Merge remote-tracking branch 'remotes/bsdimp/tags/bsd-user-arm-2022q1-pull-request' into staging

bsd-user: upstream signal implementation

Upstream the bsd-user fork signal implementation, for the most part.  This
series of commits represents nearly all of the infrastructure that surround
signals, except the actual system call glue (that was also reworked in the
fork and needs its own series). In addition, this adds the sigsegv and sigbus
code to arm. Even in the fork, we don't have good x86 signal implementation,
so there's little to upstream for that at the moment.

bsd-user's signal implementation is similar to linux-user's. The full context
can be found in the bsd-user's fork's 'blitz branch' at
https://github.com/qemu-bsd-user/qemu-bsd-user/tree/blitz which shows how these
are used to implement various system calls. Since this was built from
linux-user's stack stuff, evolved for BSD with the passage of a few years, it
no-doubt missed some bug fixes from linux-user (though nothing obvious stood out
in the quick comparison I made). After the first round of reviews, many of these
improvements have been incorporated.

Patchew history: https://patchew.org/QEMU/20220125012947.14974-1-imp@bsdimp.com/

# gpg: Signature made Mon 31 Jan 2022 19:55:51 GMT
# gpg:                using RSA key 2035F894B00AA3CF7CCDE1B76C1CD1287DB01100
# gpg: Good signature from "Warner Losh <wlosh@netflix.com>" [unknown]
# gpg:                 aka "Warner Losh <imp@bsdimp.com>" [unknown]
# gpg:                 aka "Warner Losh <imp@freebsd.org>" [unknown]
# gpg:                 aka "Warner Losh <imp@village.org>" [unknown]
# gpg:                 aka "Warner Losh <wlosh@bsdimp.com>" [unknown]
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# Primary key fingerprint: 2035 F894 B00A A3CF 7CCD  E1B7 6C1C D128 7DB0 1100

* remotes/bsdimp/tags/bsd-user-arm-2022q1-pull-request: (40 commits)
  bsd-user/freebsd/target_os_ucontext.h: Prefer env as arg name for CPUArchState args
  bsd-user: Rename arg name for target_cpu_reset to env
  MAINTAINERS: Add tests/vm/*bsd to the list to get reviews on
  bsd-user/signal.c: do_sigaltstack
  bsd-user/signal.c: implement do_sigaction
  bsd-user/signal.c: implement do_sigreturn
  bsd-user/signal.c: process_pending_signals
  bsd-user/signal.c: tswap_siginfo
  bsd-user/signal.c: handle_pending_signal
  bsd-user/signal.c: setup_frame
  bsd-user/signal.c: sigset manipulation routines.
  bsd-user/signal.c: Fill in queue_signal
  bsd-user/signal.c: Implement dump_core_and_abort
  bsd-user/strace.c: print_taken_signal
  bsd-user/signal.c: Implement host_signal_handler
  bsd-user/signal.c: Implement rewind_if_in_safe_syscall
  bsd-user/signal.c: host_to_target_siginfo_noswap
  bsd-user: Add trace events for bsd-user
  bsd-user: Add host signals to the build
  bsd-user/host/x86_64/host-signal.h: Implement host_signal_*
  ...

