Re-enable test/guard.test

* Fix compilation warnings on abs()
* Fix problems on OS X and CentOS 6
* Disable this test with -DENABLE_GCOV=ON

Closes #2429

test/unit/CMakeLists.txt

@@ -70,8 +70,11 @@ target_link_libraries(xrow.test server misc ${MSGPUCK_LIBRARIES})
 add_executable(fiber.test fiber.cc unit.c)
 target_link_libraries(fiber.test core)
 
-add_executable(guard.test guard.cc unit.c)
-target_link_libraries(guard.test core)
+if (NOT ENABLE_GCOV)
+    # This test is known to be broken with GCOV
+    add_executable(guard.test guard.cc unit.c)
+    target_link_libraries(guard.test core)
+endif ()
 
 add_executable(fiber_stress.test fiber_stress.cc)
 target_link_libraries(fiber_stress.test core)

test/unit/guard.cc

@@ -9,34 +9,40 @@ sigsegf_handler(int signo)
 	exit(0);
 }
 
-static void
-stack_break_f(void *ptr)
+static int __attribute__((noinline))
+stack_break_f(char *ptr)
 {
 	char block[2048];
-	memset(block, 0, 2048);
-	if (abs((char *)ptr - block) < 65536)
-		stack_break_f(ptr);
+	char sum = 0;
+	memset(block, 0xff, 2048);
+	sum += block[block[4]];
+	ptrdiff_t stack_diff = ptr > block ? ptr - block : block - ptr;
+	if (stack_diff < 65536)
+		sum += stack_break_f(ptr);
+	return sum;
 }
 
+static char stack_buf[SIGSTKSZ];
+
 static int
 main_f(va_list ap)
 {
-	char stack_buf[SIGSTKSZ];
 	stack_t stack;
 	stack.ss_sp = stack_buf;
 	stack.ss_size = SIGSTKSZ;
-	stack.ss_flags = SS_ONSTACK;
+	stack.ss_flags = 0;
 	sigaltstack(&stack, NULL);
 	struct sigaction sa;
 	sa.sa_handler = sigsegf_handler;
 	sigemptyset(&sa.sa_mask);
 	sa.sa_flags = SA_ONSTACK;
 	sigaction(SIGSEGV, &sa, NULL);
+	sigaction(SIGBUS, &sa, NULL);
 
-	stack_break_f(&stack);
+	int res = stack_break_f((char *)&stack);
 
 	ev_break(loop(), EVBREAK_ALL);
-	return 0;
+	return res;
 }
 
 int main()

test/unit/suite.ini

 [default]
 core = unittest
 description = unit tests
-disabled = guard.test
 is_parallel = True