libgo: include asm/ptrace.h for pt_regs definition on PowerPC

  From: Sören Tempel <soeren@soeren-tempel.net>

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(+)
  

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
  

On Jan 02 2022, soeren--- via Gcc-patches wrote:

> 	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;

Why does that use .regs instead of .uc_regs?
  

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
>
> --
> You received this message because you are subscribed to the Google Groups "gofrontend-dev" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to gofrontend-dev+unsubscribe@googlegroups.com.
> To view this discussion on the web visit https://groups.google.com/d/msgid/gofrontend-dev/2FICMX0ORZ6O1.3DYXRTDHNGXCN%408pit.net.
  

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
> >
> > --
> > You received this message because you are subscribed to the Google Groups "gofrontend-dev" group.
> > To unsubscribe from this group and stop receiving emails from it, send an email to gofrontend-dev+unsubscribe@googlegroups.com.
> > To view this discussion on the web visit https://groups.google.com/d/msgid/gofrontend-dev/2FICMX0ORZ6O1.3DYXRTDHNGXCN%408pit.net.
  

On Mon, Feb 21, 2022 at 09:25:43AM -0800, Ian Lance Taylor via Gcc-patches wrote:
> Note for gofrontend-dev: on gcc-patches only Andreas Schwab suggested
> using uc_regs instead of regs, which does look correct to me.

Yes, this is absolutely the correct fix. Having pt_regs appear at all
in code not using ptrace is a serious code smell.

The root of this problem is twofold: (1) ancient Linux (2.0.x?) had a
bad definition of powerpc32 ucontext_t that lacked any mcontext_t,
instead having a regs member pointing to the storage for the register
state (as pt_regs). This was ostensibly done for extensibility
reasons, but was non-POSIX-conforming and broken, and was later fixed.

And (2) glibc's definition of ucontext_t is also non-conforming,
making the uc_mcontext member have type anon-union rather than type
mcontext_t.

musl does not follow this but puts the uc_mcontext member in the place
later kernel ABI assigned to it after the kernel mistake was fixed.

Ideally you would access uc_mcontext.gregs[32] (32==NIP) and be done
with it, but this won't work on glibc because of (2). However musl
also supports the old uc_regs pointer (it's in the reserved namespace
anyway so not a conformance error), making it so uc_regs->gregs[32]
works on either.

Rich



> 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
> >
> > --
> > You received this message because you are subscribed to the Google Groups "gofrontend-dev" group.
> > To unsubscribe from this group and stop receiving emails from it, send an email to gofrontend-dev+unsubscribe@googlegroups.com.
> > To view this discussion on the web visit https://groups.google.com/d/msgid/gofrontend-dev/2FICMX0ORZ6O1.3DYXRTDHNGXCN%408pit.net.
  

On Sun, Mar 06, 2022 at 10:22:56AM -0500, Rich Felker wrote:
> On Mon, Feb 21, 2022 at 09:25:43AM -0800, Ian Lance Taylor via Gcc-patches wrote:
> > Note for gofrontend-dev: on gcc-patches only Andreas Schwab suggested
> > using uc_regs instead of regs, which does look correct to me.
> 
> Yes, this is absolutely the correct fix. Having pt_regs appear at all
> in code not using ptrace is a serious code smell.
> 
> The root of this problem is twofold: (1) ancient Linux (2.0.x?) had a
> bad definition of powerpc32 ucontext_t that lacked any mcontext_t,
> instead having a regs member pointing to the storage for the register
> state (as pt_regs). This was ostensibly done for extensibility
> reasons, but was non-POSIX-conforming and broken, and was later fixed.
> 
> And (2) glibc's definition of ucontext_t is also non-conforming,
> making the uc_mcontext member have type anon-union rather than type
> mcontext_t.
> 
> musl does not follow this but puts the uc_mcontext member in the place
> later kernel ABI assigned to it after the kernel mistake was fixed.
> 
> Ideally you would access uc_mcontext.gregs[32] (32==NIP) and be done
> with it, but this won't work on glibc because of (2). However musl
> also supports the old uc_regs pointer (it's in the reserved namespace
> anyway so not a conformance error), making it so uc_regs->gregs[32]
> works on either.

I mistakenly thought this was ppc32 because I wasn't remembering that
a lesser mess was still present on ppc64. The above applies to ppc32.
On ppc64 it would be uc_mcontext.gp_regs[32].

I'm not sure if the code is intended to also work on ppc32, but even
if that's not supported now, when fixing this it should probably
condition the use of gregs/gp_regs name on __WORDSIZE or whatever so
that, if anyone ever does try to add ppc32 support, they don't get
bogged down in this again and get it wrong again...

Rich



> > 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
> > >
> > > --
> > > You received this message because you are subscribed to the Google Groups "gofrontend-dev" group.
> > > To unsubscribe from this group and stop receiving emails from it, send an email to gofrontend-dev+unsubscribe@googlegroups.com.
> > > To view this discussion on the web visit https://groups.google.com/d/msgid/gofrontend-dev/2FICMX0ORZ6O1.3DYXRTDHNGXCN%408pit.net.