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This change will be integrated but ignored (-ay) to the gg-epcore/union sources, so that they retain HopeNames. Copied from Perforce Change: 24911 ServerID: perforce.ravenbrook.com
137 lines
4.5 KiB
C
137 lines
4.5 KiB
C
/* impl.c.protfri3: PROTECTION FOR FREEBSD (INTEL 386)
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*
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* $Id$
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* Copyright (c) 2001 Ravenbrook Limited.
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*
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* SOURCES
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*
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* .source.i486: Intel486 Microprocessor Family Programmer's
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* Reference Manual
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*
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* .source.man: sigaction(2): FreeBSD System Calls Manual.
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*/
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#include "prmcfr.h"
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#ifndef MPS_OS_FR
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#error "protfri3.c is FreeBSD-specific, but MPS_OS_FR is not set"
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#endif
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#if !defined(MPS_ARCH_I3) && !defined(MPS_ARCH_I4)
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#error "protfri3.c is Intel-specific, but MPS_ARCH_I3 or MPS_ARCH_I4 is not set"
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#endif
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#ifndef PROTECTION
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#error "protfri3.c implements protection, but PROTECTION is not set"
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#endif
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#include <signal.h>
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#include <machine/trap.h>
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SRCID(protfri3, "$Id$");
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/* The previously-installed signal action, as returned by */
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/* sigaction(3). See ProtSetup. */
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static struct sigaction sigNext;
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/* sigHandle -- protection signal handler
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*
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* This is the signal handler installed by ProtSetup to deal with
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* protection faults. It is installed on the SIGBUS signal. It
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* decodes the protection fault details from the signal context and
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* passes them to ArenaAccess, which attempts to handle the fault and
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* remove its cause. If the fault is handled, then the handler
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* returns and execution resumes. If it isn't handled, then
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* sigHandle does its best to pass the signal on to the previously
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* installed signal handler (sigNext).
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*
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* .sigh.args: The sigaction manual page .source.man documents three
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* different handler prototypes: ANSI C sa_handler, traditional BSD
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* sa_handler, and POSIX SA_SIGINFO sa_sigaction. The ANSI C
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* prototype isn't powerful enough for us (can't get addresses), and
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* the manual page deprecates the BSD sa_handler in favour of the
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* POSIX SA_SIGINFO sa_sigaction. In that prototype, the arguments
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* are: signal number, pointer to signal info structure, pointer to
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* signal context structure.
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*
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* .sigh.context: We only know how to handle signals with code
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* BUS_PAGE_FAULT, where info->si_addr gives the fault address.
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*
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* .sigh.mode: The fault type (read/write) does not appear to be
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* available to the signal handler (see mail archive).
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*/
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static void sigHandle(int sig, siginfo_t *info, void *context) /* .sigh.args */
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{
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AVER(sig == SIGBUS);
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if(info->si_code == BUS_PAGE_FAULT) { /* .sigh.context */
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AccessSet mode;
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Addr base, limit;
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mode = AccessREAD | AccessWRITE; /* .sigh.mode */
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/* We assume that the access is for one word at the address. */
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base = (Addr)info->si_addr; /* .sigh.context */
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limit = AddrAdd(base, (Size)sizeof(Addr));
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/* Offer each protection structure the opportunity to handle the */
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/* exception. If it succeeds, then allow the mutator to continue. */
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if(ArenaAccess(base, mode, NULL))
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return;
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}
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/* The exception was not handled by any known protection structure, */
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/* so throw it to the previously installed handler. */
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/* @@@@ This is really weak. */
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/* Need to implement rest of the contract of sigaction */
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/* We might also want to set SA_RESETHAND in the flags and explicitly */
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/* reinstall the handler from withint itself so the SIG_DFL/SIG_IGN */
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/* case can work properly by just returning. */
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switch ((int)sigNext.sa_handler) {
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case (int)SIG_DFL:
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case (int)SIG_IGN:
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abort();
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NOTREACHED;
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break;
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default:
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if ((int)sigNext.sa_handler & SA_SIGINFO) {
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(*sigNext.sa_sigaction)(sig, info, context);
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} else {
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/* @@@@ what if the previous handler is BSD-style? */
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/* We don't have a struct sigcontext to pass to it.
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The second argument (the code) is just info->si_code
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but the third argument (the sigcontext) we would have to
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fake from the ucontext. We could do that. */
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(*sigNext.sa_handler)(sig);
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}
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break;
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}
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}
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/* ProtSetup -- global protection setup
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*
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* Under FreeBSD, the global setup involves installing a signal
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* handler on SIGBUS to catch and handle page faults (see
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* sigHandle). The previous handler is recorded so that it can be
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* reached from sigHandle if it fails to handle the fault.
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*
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* NOTE: There are problems with this approach:
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* 1. we can't honor the sa_flags for the previous handler,
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* 2. what if this thread is suspended just after calling signal(3)?
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* The sigNext variable will never be initialized! */
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void ProtSetup(void)
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{
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struct sigaction sa;
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int result;
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sa.sa_sigaction = sigHandle;
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sigemptyset(&sa.sa_mask);
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sa.sa_flags = SA_SIGINFO;
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result = sigaction(SIGBUS, &sa, &sigNext);
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AVER(result == 0);
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}
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