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Message-ID: <CAMn1gO5A6NNd04HRX3fApRSugaM83eOqj_r7o2oegvDdRs4YeQ@mail.gmail.com>
Date: Mon, 6 Feb 2023 17:15:08 -0800
From: Peter Collingbourne <pcc@...gle.com>
To: Rich Felker <dalias@...c.org>
Cc: Markus Wichmann <nullplan@....net>, musl@...ts.openwall.com
Subject: Re: [PATCH] arm: Use __WCHAR_TYPE__ for wchar_t if defined
On Sun, Feb 5, 2023 at 3:49 PM Rich Felker <dalias@...c.org> wrote:
>
> 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.
Thanks, I agree with this and the other replies that I got. It did
seem at first that musl could be used unmodified in projects that
build with -fshort-wchar, but given the implications of a UTF-16
wchar_t for the code that implements <wchar.h>, it makes more sense
for this flag to be unsupported by musl and for any utilizing projects
to be fixed to not require -fshort-wchar.
Currently we accidentally "support" -fshort-wchar on architectures
that happen to use __WCHAR_TYPE__ to define wchar_t. Would it make
sense to add something like a static assert to alltypes.h that checks
that sizeof(wchar_t) >= 4?
Peter
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