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* [musl] [PATCH] arm: Use __WCHAR_TYPE__ for wchar_t if defined
@ 2023-02-04  6:30 Peter Collingbourne
  2023-02-04  7:08 ` alice
  0 siblings, 1 reply; 6+ messages in thread
From: Peter Collingbourne @ 2023-02-04  6:30 UTC (permalink / raw)
  To: musl; +Cc: Peter Collingbourne

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.
---
 arch/arm/bits/alltypes.h.in | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/arm/bits/alltypes.h.in b/arch/arm/bits/alltypes.h.in
index d62bd7bd..9596466b 100644
--- a/arch/arm/bits/alltypes.h.in
+++ b/arch/arm/bits/alltypes.h.in
@@ -12,8 +12,12 @@
 #define __LONG_MAX 0x7fffffffL
 
 #ifndef __cplusplus
+#ifdef __WCHAR_TYPE__
+TYPEDEF __WCHAR_TYPE__ wchar_t;
+#else
 TYPEDEF unsigned wchar_t;
 #endif
+#endif
 
 TYPEDEF float float_t;
 TYPEDEF double double_t;
-- 
2.39.1.519.gcb327c4b5f-goog


^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [musl] [PATCH] arm: Use __WCHAR_TYPE__ for wchar_t if defined
  2023-02-04  6:30 [musl] [PATCH] arm: Use __WCHAR_TYPE__ for wchar_t if defined Peter Collingbourne
@ 2023-02-04  7:08 ` alice
  2023-02-05 20:00   ` Markus Wichmann
  0 siblings, 1 reply; 6+ messages in thread
From: alice @ 2023-02-04  7:08 UTC (permalink / raw)
  To: musl; +Cc: Peter Collingbourne

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.

> ---
>  arch/arm/bits/alltypes.h.in | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/arch/arm/bits/alltypes.h.in b/arch/arm/bits/alltypes.h.in
> index d62bd7bd..9596466b 100644
> --- a/arch/arm/bits/alltypes.h.in
> +++ b/arch/arm/bits/alltypes.h.in
> @@ -12,8 +12,12 @@
>  #define __LONG_MAX 0x7fffffffL
>  
>  #ifndef __cplusplus
> +#ifdef __WCHAR_TYPE__
> +TYPEDEF __WCHAR_TYPE__ wchar_t;
> +#else
>  TYPEDEF unsigned wchar_t;
>  #endif
> +#endif
>  
>  TYPEDEF float float_t;
>  TYPEDEF double double_t;
> -- 
> 2.39.1.519.gcb327c4b5f-goog


^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [musl] [PATCH] arm: Use __WCHAR_TYPE__ for wchar_t if defined
  2023-02-04  7:08 ` alice
@ 2023-02-05 20:00   ` Markus Wichmann
  2023-02-05 23:49     ` Rich Felker
  0 siblings, 1 reply; 6+ messages in thread
From: Markus Wichmann @ 2023-02-05 20:00 UTC (permalink / raw)
  To: musl; +Cc: Peter Collingbourne

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.

Ciao,
Markus

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [musl] [PATCH] arm: Use __WCHAR_TYPE__ for wchar_t if defined
  2023-02-05 20:00   ` Markus Wichmann
@ 2023-02-05 23:49     ` Rich Felker
  2023-02-07  1:15       ` Peter Collingbourne
  0 siblings, 1 reply; 6+ messages in thread
From: Rich Felker @ 2023-02-05 23:49 UTC (permalink / raw)
  To: Markus Wichmann; +Cc: musl, Peter Collingbourne

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

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [musl] [PATCH] arm: Use __WCHAR_TYPE__ for wchar_t if defined
  2023-02-05 23:49     ` Rich Felker
@ 2023-02-07  1:15       ` Peter Collingbourne
  2023-02-07 14:59         ` Rich Felker
  0 siblings, 1 reply; 6+ messages in thread
From: Peter Collingbourne @ 2023-02-07  1:15 UTC (permalink / raw)
  To: Rich Felker; +Cc: Markus Wichmann, musl

On Sun, Feb 5, 2023 at 3:49 PM Rich Felker <dalias@libc.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

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [musl] [PATCH] arm: Use __WCHAR_TYPE__ for wchar_t if defined
  2023-02-07  1:15       ` Peter Collingbourne
@ 2023-02-07 14:59         ` Rich Felker
  0 siblings, 0 replies; 6+ messages in thread
From: Rich Felker @ 2023-02-07 14:59 UTC (permalink / raw)
  To: Peter Collingbourne; +Cc: Markus Wichmann, musl

On Mon, Feb 06, 2023 at 05:15:08PM -0800, Peter Collingbourne wrote:
> On Sun, Feb 5, 2023 at 3:49 PM Rich Felker <dalias@libc.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?

If you count target-specific options, GCC probably has hundreds of
options that produce incompatible/broken ABIs. We certainly don't have
the means to trap all or even most of them. In the case of most,
including -fshort-wchar, GCC documents this:

    "Warning: the -fshort-wchar switch causes GCC to generate code
    that is not binary compatible with code generated without that
    switch. Use it to conform to a non-default application binary
    interface."

so I don't really think any action is needed.

Rich

^ permalink raw reply	[flat|nested] 6+ messages in thread

end of thread, other threads:[~2023-02-07 14:59 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2023-02-04  6:30 [musl] [PATCH] arm: Use __WCHAR_TYPE__ for wchar_t if defined Peter Collingbourne
2023-02-04  7:08 ` alice
2023-02-05 20:00   ` Markus Wichmann
2023-02-05 23:49     ` Rich Felker
2023-02-07  1:15       ` Peter Collingbourne
2023-02-07 14:59         ` Rich Felker

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