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Date: Sun, 6 Dec 2020 12:06:49 -0500
From: Rich Felker <dalias@...c.org>
To: Ariadne Conill <ariadne@...eferenced.org>
Cc: Szabolcs Nagy <nsz@...t70.net>, musl@...ts.openwall.com,
Drew DeVault <sir@...wn.com>
Subject: Re: [PATCH v2] riscv64: correct struct __ucontext name
On Sun, Dec 06, 2020 at 04:55:39PM +0000, Ariadne Conill wrote:
>
> Hello,
>
> On Sunday, December 6, 2020 5:49:25 AM MST Drew DeVault wrote:
> > On Sun Dec 6, 2020 at 3:51 AM EST, Szabolcs Nagy wrote:
> > > * Drew DeVault <sir@...wn.com> [2020-12-05 18:10:06 +0000]:
> > > > This makes it consistent with other architectures and fixes some issues
> > > > with downstream software.
> > >
> > > which software?
> > >
> > > glibc uses struct ucontext_t too and user code should use ucontext_t
> > > without struct.
>
> Some glibc architecture ports use the struct __ucontext and even struct
> ucontext names, or at least did in the past.
>
> > libucontext, which does use ucontext_t.
> >
> > In fact, the issue was more related to the type conflict with
> > ucontext.h, which declared struct __ucontext in the scope of its
> > function declarations due to the naming mismatch.
>
> glibc uses the POSIX 2004 standardized ucontext_t type in its public
> definitions. I believe musl should do the same.
This produces a compile-time error is ucontext.h is included without
the right feature test macros, since signal.h will not have defined
ucontext_t in that case. That's why the public declarations must use
the struct tag.
> As far as libucontext goes, this is increasingly moot because 0.13 will
> introduce freestanding mode which avoids the musl definitions entirely, instead
> using simplified (though ABI compatible) definitions, allowing it to not only be
> used on musl but on other libc and other OS entirely (for example, it is known
> to now build on AmigaOS and Darwin).
>
> libucontext using its own definitions is an important step toward eventually
> taking ucontext.h out of musl entirely, and providing it in libucontext
> instead, too, which I think musl should do since the ucontext API was dropped
> from POSIX.
It's still an open question whether musl will eventually add these,
but the contents of ucontext.h are independent of the implementation;
they're just function declarations. The *type* declarations are in
signal.h and are *not* dropped from POSIX, so they can't be removed.
> But right now, I think the best way forward is to leave the architecture
> headers alone and just fix the ucontext.h definitions instead. I can send a
> patch doing that if you want to focus on other things.
As described above this does not work.
Rich
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