Re: [musl] [PATCH] arm: Use __WCHAR_TYPE__ for wchar_t if defined

[Rich Felker <dalias@libc.org>]

On Sun, Feb 05, 2023 at 09:00:03PM +0100, Markus Wichmann wrote:
> On Sat, Feb 04, 2023 at 08:08:36AM +0100, alice wrote:
> > On Sat Feb 4, 2023 at 7:30 AM CET, Peter Collingbourne wrote:
> > > When building with -fshort-wchar the definition of wchar_t is
> > > incorrect. Get the correct definition from the compiler if available.
> > >
> > > This is useful when reusing the freestanding parts of musl on a
> > > bare-metal target that uses -fshort-wchar.
> >
> > somebody talked about this in 2015, see
> > https://www.openwall.com/lists/musl/2015/02/18/2
> > for the previous discussion.
> >
> > i understand in this case it's proposed a little different-
> > "reusing freestanding parts" as opposed to building a whole libc.so, but in
> > that case you could most likely patch this in when reusing it standalone only?
> >
> > it doesn't seem a good idea for it to be there, in general.
> 
> Seconded. A lot of code in musl depends on wchar_t being able to hold
> the current maximum Unicode codepoint of 0x10FFFF at least, so the type
> must be at least 21 bits.

Absolutely. -fshort-wchar requests a different ABI that is
fundamentally incompatible with libc and with use of the libc headers,
and also fundamentally incompatible with Unicode and the requirements
of the C language (unless you only want to support the BMP) -- C does
not allow "multi-wchar_t characters".

If you're targeting freestanding environment not using libc, you
should use -nostdinc and provide headers suitable to your environment
instead of the libc ones. But really you should fix the offending code
not to use wchar_t for UTF-16, and not use -fshort-wchar. Modern C has
a char16_t type for this purpose.

Rich