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Improve SGX RWLock initializer test #76278

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Sep 14, 2020
Merged

Improve SGX RWLock initializer test #76278

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34 changes: 11 additions & 23 deletions library/std/src/sys/sgx/rwlock/tests.rs
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Original file line number Diff line number Diff line change
@@ -1,14 +1,12 @@
use super::*;
use crate::mem::{self, MaybeUninit};
use core::array::FixedSizeArray;

// Verify that the bytes of initialized RWLock are the same as in
// libunwind. If they change, `src/UnwindRustSgx.h` in libunwind needs to
// be changed too.
// Verify that the byte pattern libunwind uses to initialize an RWLock is
// equivalent to the value of RWLock::new(). If the value changes,
// `src/UnwindRustSgx.h` in libunwind needs to be changed too.
#[test]
fn test_c_rwlock_initializer() {
#[rustfmt::skip]
const RWLOCK_INIT: &[u8] = &[
const C_RWLOCK_INIT: &[u8] = &[
/* 0x00 */ 0x1, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
/* 0x10 */ 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x2, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
/* 0x20 */ 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
Expand All @@ -20,24 +18,14 @@ fn test_c_rwlock_initializer() {
/* 0x80 */ 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
];

#[inline(never)]
fn zero_stack() {
test::black_box(MaybeUninit::<[RWLock; 16]>::zeroed());
}

#[inline(never)]
unsafe fn rwlock_new(init: &mut MaybeUninit<RWLock>) {
init.write(RWLock::new());
}
// For the test to work, we need the padding/unused bytes in RWLock to be
// initialized as 0. In practice, this is the case with statics.
static RUST_RWLOCK_INIT: RWLock = RWLock::new();

unsafe {
// try hard to make sure that the padding/unused bytes in RWLock
// get initialized as 0. If the assertion below fails, that might
// just be an issue with the test code and not with the value of
// RWLOCK_INIT.
zero_stack();
let mut init = MaybeUninit::<RWLock>::zeroed();
rwlock_new(&mut init);
assert_eq!(mem::transmute::<_, [u8; 144]>(init.assume_init()).as_slice(), RWLOCK_INIT)
// If the assertion fails, that not necessarily an issue with the value
// of C_RWLOCK_INIT. It might just be an issue with the way padding
// bytes are initialized in the test code.
assert_eq!(&crate::mem::transmute_copy::<_, [u8; 144]>(&RUST_RWLOCK_INIT), C_RWLOCK_INIT);
};
}