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 997 insertions, 11 deletions

diff --git a/bsd-user/signal.c b/bsd-user/signal.c
index 05b277c642..ad22ba9d90 100644
--- a/bsd-user/signal.c
+++ b/bsd-user/signal.c
@@ -2,6 +2,7 @@
  *  Emulation of BSD signals
  *
  *  Copyright (c) 2003 - 2008 Fabrice Bellard
+ *  Copyright (c) 2013 Stacey Son
  *
  *  This program is free software; you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
@@ -19,41 +20,1026 @@
 
 #include "qemu/osdep.h"
 #include "qemu.h"
+#include "signal-common.h"
+#include "trace.h"
+#include "hw/core/tcg-cpu-ops.h"
+#include "host-signal.h"
+
+static struct target_sigaction sigact_table[TARGET_NSIG];
+static void host_signal_handler(int host_sig, siginfo_t *info, void *puc);
+static void target_to_host_sigset_internal(sigset_t *d,
+        const target_sigset_t *s);
+
+static inline int on_sig_stack(TaskState *ts, unsigned long sp)
+{
+    return sp - ts->sigaltstack_used.ss_sp < ts->sigaltstack_used.ss_size;
+}
+
+static inline int sas_ss_flags(TaskState *ts, unsigned long sp)
+{
+    return ts->sigaltstack_used.ss_size == 0 ? SS_DISABLE :
+        on_sig_stack(ts, sp) ? SS_ONSTACK : 0;
+}
+
+/*
+ * The BSD ABIs use the same singal numbers across all the CPU architectures, so
+ * (unlike Linux) these functions are just the identity mapping. This might not
+ * be true for XyzBSD running on AbcBSD, which doesn't currently work.
+ */
+int host_to_target_signal(int sig)
+{
+    return sig;
+}
+
+int target_to_host_signal(int sig)
+{
+    return sig;
+}
+
+static inline void target_sigemptyset(target_sigset_t *set)
+{
+    memset(set, 0, sizeof(*set));
+}
+
+static inline void target_sigaddset(target_sigset_t *set, int signum)
+{
+    signum--;
+    uint32_t mask = (uint32_t)1 << (signum % TARGET_NSIG_BPW);
+    set->__bits[signum / TARGET_NSIG_BPW] |= mask;
+}
+
+static inline int target_sigismember(const target_sigset_t *set, int signum)
+{
+    signum--;
+    abi_ulong mask = (abi_ulong)1 << (signum % TARGET_NSIG_BPW);
+    return (set->__bits[signum / TARGET_NSIG_BPW] & mask) != 0;
+}
+
+/* Adjust the signal context to rewind out of safe-syscall if we're in it */
+static inline void rewind_if_in_safe_syscall(void *puc)
+{
+    ucontext_t *uc = (ucontext_t *)puc;
+    uintptr_t pcreg = host_signal_pc(uc);
+
+    if (pcreg > (uintptr_t)safe_syscall_start
+        && pcreg < (uintptr_t)safe_syscall_end) {
+        host_signal_set_pc(uc, (uintptr_t)safe_syscall_start);
+    }
+}
 
 /*
- * Stubbed out routines until we merge signal support from bsd-user
- * fork.
+ * Note: The following take advantage of the BSD signal property that all
+ * signals are available on all architectures.
  */
+static void host_to_target_sigset_internal(target_sigset_t *d,
+        const sigset_t *s)
+{
+    int i;
+
+    target_sigemptyset(d);
+    for (i = 1; i <= NSIG; i++) {
+        if (sigismember(s, i)) {
+            target_sigaddset(d, host_to_target_signal(i));
+        }
+    }
+}
+
+void host_to_target_sigset(target_sigset_t *d, const sigset_t *s)
+{
+    target_sigset_t d1;
+    int i;
+
+    host_to_target_sigset_internal(&d1, s);
+    for (i = 0; i < _SIG_WORDS; i++) {
+        d->__bits[i] = tswap32(d1.__bits[i]);
+    }
+}
+
+static void target_to_host_sigset_internal(sigset_t *d,
+        const target_sigset_t *s)
+{
+    int i;
+
+    sigemptyset(d);
+    for (i = 1; i <= TARGET_NSIG; i++) {
+        if (target_sigismember(s, i)) {
+            sigaddset(d, target_to_host_signal(i));
+        }
+    }
+}
+
+void target_to_host_sigset(sigset_t *d, const target_sigset_t *s)
+{
+    target_sigset_t s1;
+    int i;
+
+    for (i = 0; i < TARGET_NSIG_WORDS; i++) {
+        s1.__bits[i] = tswap32(s->__bits[i]);
+    }
+    target_to_host_sigset_internal(d, &s1);
+}
+
+static bool has_trapno(int tsig)
+{
+    return tsig == TARGET_SIGILL ||
+        tsig == TARGET_SIGFPE ||
+        tsig == TARGET_SIGSEGV ||
+        tsig == TARGET_SIGBUS ||
+        tsig == TARGET_SIGTRAP;
+}
+
+/* Siginfo conversion. */
+
+/*
+ * Populate tinfo w/o swapping based on guessing which fields are valid.
