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) > > 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. > > Cheers > ---Dave >
