Fix a getcwd(3) bug and make our tests run correctly under valgrind.

The getcwd(3) bug was found by valgrind.

Bug: 7291287
Change-Id: I59f3bff1c1392a408b905934eebcd5d894d37492

libc/bionic/getcwd.cpp

@@ -40,22 +40,23 @@ char* getcwd(char* buf, size_t size) {
 
   // Allocate a buffer if necessary.
   char* allocated_buf = NULL;
+  size_t allocated_size = size;
   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();
+      allocated_size = getpagesize();
     }
     buf = allocated_buf = static_cast<char*>(malloc(allocated_size));
     if (buf == NULL) {
-      // malloc set errno.
+      // malloc should set errno, but valgrind's malloc wrapper doesn't.
+      errno = ENOMEM;
       return NULL;
     }
   }
 
   // Ask the kernel to fill our buffer.
-  int rc = __getcwd(buf, size);
+  int rc = __getcwd(buf, allocated_size);
   if (rc == -1) {
     free(allocated_buf);
     // __getcwd set errno.

tests/dlopen_test.cpp

@@ -88,7 +88,7 @@ TEST(dlopen, dladdr) {
     uintptr_t start = strtoul(line, 0, 16);
     line[strlen(line) - 1] = '\0'; // Chomp the '\n'.
     char* path = strchr(line, '/');
-    if (strcmp(executable_path, path) == 0) {
+    if (path != NULL && strcmp(executable_path, path) == 0) {
       base_address = reinterpret_cast<void*>(start);
       break;
     }