+ */
+static inline void host_to_target_siginfo_noswap(target_siginfo_t *tinfo,
+        const siginfo_t *info)
+{
+    int sig = host_to_target_signal(info->si_signo);
+    int si_code = info->si_code;
+    int si_type;
+
+    /*
+     * Make sure we that the variable portion of the target siginfo is zeroed
+     * out so we don't leak anything into that.
+     */
+    memset(&tinfo->_reason, 0, sizeof(tinfo->_reason));
+
+    /*
+     * This is awkward, because we have to use a combination of the si_code and
+     * si_signo to figure out which of the union's members are valid.o We
+     * therefore make our best guess.
+     *
+     * Once we have made our guess, we record it in the top 16 bits of
+     * the si_code, so that tswap_siginfo() later can use it.
+     * tswap_siginfo() will strip these top bits out before writing
+     * si_code to the guest (sign-extending the lower bits).
+     */
+    tinfo->si_signo = sig;
+    tinfo->si_errno = info->si_errno;
+    tinfo->si_code = info->si_code;
+    tinfo->si_pid = info->si_pid;
+    tinfo->si_uid = info->si_uid;
+    tinfo->si_status = info->si_status;
+    tinfo->si_addr = (abi_ulong)(unsigned long)info->si_addr;
+    /*
+     * si_value is opaque to kernel. On all FreeBSD platforms,
+     * sizeof(sival_ptr) >= sizeof(sival_int) so the following
+     * always will copy the larger element.
+     */
+    tinfo->si_value.sival_ptr =
+        (abi_ulong)(unsigned long)info->si_value.sival_ptr;
+
+    switch (si_code) {
+        /*
+         * All the SI_xxx codes that are defined here are global to
+         * all the signals (they have values that none of the other,
+         * more specific signal info will set).
+         */
+    case SI_USER:
+    case SI_LWP:
+    case SI_KERNEL:
+    case SI_QUEUE:
+    case SI_ASYNCIO:
+        /*
+         * Only the fixed parts are valid (though FreeBSD doesn't always
+         * set all the fields to non-zero values.
+         */
+        si_type = QEMU_SI_NOINFO;
+        break;
+    case SI_TIMER:
+        tinfo->_reason._timer._timerid = info->_reason._timer._timerid;
+        tinfo->_reason._timer._overrun = info->_reason._timer._overrun;
+        si_type = QEMU_SI_TIMER;
+        break;
+    case SI_MESGQ:
+        tinfo->_reason._mesgq._mqd = info->_reason._mesgq._mqd;
+        si_type = QEMU_SI_MESGQ;
+        break;
+    default:
+        /*
+         * We have to go based on the signal number now to figure out
+         * what's valid.
+         */
+        if (has_trapno(sig)) {
+            tinfo->_reason._fault._trapno = info->_reason._fault._trapno;
+            si_type = QEMU_SI_FAULT;
+        }
+#ifdef TARGET_SIGPOLL
+        /*
+         * FreeBSD never had SIGPOLL, but emulates it for Linux so there's
+         * a chance it may popup in the future.
+         */
+        if (sig == TARGET_SIGPOLL) {
+            tinfo->_reason._poll._band = info->_reason._poll._band;
+            si_type = QEMU_SI_POLL;
+        }
+#endif
+        /*
+         * Unsure that this can actually be generated, and our support for
+         * capsicum is somewhere between weak and non-existant, but if we get
+         * one, then we know what to save.
