Re: [PATCH 3/5] rust: sync: support using bool with READ_ONCE

[Peter Zijlstra]

On Tue, Jan 06, 2026 at 06:12:01PM +0000, Gary Guo wrote:
> On Tue, 6 Jan 2026 13:43:26 +0100
> Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:

> > Does this hardcode that sizeof(_Bool) == 1? There are ABIs where this is
> > not the case.
> 
> Hi Peter,
> 
> Do you have a concrete example on which ABI/arch this is not true?
> 
> I know that the C spec doesn't mandate _Bool and char are of the same size
> but we have tons of assumptions that is not guaranteed by standard C..

Darwin/PowerPC famously has sizeof(_Bool) == 4

Win32: Visual C++ 4.2 (and earlier) had sizeof(bool)==4 (they mapped
bool to int), while Visual C++ 5.0 introduced a native _Bool and moved
to 1 byte.

Early RISC CPUs (MIPS, PowerPC, Alpha) had severe penalties for byte
access and their compilers would've had sizeof(bool)=={4,8}.

I think AVR/Arduino also has sizeof(bool) == sizeof(int) which is 2.