Use __attribute__((noreturn)) for function pointer

Submitted by Matthew Maurer on June 14, 2019, 4:50 p.m.

Details

Message ID CAGSQo0113zEc-nKUFL-yznG9R_hgTpH1EJ5Q8rB8aD=A-yuZkQ@mail.gmail.com
State New
Series "Use __attribute__((noreturn)) for function pointer"
Headers show

Commit Message

Matthew Maurer June 14, 2019, 4:50 p.m.
Done.

On Fri, Jun 14, 2019 at 9:47 AM Rich Felker <dalias@libc.org> wrote:

> On Fri, Jun 14, 2019 at 09:42:09AM -0700, Matthew Maurer wrote:
> > _Noreturn doesn't actually exist in C99 - that's a C11ism. Even in C11,
> it
> > cannot be used on a function pointer type.
> > __attribute__((noreturn)) is a GNU C extension (which we're allowed to
> use,
> > unlike C11), and is allowed to be placed on function pointer types.
>
> > From adeca3acc1e4c1b727e8524542c201b436ba8a5b Mon Sep 17 00:00:00 2001
> > From: Matthew Maurer <mmaurer@google.com>
> > Date: Thu, 13 Jun 2019 12:33:38 -0700
> > Subject: [PATCH] Use __attribute__((noreturn)) for function pointer
> >
> > _Noreturn is a C11 construct, and may only be used at the site of a
> > function definition.
> > __attribute__((noreturn)) is a GNU C extension which may be used on
> > function pointers.
> > GCC with any standard permits _Noreturn in the position it's used
> > (likely because it implements it in terms of attribute noreturn), but
> > Clang will reject it for any standard past C11, and warn pre-C11.
> >
> > Musl is written in C99 with GNU C extensions, so
> > __attribute__((noreturn)) is both more correct in that sense and allows
> > us to compile with Clang set to higher language standards.
> > ---
> >  src/internal/dynlink.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/src/internal/dynlink.h b/src/internal/dynlink.h
> > index cbe0a6fe..d2bf6b41 100644
> > --- a/src/internal/dynlink.h
> > +++ b/src/internal/dynlink.h
> > @@ -95,7 +95,7 @@ struct fdpic_dummy_loadmap {
> >  #define DYN_CNT 32
> >
> >  typedef void (*stage2_func)(unsigned char *, size_t *);
> > -typedef _Noreturn void (*stage3_func)(size_t *);
> > +typedef __attribute__((noreturn)) void (*stage3_func)(size_t *);
> >
> >  hidden void *__dlsym(void *restrict, const char *restrict, void
> *restrict);
> >
> > --
> > 2.22.0.410.gd8fdbe21b5-goog
> >
>
> Just remove it. There's no sense having nonstandard C here for
> something that's completely inconsequential. It wasn't important, and
> probably the only reason I wrote it was wrongly thinking the function
> pointer type had to match the _Noreturn of the function definition.
>
> Rich
>

Patch hide | download patch | download mbox

From f31e064e7b2175e5a20552b6b2a627f5411d9b9f Mon Sep 17 00:00:00 2001
From: Matthew Maurer <mmaurer@google.com>
Date: Thu, 13 Jun 2019 12:33:38 -0700
Subject: [PATCH] Do not use _Noreturn for a function pointer

_Noreturn is a C11 construct, and may only be used at the site of a
function definition.
---
 src/internal/dynlink.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/internal/dynlink.h b/src/internal/dynlink.h
index cbe0a6fe..165bbedb 100644
--- a/src/internal/dynlink.h
+++ b/src/internal/dynlink.h
@@ -95,7 +95,7 @@  struct fdpic_dummy_loadmap {
 #define DYN_CNT 32
 
 typedef void (*stage2_func)(unsigned char *, size_t *);
-typedef _Noreturn void (*stage3_func)(size_t *);
+typedef void (*stage3_func)(size_t *);
 
 hidden void *__dlsym(void *restrict, const char *restrict, void *restrict);
 
