Add sized-delete size-checking functionality.

The existing checks are good at finding such issues (on tcache flush), but not
so good at pinpointing them.  Debug mode can find them, but sometimes debug mode
slows down a program so much that hard-to-hit bugs can take a long time to
crash.

This commit adds functionality to keep programs mostly on their fast paths,
while also checking every sized delete argument they get.

test/unit/size_check.c

@@ -0,0 +1,62 @@
+#include "test/jemalloc_test.h"
+
+#include "jemalloc/internal/safety_check.h"
+
+bool fake_abort_called;
+void fake_abort(const char *message) {
+	(void)message;
+	fake_abort_called = true;
+}
+
+#define SIZE1 SC_SMALL_MAXCLASS
+#define SIZE2 (SC_SMALL_MAXCLASS / 2)
+
+TEST_BEGIN(test_invalid_size_sdallocx) {
+	test_skip_if(!config_opt_size_checks);
+	safety_check_set_abort(&fake_abort);
+
+	fake_abort_called = false;
+	void *ptr = malloc(SIZE1);
+	assert_ptr_not_null(ptr, "Unexpected failure");
+	sdallocx(ptr, SIZE2, 0);
+	expect_true(fake_abort_called, "Safety check didn't fire");
+
+	safety_check_set_abort(NULL);
+}
+TEST_END
+
+TEST_BEGIN(test_invalid_size_sdallocx_nonzero_flag) {
+	test_skip_if(!config_opt_size_checks);
+	safety_check_set_abort(&fake_abort);
+
+	fake_abort_called = false;
+	void *ptr = malloc(SIZE1);
+	assert_ptr_not_null(ptr, "Unexpected failure");
+	sdallocx(ptr, SIZE2, MALLOCX_TCACHE_NONE);
+	expect_true(fake_abort_called, "Safety check didn't fire");
+
+	safety_check_set_abort(NULL);
+}
+TEST_END
+
+TEST_BEGIN(test_invalid_size_sdallocx_noflags) {
+	test_skip_if(!config_opt_size_checks);
+	safety_check_set_abort(&fake_abort);
+
+	fake_abort_called = false;
+	void *ptr = malloc(SIZE1);
+	assert_ptr_not_null(ptr, "Unexpected failure");
+	je_sdallocx_noflags(ptr, SIZE2);
+	expect_true(fake_abort_called, "Safety check didn't fire");
+
+	safety_check_set_abort(NULL);
+}
+TEST_END
+
+int
+main(void) {
+	return test(
+	    test_invalid_size_sdallocx,
+	    test_invalid_size_sdallocx_nonzero_flag,
+	    test_invalid_size_sdallocx_noflags);
+}