+         */
+        if (sig == TARGET_SIGTRAP) {
+            tinfo->_reason._capsicum._syscall =
+                info->_reason._capsicum._syscall;
+            si_type = QEMU_SI_CAPSICUM;
+        }
+        break;
+    }
+    tinfo->si_code = deposit32(si_code, 24, 8, si_type);
+}
+
+static void tswap_siginfo(target_siginfo_t *tinfo, const target_siginfo_t *info)
+{
+    int si_type = extract32(info->si_code, 24, 8);
+    int si_code = sextract32(info->si_code, 0, 24);
+
+    __put_user(info->si_signo, &tinfo->si_signo);
+    __put_user(info->si_errno, &tinfo->si_errno);
+    __put_user(si_code, &tinfo->si_code); /* Zero out si_type, it's internal */
+    __put_user(info->si_pid, &tinfo->si_pid);
+    __put_user(info->si_uid, &tinfo->si_uid);
+    __put_user(info->si_status, &tinfo->si_status);
+    __put_user(info->si_addr, &tinfo->si_addr);
+    /*
+     * Unswapped, because we passed it through mostly untouched.  si_value is
+     * opaque to the kernel, so we didn't bother with potentially wasting cycles
+     * to swap it into host byte order.
+     */
+    tinfo->si_value.sival_ptr = info->si_value.sival_ptr;
+
+    /*
+     * We can use our internal marker of which fields in the structure
+     * are valid, rather than duplicating the guesswork of
+     * host_to_target_siginfo_noswap() here.
+     */
+    switch (si_type) {
+    case QEMU_SI_NOINFO:        /* No additional info */
+        break;
+    case QEMU_SI_FAULT:
+        __put_user(info->_reason._fault._trapno,
+                   &tinfo->_reason._fault._trapno);
+        break;
+    case QEMU_SI_TIMER:
+        __put_user(info->_reason._timer._timerid,
+                   &tinfo->_reason._timer._timerid);
+        __put_user(info->_reason._timer._overrun,
+                   &tinfo->_reason._timer._overrun);
+        break;
+    case QEMU_SI_MESGQ:
+        __put_user(info->_reason._mesgq._mqd, &tinfo->_reason._mesgq._mqd);
+        break;
+    case QEMU_SI_POLL:
+        /* Note: Not generated on FreeBSD */
+        __put_user(info->_reason._poll._band, &tinfo->_reason._poll._band);
+        break;
+    case QEMU_SI_CAPSICUM:
+        __put_user(info->_reason._capsicum._syscall,
+                   &tinfo->_reason._capsicum._syscall);
+        break;
+    default:
+        g_assert_not_reached();
+    }
+}
+
+int block_signals(void)
+{
+    TaskState *ts = (TaskState *)thread_cpu->opaque;
+    sigset_t set;
+
+    /*
+     * It's OK to block everything including SIGSEGV, because we won't run any
+     * further guest code before unblocking signals in
+     * process_pending_signals(). We depend on the FreeBSD behaivor here where
+     * this will only affect this thread's signal mask. We don't use
+     * pthread_sigmask which might seem more correct because that routine also
+     * does odd things with SIGCANCEL to implement pthread_cancel().
