Have pthread_attr_getstack for the main thread report RLIMIT_STACK...

...rather than just what's already mapped in. This seems somewhat
contrary to POSIX's "All pages within the stack described by stackaddr
and stacksize shall be both readable and writable by the thread", but
it's what glibc does.

Bug: 17111575

(cherry picked from commit 9e4ffa7032eaab308876b8e3da86b05c3c613878)

Change-Id: I73f219a569917b2e4546c09436d7ef5231facc07

1 files changed, 12 insertions, 19 deletions

diff --git a/tests/pthread_test.cpp b/tests/pthread_test.cpp
index 5f74e388d..65577385d 100644
--- a/tests/pthread_test.cpp
+++ b/tests/pthread_test.cpp
@@ -842,8 +842,7 @@ TEST(pthread, pthread_attr_getstack__main_thread) {
   EXPECT_EQ(stack_size, stack_size2);
 
   // What does /proc/self/maps' [stack] line say?
-  void* maps_stack_base = NULL;
-  size_t maps_stack_size = 0;
+  void* maps_stack_hi = NULL;
   FILE* fp = fopen("/proc/self/maps", "r");
   ASSERT_TRUE(fp != NULL);
   char line[BUFSIZ];
@@ -852,31 +851,25 @@ TEST(pthread, pthread_attr_getstack__main_thread) {
     char name[10];
     sscanf(line, "%" PRIxPTR "-%" PRIxPTR " %*4s %*x %*x:%*x %*d %10s", &lo, &hi, name);
     if (strcmp(name, "[stack]") == 0) {
-      maps_stack_base = reinterpret_cast<void*>(lo);
-      maps_stack_size = hi - lo;
+      maps_stack_hi = reinterpret_cast<void*>(hi);
       break;
     }
   }
   fclose(fp);
 
-#if defined(__BIONIC__)
-  // bionic thinks that the stack base and size should correspond to the mapped region.
-  EXPECT_EQ(maps_stack_base, stack_base);
-  EXPECT_EQ(maps_stack_size, stack_size);
-#else
-  // glibc doesn't give the true extent for some reason.
-#endif
+  // The stack size should correspond to RLIMIT_STACK.
+  rlimit rl;
+  ASSERT_EQ(0, getrlimit(RLIMIT_STACK, &rl));
+  EXPECT_EQ(rl.rlim_cur, stack_size);
 
-  // Both bionic and glibc agree that the high address you can compute from the returned
-  // values should match what /proc/self/maps says.
-  void* stack_end = reinterpret_cast<uint8_t*>(stack_base) + stack_size;
-  void* maps_stack_end = reinterpret_cast<uint8_t*>(maps_stack_base) + maps_stack_size;
-  EXPECT_EQ(maps_stack_end, stack_end);
+  // The high address of the /proc/self/maps [stack] region should equal stack_base + stack_size.
+  // Remember that the stack grows down (and is mapped in on demand), so the low address of the
+  // region isn't very interesting.
+  EXPECT_EQ(maps_stack_hi, reinterpret_cast<uint8_t*>(stack_base) + stack_size);
 
   //
-  // What if the rlimit is smaller than the stack's current extent?
+  // What if RLIMIT_STACK is smaller than the stack's current extent?
   //
-  rlimit rl;
   rl.rlim_cur = rl.rlim_max = 1024; // 1KiB. We know the stack must be at least a page already.
   rl.rlim_max = RLIM_INFINITY;
   ASSERT_EQ(0, setrlimit(RLIMIT_STACK, &rl));
@@ -889,7 +882,7 @@ TEST(pthread, pthread_attr_getstack__main_thread) {
   ASSERT_EQ(1024U, stack_size);
 
   //
-  // What if the rlimit isn't a whole number of pages?
+  // What if RLIMIT_STACK isn't a whole number of pages?
   //
   rl.rlim_cur = rl.rlim_max = 6666; // Not a whole number of pages.
   rl.rlim_max = RLIM_INFINITY;