Re: [PATCH v3] libgo: Don't use pt_regs member in mcontext_t

[Rich Felker <dalias@libc.org>]

On Mon, Mar 07, 2022 at 02:59:02PM -0800, Ian Lance Taylor wrote:
> On Sun, Mar 6, 2022 at 11:11 PM <soeren@soeren-tempel.net> wrote:
> >
> > +#ifdef __PPC64__
> > +       ret.sigpc = ((ucontext_t*)(context))->uc_mcontext.gp_regs[32];
> > +#else
> > +       ret.sigpc = ((ucontext_t*)(context))->uc_mcontext.gregs[32];
> > +#endif
> 
> Have you tested this in 32-bit mode?  It does not look correct based
> on the glibc definitions.  Looking at glibc it seems that it ought to
> be
> 
> reg.sigpc = ((ucontext_t*)(context))->uc_mcontext.uc_regs->gregs[32];

Indeed, I think it has to use that conditional on __GLIBC__. I was
thinking the union glibc has was an anon union, but no, it's named
uc_mcontext despite not having type mcontext_t.

Ideally glibc could fix this by doing:

    union {
        union __ctx(uc_regs_ptr) {
            struct __ctx(pt_regs) *__ctx(regs);
            mcontext_t *__ctx(uc_regs);
        } uc_mcontext;
        mcontext_t *__ctx(uc_regs);
    };

so that there would be a common API for accessing it that doesn't
conflict with the properties the standard mandates.

Rich