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Message-ID: <20160308172650.GE9349@brightrain.aerifal.cx>
Date: Tue, 8 Mar 2016 12:26:50 -0500
From: "Rich Felker (dalias@...c.org)" <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: RE: [PATCH] MIPS64 atomic_arch.h Clang complains about
input type
On Tue, Mar 08, 2016 at 12:26:13PM +0100, Szabolcs Nagy wrote:
> * Jaydeep Patil <Jaydeep.Patil@...tec.com> [2016-03-08 10:09:43 +0000]:
> >
> > ./arch/mips64/atomic_arch.h:37:29: error: unsupported inline asm: input with type 'long *' matching output with type 'int'
> >
>
> clang probably should not complain about this
>
> (it's possible to have the output in the low 32bit of a 64bit input reg
> and then you do want mismatching input/output types for the same reg)
I can imagine it being problematic on other archs where the register
names are different for 32-bit and 64-bit versions -- %0 couldn't
expand to both. Isn't there a similar ugly issue on aarch64's
atomic_arch.h?
> > #define a_sc_p a_sc_p
> > -static inline int a_sc_p(volatile long *p, void *v)
> > +static inline void *a_sc_p(volatile long *p, void *v)
> > {
> > - int r;
> > + void *r;
> > __asm__ __volatile__ (
> > "scd %0, %1"
> > : "=r"(r), "=m"(*p) : "0"(v) : "memory");
>
> the return type should be int (1 on success, 0 on failure)
>
> e.g. you can use 'long r' instead of 'int r'
>
> if clang still complains then maybe
>
> union {void *v; long r;} u = {v};
> __asm__ __volatile__ (
> "scd %0, %1" : "+r"(u.v), "=m"(*p) :: "memory");
> return u.r;
If simply using 'long' works, I think that's the cleanest/simplest
solution. The union is uglier and less obvious what it's doing so I'd
rather avoid it if we can.
Rich
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