+     */
+    sigfillset(&set);
+    sigprocmask(SIG_SETMASK, &set, 0);
+
+    return qatomic_xchg(&ts->signal_pending, 1);
+}
+
+/* Returns 1 if given signal should dump core if not handled. */
+static int core_dump_signal(int sig)
+{
+    switch (sig) {
+    case TARGET_SIGABRT:
+    case TARGET_SIGFPE:
+    case TARGET_SIGILL:
+    case TARGET_SIGQUIT:
+    case TARGET_SIGSEGV:
+    case TARGET_SIGTRAP:
+    case TARGET_SIGBUS:
+        return 1;
+    default:
+        return 0;
+    }
+}
+
+/* Abort execution with signal. */
+static void QEMU_NORETURN dump_core_and_abort(int target_sig)
+{
+    CPUArchState *env = thread_cpu->env_ptr;
+    CPUState *cpu = env_cpu(env);
+    TaskState *ts = cpu->opaque;
+    int core_dumped = 0;
+    int host_sig;
+    struct sigaction act;
+
+    host_sig = target_to_host_signal(target_sig);
+    gdb_signalled(env, target_sig);
+
+    /* Dump core if supported by target binary format */
+    if (core_dump_signal(target_sig) && (ts->bprm->core_dump != NULL)) {
+        stop_all_tasks();
+        core_dumped =
+            ((*ts->bprm->core_dump)(target_sig, env) == 0);
+    }
+    if (core_dumped) {
+        struct rlimit nodump;
+
+        /*
+         * We already dumped the core of target process, we don't want
+         * a coredump of qemu itself.
+         */
+         getrlimit(RLIMIT_CORE, &nodump);
+         nodump.rlim_cur = 0;
+         setrlimit(RLIMIT_CORE, &nodump);
+         (void) fprintf(stderr, "qemu: uncaught target signal %d (%s) "
+             "- %s\n", target_sig, strsignal(host_sig), "core dumped");
+    }
+
+    /*
+     * The proper exit code for dying from an uncaught signal is
+     * -<signal>.  The kernel doesn't allow exit() or _exit() to pass
+     * a negative value.  To get the proper exit code we need to
+     * actually die from an uncaught signal.  Here the default signal
+     * handler is installed, we send ourself a signal and we wait for
+     * it to arrive.
+     */
+    memset(&act, 0, sizeof(act));
+    sigfillset(&act.sa_mask);
+    act.sa_handler = SIG_DFL;
+    sigaction(host_sig, &act, NULL);
+
+    kill(getpid(), host_sig);
+
+    /*
+     * Make sure the signal isn't masked (just reuse the mask inside
+     * of act).
+     */
+    sigdelset(&act.sa_mask, host_sig);
+    sigsuspend(&act.sa_mask);
+
+    /* unreachable */
+    abort();
+}
 
 /*
  * Queue a signal so that it will be send to the virtual CPU as soon as
  * possible.
  */
-void queue_signal(CPUArchState *env, int sig, target_siginfo_t *info)
+void queue_signal(CPUArchState *env, int sig, int si_type,
+                  target_siginfo_t *info)
 {
-    qemu_log_mask(LOG_UNIMP, "No signal queueing, dropping signal %d\n", sig);
+    CPUState *cpu = env_cpu(env);
+    TaskState *ts = cpu->opaque;
+
+    trace_user_queue_signal(env, sig);
+
+    info->si_code = deposit32(info->si_code, 24, 8, si_type);
+
+    ts->sync_signal.info = *info;
+    ts->sync_signal.pending = sig;
+    /* Signal that a new signal is pending. */
+    qatomic_set(&ts->signal_pending, 1);
+    return;
+}
+
+static int fatal_signal(int sig)
+{
+
+    switch (sig) {
+    case TARGET_SIGCHLD:
+    case TARGET_SIGURG:
+    case TARGET_SIGWINCH:
+    case TARGET_SIGINFO:
+        /* Ignored by default. */
+        return 0;
+    case TARGET_SIGCONT:
+    case TARGET_SIGSTOP:
+    case TARGET_SIGTSTP:
+    case TARGET_SIGTTIN:
+    case TARGET_SIGTTOU:
+        /* Job control signals.  */
+        return 0;
+    default:
+        return 1;
+    }
+}
+
+/*
+ * Force a synchronously taken QEMU_SI_FAULT signal. For QEMU the
+ * 'force' part is handled in process_pending_signals().
