
+
+  // Allocate a buffer if necessary.
+  char* allocated_buf = NULL;
+  if (buf == NULL) {
+    size_t allocated_size = size;
+    if (size == 0) {
+      // The Linux kernel won't return more than a page, so translate size 0 to 4KiB.
+      // TODO: if we need to support paths longer than that, we'll have to walk the tree ourselves.
+      size = getpagesize();
+    }
+    buf = allocated_buf = reinterpret_cast<char*>(malloc(allocated_size));
+    if (buf == NULL) {
+      // malloc set errno.
+      return NULL;
+    }
+  }
+
+  // Ask the kernel to fill our buffer.
+  int rc = __getcwd(buf, size);
+  if (rc == -1) {
+    free(allocated_buf);
+    // __getcwd set errno.
+    return NULL;
+  }
+
+  // If we allocated a whole page, only return as large an allocation as necessary.
+  if (allocated_buf != NULL) {
+    if (size == 0) {
+      buf = strdup(allocated_buf);
+      free(allocated_buf);
+    } else {
+      buf = allocated_buf;
+    }
+  }
+
+  return buf;
 }