memunreachable_test: don't use `write` to escape addresses
A recent change
(https://android-review.googlesource.com/c/platform/bionic/+/961601)
caused this test to fail. This change allowed LLVM to optimize what was
previously `__write_chk` into a standard call to `write`.
LLVM knows things about `write`. In particular, it knows that `write`
doesn't capture its buffer param, which `Ref` assumes isn't possible.
LLVM can't reason much about `volatile` operations; storing this to a
`volatile` ptr should be good enough. If not, there are a few other
tricks we can play here.
Bug: 133479661
Test: `atest
memunreachable_test:memunreachable_test.MemunreachableTest#stack --
--abi x86` on internal-master
Change-Id: I905e510210cafdf83fa1b50f2f090d4f8b9653da
diff --git a/libmemunreachable/tests/MemUnreachable_test.cpp b/libmemunreachable/tests/MemUnreachable_test.cpp
index bba0c6d..024b6bc 100644
--- a/libmemunreachable/tests/MemUnreachable_test.cpp
+++ b/libmemunreachable/tests/MemUnreachable_test.cpp
@@ -47,7 +47,8 @@
// Trick the compiler into thinking a value on the stack is still referenced.
static void Ref(void** ptr) {
- write(0, ptr, 0);
+ void** volatile storage;
+ storage = ptr;
}
class MemunreachableTest : public ::testing::Test {