Surprising allocation in windows/compat.rs is a footgun for custom allocators

[Diggsey]

This function is the problem:

rust/library/std/src/sys/windows/compat.rs

Lines 17 to 28 in f5230fb

	pub fn lookup(module: &str, symbol: &str) -> Option<usize> {
	let mut module: Vec<u16> = module.encode_utf16().collect();
	module.push(0);
	let symbol = CString::new(symbol).unwrap();
	unsafe {
	let handle = c::GetModuleHandleW(module.as_ptr());
	match c::GetProcAddress(handle, symbol.as_ptr()) as usize {
	0 => None,
	n => Some(n),
	}
	}
	}

AcquireSRWLockExclusive is one of the functions utilizing this compatibility layer. However, most custom allocators indirectly rely on this function.

This means that allocators must be re-entrant, which is essentially impossible since re-entrancy detection requires thread-local storage, which in turn calls AcquireSRWLockExclusive.

For some reason I haven't been able to fathom, this does not always result in a crash, so many custom allocators which rely on TLS appear to work. However, seemingly inconsequential changes (such as changing the size of a struct) result in the program crashing with an access violation or stack overflow.

The fix is to remove this allocation and encode these strings at compile-time.

[RalfJung]

Another fix might be to remove the compat layer, at least for locks -- which is possible once support for Windows XP is dropped (something that is discussed every now and then, and just recently came up on Zulip again I think).

[sivadeilra]

Btw, this PR: #81250 will remove the need for many of these.

[m-ou-se]

If we can do the conversion (to nul-terminated utf16 for the module name, and nul-terminated ascii/utf8 for the function name) at compile time, this wouldn't need to allocate at all. For the function name, this can be as simple as just a concat!(stringify!($symbol), "\0"). The other one is a bit more effort.

[sivadeilra]

We can use GetModuleHandleA instead of GetModuleHandleW. That way, the module name can be UTF-8, so can be constant.

[m-ou-se]

#81478 fixed this.