+ */
+void force_sig_fault(int sig, int code, abi_ulong addr)
+{
+    CPUState *cpu = thread_cpu;
+    CPUArchState *env = cpu->env_ptr;
+    target_siginfo_t info = {};
+
+    info.si_signo = sig;
+    info.si_errno = 0;
+    info.si_code = code;
+    info.si_addr = addr;
+    queue_signal(env, sig, QEMU_SI_FAULT, &info);
+}
+
+static void host_signal_handler(int host_sig, siginfo_t *info, void *puc)
+{
+    CPUArchState *env = thread_cpu->env_ptr;
+    CPUState *cpu = env_cpu(env);
+    TaskState *ts = cpu->opaque;
+    target_siginfo_t tinfo;
+    ucontext_t *uc = puc;
+    struct emulated_sigtable *k;
+    int guest_sig;
+    uintptr_t pc = 0;
+    bool sync_sig = false;
+
+    /*
+     * Non-spoofed SIGSEGV and SIGBUS are synchronous, and need special
+     * handling wrt signal blocking and unwinding.
+     */
+    if ((host_sig == SIGSEGV || host_sig == SIGBUS) && info->si_code > 0) {
+        MMUAccessType access_type;
+        uintptr_t host_addr;
+        abi_ptr guest_addr;
+        bool is_write;
+
+        host_addr = (uintptr_t)info->si_addr;
+
+        /*
+         * Convert forcefully to guest address space: addresses outside
+         * reserved_va are still valid to report via SEGV_MAPERR.
+         */
+        guest_addr = h2g_nocheck(host_addr);
+
+        pc = host_signal_pc(uc);
+        is_write = host_signal_write(info, uc);
+        access_type = adjust_signal_pc(&pc, is_write);
+
+        if (host_sig == SIGSEGV) {
+            bool maperr = true;
+
+            if (info->si_code == SEGV_ACCERR && h2g_valid(host_addr)) {
+                /* If this was a write to a TB protected page, restart. */
+                if (is_write &&
+                    handle_sigsegv_accerr_write(cpu, &uc->uc_sigmask,
+                                                pc, guest_addr)) {
+                    return;
+                }
+
+                /*
+                 * With reserved_va, the whole address space is PROT_NONE,
+                 * which means that we may get ACCERR when we want MAPERR.
+                 */
+                if (page_get_flags(guest_addr) & PAGE_VALID) {
+                    maperr = false;
+                } else {
+                    info->si_code = SEGV_MAPERR;
+                }
+            }
+
+            sigprocmask(SIG_SETMASK, &uc->uc_sigmask, NULL);
+            cpu_loop_exit_sigsegv(cpu, guest_addr, access_type, maperr, pc);
+        } else {
+            sigprocmask(SIG_SETMASK, &uc->uc_sigmask, NULL);
+            if (info->si_code == BUS_ADRALN) {
+                cpu_loop_exit_sigbus(cpu, guest_addr, access_type, pc);
+            }
+        }
+
+        sync_sig = true;
+    }
+
+    /* Get the target signal number. */
+    guest_sig = host_to_target_signal(host_sig);
+    if (guest_sig < 1 || guest_sig > TARGET_NSIG) {
+        return;
+    }
+    trace_user_host_signal(cpu, host_sig, guest_sig);
+
+    host_to_target_siginfo_noswap(&tinfo, info);
+
+    k = &ts->sigtab[guest_sig - 1];
+    k->info = tinfo;
+    k->pending = guest_sig;
+    ts->signal_pending = 1;
+
+    /*
+     * For synchronous signals, unwind the cpu state to the faulting
+     * insn and then exit back to the main loop so that the signal
+     * is delivered immediately.
