Re: From wchar_t to char32_t, new module mbszero

[Paul Eggert]

On 2023-07-17 09:53, Bruno Haible wrote:

> On NetBSD, I apparently did not locate the right source code of the mbsinit
> function, due to the complexity of the citrus code. And did not want to debug
> it, because debugging in libc code without debugging information is often
> a waste of time.

I looked into it. I think it's due to the funky business with struct 
_RuneStatePriv. There's a pointer's worth of data before the data that 
the converters see, and until recently there was another character that 
ended up perhaps needing another pointer's worth of padding.  Two 
pointers (8 bytes each), plus the 12 bytes we already saw, would explain 
the 28 bytes you observed.

I fixed mbcel.h for that by installing the attached patch into 
diffutils. Thanks for pointing it out.


> > This macro is not used anywhere. How about adding a comment explaining
> > why it's defined but not used? Or if it's not needed we can remove it.
>
> It's needed, namely as lower bound for _GL_MBSTATE_ZERO_SIZE:
> 0 < _GL_MBSTATE_INIT_SIZE <= _GL_MBSTATE_ZERO_SIZE <= sizeof (mbstate_t).

That's merely documentation, right? That is, only comments use the lower 
bound.

> And I won't write
>    sizeof (((mbstate_t) {0}).__count)
> outside of comments, since the less identifiers with double-underscore
> we use, the better.

On the other hand, the sizeof is more likely to notify builders if glibc 
changes internals in an incompatible way. (No big deal either way of 
course.)

One thing I noticed on NetBSD 9.3 x86-64 (it has GCC 7), is that it 
didn't optimize memset calls away. So in memcel.h I stuck with 
initializing by hand rather than using memset.

0001-diff-fix-mbcel-bug-on-NetBSD.patch
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