[gofrontend-dev] Re: [PATCH] libgo: include asm/ptrace.h for pt_regs definition on PowerPC

Sören Tempel soeren@soeren-tempel.net
Sun Mar 6 12:49:01 GMT 2022


What would be the benefit of using .uc_regs instead of .regs? The
current code works entirely fine as it, it just needs an include of the
Linux Kernel header defining the pt_regs type (which my proposed patch
adds).

Furthermore, it seems to me that .uc_regs is only available on powerpc
but not on power64 [1]? musl libc also only defines the .uc_regs member
for powerpc [2] and not for powerpc64 [3] on ucontext_t.

Is there any documentation for .uc_regs on PowerPC?

Sincerely,
Sören

[1]: https://github.com/torvalds/linux/blob/c3617f72036c909e1f6086b5b9e364e0ef90a6da/arch/powerpc/include/uapi/asm/ucontext.h#L24-L27
[2]: https://git.musl-libc.org/cgit/musl/tree/arch/powerpc/bits/signal.h?id=f8bdc3048216f41eaaf655524fa286cfb1184a70#n67
[3]: https://git.musl-libc.org/cgit/musl/tree/arch/powerpc64/bits/signal.h?id=f8bdc3048216f41eaaf655524fa286cfb1184a70#n56

Ian Lance Taylor <iant@golang.org> wrote:
> Note for gofrontend-dev: on gcc-patches only Andreas Schwab suggested
> using uc_regs instead of regs, which does look correct to me.
> 
> Ian
> 
> On Mon, Feb 21, 2022 at 8:47 AM Sören Tempel <soeren@soeren-tempel.net> wrote:
> >
> > Ping.
> >
> > Summary: Fix build of libgo on PPC with musl libc and libucontext by
> > explicitly including the Linux header defining `struct pt_regs` instead of
> > relying on other libc headers to include it implicitly.
> >
> > See: https://gcc.gnu.org/pipermail/gcc-patches/2022-January/587520.html
> >
> > If the patch needs to be revised further please let me know. This patch has
> > been applied at Alpine Linux downstream (which uses musl libc) for a while, I
> > have not tested it on other systems.
> >
> > Greetings,
> > Sören
> >
> > Sören Tempel <soeren@soeren-tempel.net> wrote:
> > > Both glibc and musl libc declare pt_regs as an incomplete type. This
> > > type has to be completed by inclusion of another header. On Linux, the
> > > asm/ptrace.h header file provides this type definition. Without
> > > including this header file, it is not possible to access the regs member
> > > of the mcontext_t struct as done in libgo/runtime/go-signal.c. On glibc,
> > > other headers (e.g. sys/user.h) include asm/ptrace.h but on musl
> > > asm/ptrace.h is not included by other headers and thus the
> > > aforementioned files do not compile without an explicit include of
> > > asm/ptrace.h:
> > >
> > >       libgo/runtime/go-signal.c: In function 'getSiginfo':
> > >       libgo/runtime/go-signal.c:227:63: error: invalid use of undefined type 'struct pt_regs'
> > >         227 |         ret.sigpc = ((ucontext_t*)(context))->uc_mcontext.regs->nip;
> > >             |
> > >
> > > See also:
> > >
> > > * https://git.musl-libc.org/cgit/musl/commit/?id=c2518a8efb6507f1b41c3b12e03b06f8f2317a1f
> > > * https://github.com/kaniini/libucontext/issues/36
> > >
> > > Signed-off-by: Sören Tempel <soeren@soeren-tempel.net>
> > >
> > > ChangeLog:
> > >
> > >       * libgo/runtime/go-signal.c: Include asm/ptrace.h for the
> > >         definition of pt_regs (used by mcontext_t) on PowerPC.
> > > ---
> > >  libgo/runtime/go-signal.c | 6 ++++++
> > >  1 file changed, 6 insertions(+)
> > >
> > > diff --git a/libgo/runtime/go-signal.c b/libgo/runtime/go-signal.c
> > > index d30d1603adc..fc01e04e4a1 100644
> > > --- a/libgo/runtime/go-signal.c
> > > +++ b/libgo/runtime/go-signal.c
> > > @@ -10,6 +10,12 @@
> > >  #include <sys/time.h>
> > >  #include <ucontext.h>
> > >
> > > +// On PowerPC, ucontext.h uses a pt_regs struct as an incomplete
> > > +// type. This type must be completed by including asm/ptrace.h.
> > > +#ifdef __PPC__
> > > +#include <asm/ptrace.h>
> > > +#endif
> > > +
> > >  #include "runtime.h"
> > >
> > >  #ifndef SA_RESTART
> >
> > --
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