-- 
2.22.0.410.gd8fdbe21b5-goog


Comments

Rich Felker June 25, 2019, 10:58 p.m.
On Fri, Jun 14, 2019 at 09:50:45AM -0700, Matthew Maurer wrote:
> Done.
> 
> On Fri, Jun 14, 2019 at 9:47 AM Rich Felker <dalias@libc.org> wrote:
> 
> > On Fri, Jun 14, 2019 at 09:42:09AM -0700, Matthew Maurer wrote:
> > > _Noreturn doesn't actually exist in C99 - that's a C11ism. Even in C11,
> > it
> > > cannot be used on a function pointer type.
> > > __attribute__((noreturn)) is a GNU C extension (which we're allowed to
> > use,
> > > unlike C11), and is allowed to be placed on function pointer types.
> >
> > > From adeca3acc1e4c1b727e8524542c201b436ba8a5b Mon Sep 17 00:00:00 2001
> > > From: Matthew Maurer <mmaurer@google.com>
> > > Date: Thu, 13 Jun 2019 12:33:38 -0700
> > > Subject: [PATCH] Use __attribute__((noreturn)) for function pointer
> > >
> > > _Noreturn is a C11 construct, and may only be used at the site of a
> > > function definition.
> > > __attribute__((noreturn)) is a GNU C extension which may be used on
> > > function pointers.
> > > GCC with any standard permits _Noreturn in the position it's used
> > > (likely because it implements it in terms of attribute noreturn), but
> > > Clang will reject it for any standard past C11, and warn pre-C11.
> > >
> > > Musl is written in C99 with GNU C extensions, so
> > > __attribute__((noreturn)) is both more correct in that sense and allows
> > > us to compile with Clang set to higher language standards.
> > > ---
> > >  src/internal/dynlink.h | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/src/internal/dynlink.h b/src/internal/dynlink.h
> > > index cbe0a6fe..d2bf6b41 100644
> > > --- a/src/internal/dynlink.h
> > > +++ b/src/internal/dynlink.h
> > > @@ -95,7 +95,7 @@ struct fdpic_dummy_loadmap {
> > >  #define DYN_CNT 32
> > >
> > >  typedef void (*stage2_func)(unsigned char *, size_t *);
> > > -typedef _Noreturn void (*stage3_func)(size_t *);
> > > +typedef __attribute__((noreturn)) void (*stage3_func)(size_t *);
> > >
> > >  hidden void *__dlsym(void *restrict, const char *restrict, void
> > *restrict);
> > >
> > > --
> > > 2.22.0.410.gd8fdbe21b5-goog
> > >
> >
> > Just remove it. There's no sense having nonstandard C here for
> > something that's completely inconsequential. It wasn't important, and
> > probably the only reason I wrote it was wrongly thinking the function
> > pointer type had to match the _Noreturn of the function definition.

> From f31e064e7b2175e5a20552b6b2a627f5411d9b9f Mon Sep 17 00:00:00 2001
> From: Matthew Maurer <mmaurer@google.com>
> Date: Thu, 13 Jun 2019 12:33:38 -0700
> Subject: [PATCH] Do not use _Noreturn for a function pointer
> 
> _Noreturn is a C11 construct, and may only be used at the site of a
> function definition.
> ---
>  src/internal/dynlink.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/src/internal/dynlink.h b/src/internal/dynlink.h
> index cbe0a6fe..165bbedb 100644
> --- a/src/internal/dynlink.h
> +++ b/src/internal/dynlink.h
> @@ -95,7 +95,7 @@ struct fdpic_dummy_loadmap {
>  #define DYN_CNT 32
>  
>  typedef void (*stage2_func)(unsigned char *, size_t *);
> -typedef _Noreturn void (*stage3_func)(size_t *);
> +typedef void (*stage3_func)(size_t *);
>  
>  hidden void *__dlsym(void *restrict, const char *restrict, void *restrict);
>  
> -- 
> 2.22.0.410.gd8fdbe21b5-goog
> 

I've had this in my local tree for a while, but hadn't built it
(didn't think I had to), and noticed that removing the _Noreturn from
the type but not from __dls2b and __dls3 caused warnings (errors with
my local -Werror) for "_Noreturn function returns". So I'm amending
this to also remove the _Noreturn from the definitions of these
functions, since it serves no purpose anyway. Now I think the only
remaining uses of _Noreturn are on public interfaces that are really
supposed to be _Noreturn.

Rich