Fix the WIFSTOPPED definition.

Although this breaks job control in several shells (including mksh),
this has been broken since the initial commit and no-one's noticed until
now.

Bug: android/ndk#1878
Test: treehugger
Change-Id: Id7c4805965c5e5847db99b57df1af13355adcc22

libc/include/bits/wait.h

@@ -53,7 +53,7 @@
 #define WIFEXITED(__status) (WTERMSIG(__status) == 0)
 
 /** Returns true if the process was stopped by a signal. */
-#define WIFSTOPPED(__status) (WTERMSIG(__status) == 0x7f)
+#define WIFSTOPPED(__status) (((__status) & 0xff) == 0x7f)
 
 /** Returns true if the process was terminated by a signal. */
 #define WIFSIGNALED(__status) (WTERMSIG((__status)+1) >= 2)

tests/sys_wait_test.cpp

@@ -42,3 +42,22 @@ TEST(sys_wait, waitid) {
   ASSERT_EQ(66, si.si_status);
   ASSERT_EQ(CLD_EXITED, si.si_code);
 }
+
+// https://github.com/android/ndk/issues/1878
+TEST(sys_wait, macros) {
+#if defined(__GLIBC__)
+  // glibc before 2016 requires an lvalue.
+#else
+  ASSERT_FALSE(WIFEXITED(0x7f));
+  ASSERT_TRUE(WIFSTOPPED(0x7f));
+  ASSERT_FALSE(WIFCONTINUED(0x7f));
+
+  ASSERT_TRUE(WIFEXITED(0x80));
+  ASSERT_FALSE(WIFSTOPPED(0x80));
+  ASSERT_FALSE(WIFCONTINUED(0x80));
+
+  ASSERT_FALSE(WIFEXITED(0xffff));
+  ASSERT_FALSE(WIFSTOPPED(0xffff));
+  ASSERT_TRUE(WIFCONTINUED(0xffff));
+#endif
+}