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 <soe...@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 <soe...@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 <soe...@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+unsubscr...@googlegroups.com. > > > To view this discussion on the web visit > > > https://groups.google.com/d/msgid/gofrontend-dev/2FICMX0ORZ6O1.3DYXRTDHNGXCN%408pit.net.
