On Fri, Dec 14, 2018 at 07:00:07PM +0000, Szabolcs Nagy wrote: > On 14/12/2018 18:25, Dave Martin wrote: > > On Fri, Dec 14, 2018 at 06:13:33PM +0000, Szabolcs Nagy wrote: > >> On 11/12/2018 19:26, Dave Martin wrote: > >>> This patch refactors the UAPI header definitions for the Arm SVE > >>> extension to avoid multiple-definition problems when userspace mixes its > >>> own sigcontext.h definitions with the kernel's ptrace.h (which is > >>> apparently routine). > >>> > >>> A common backend header is created to hold common definitions, suitably > >>> namespaced, and with an appropriate header guard. > >>> > >>> See the commit message in patch 3 for further explanation of why this > >>> is needed. > >>> > >>> Because of the non-trivial header guard in the new sve_context.h, patch > >>> 1 adds support to headers_install.sh to munge #if defined(_UAPI_FOO) in > >>> a similar way to the current handling of #ifndef _UAPI_FOO. > >>> > >> > >> thanks for doing this. > >> > >> the patches fix the gdb build issue on musl libc with an > >> additional gdb patch: > >> https://sourceware.org/ml/gdb-patches/2018-12/msg00152.html > >> (in userspace i'd expect users relying on signal.h providing > >> whatever is in asm/sigcontext.h.) > >> > >> i think sve_context.h could be made to work with direct include, > >> even if that's not useful because there is no public api there. > >> (and then you dont need the first patch) > > > > My general view is that if you want the sigframe types userspace should > > usually include <ucontext.h> and refer to mcontext_t. > > > > ucontext.h does not expose the asm/sigcontext.h types in glibc, > but it is compatible with the inclusion of asm/sigcontext.h > (or signal.h). > > in musl ucontext.h includes signal.h and signal.h provides > the asm/sigcontext.h api with abi compatible definitions. > > > Because the prototype for sa_sigaction() specifies a void * for the > > ucontext argument, I've generally assumed that <signal.h> is not > > sufficient to get ucontext_t (or mcontext_t) (but maybe I'm too paranoid > > there). > > http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/signal.h.html > > "The <signal.h> header shall define the ucontext_t type as a structure > that shall include at least the following members: > ... > mcontext_t uc_mcontext A machine-specific representation of the saved > context." > > so signal.h must define ucontext_t but mcontext_t can be opaque. > (it is opaque with posix conform feature tests to avoid > namespace pollution, but with _GNU_SOURCE defined all > asm/sigcontext.h apis are there and mcontext_t matches > struct sigcontext)
I see. Sounds reasonable. > > > > Non-POSIX-flavoured software might include <asm/sigcontext.h> directly. > > In glibc/musl libc will that conflict with <signal.h>, or can the two > > coexist? > > if you compile e.g in standard conform mode then > i think signal.h and asm/sigcontext.h are compatible. So long as we don't break any existing usage (?) I guess this is fine. Cheers ---Dave