+     */
+    if (sync_sig) {
+        cpu->exception_index = EXCP_INTERRUPT;
+        cpu_loop_exit_restore(cpu, pc);
+    }
+
+    rewind_if_in_safe_syscall(puc);
+
+    /*
+     * Block host signals until target signal handler entered. We
+     * can't block SIGSEGV or SIGBUS while we're executing guest
+     * code in case the guest code provokes one in the window between
+     * now and it getting out to the main loop. Signals will be
+     * unblocked again in process_pending_signals().
+     */
+    sigfillset(&uc->uc_sigmask);
+    sigdelset(&uc->uc_sigmask, SIGSEGV);
+    sigdelset(&uc->uc_sigmask, SIGBUS);
+
+    /* Interrupt the virtual CPU as soon as possible. */
+    cpu_exit(thread_cpu);
+}
+
+/* do_sigaltstack() returns target values and errnos. */
+/* compare to kern/kern_sig.c sys_sigaltstack() and kern_sigaltstack() */
+abi_long do_sigaltstack(abi_ulong uss_addr, abi_ulong uoss_addr, abi_ulong sp)
+{
+    TaskState *ts = (TaskState *)thread_cpu->opaque;
+    int ret;
+    target_stack_t oss;
+
+    if (uoss_addr) {
+        /* Save current signal stack params */
+        oss.ss_sp = tswapl(ts->sigaltstack_used.ss_sp);
+        oss.ss_size = tswapl(ts->sigaltstack_used.ss_size);
+        oss.ss_flags = tswapl(sas_ss_flags(ts, sp));
+    }
+
+    if (uss_addr) {
+        target_stack_t *uss;
+        target_stack_t ss;
+        size_t minstacksize = TARGET_MINSIGSTKSZ;
+
+        ret = -TARGET_EFAULT;
+        if (!lock_user_struct(VERIFY_READ, uss, uss_addr, 1)) {
+            goto out;
+        }
+        __get_user(ss.ss_sp, &uss->ss_sp);
+        __get_user(ss.ss_size, &uss->ss_size);
+        __get_user(ss.ss_flags, &uss->ss_flags);
+        unlock_user_struct(uss, uss_addr, 0);
+
+        ret = -TARGET_EPERM;
+        if (on_sig_stack(ts, sp)) {
+            goto out;
+        }
+
+        ret = -TARGET_EINVAL;
+        if (ss.ss_flags != TARGET_SS_DISABLE
+            && ss.ss_flags != TARGET_SS_ONSTACK
+            && ss.ss_flags != 0) {
+            goto out;
+        }
+
+        if (ss.ss_flags == TARGET_SS_DISABLE) {
+            ss.ss_size = 0;
+            ss.ss_sp = 0;
+        } else {
+            ret = -TARGET_ENOMEM;
+            if (ss.ss_size < minstacksize) {
+                goto out;
+            }
+        }
+
+        ts->sigaltstack_used.ss_sp = ss.ss_sp;
+        ts->sigaltstack_used.ss_size = ss.ss_size;
+    }
+
+    if (uoss_addr) {
+        ret = -TARGET_EFAULT;
+        if (copy_to_user(uoss_addr, &oss, sizeof(oss))) {
+            goto out;
+        }
+    }
+
+    ret = 0;
+out:
+    return ret;
+}
+
+/* do_sigaction() return host values and errnos */
+int do_sigaction(int sig, const struct target_sigaction *act,
+        struct target_sigaction *oact)
+{
+    struct target_sigaction *k;
+    struct sigaction act1;
+    int host_sig;
+    int ret = 0;
+
+    if (sig < 1 || sig > TARGET_NSIG) {
+        return -TARGET_EINVAL;
+    }
+
+    if ((sig == TARGET_SIGKILL || sig == TARGET_SIGSTOP) &&
+        act != NULL && act->_sa_handler != TARGET_SIG_DFL) {
+        return -TARGET_EINVAL;
+    }
+
+    if (block_signals()) {
+        return -TARGET_ERESTART;
+    }
+
+    k = &sigact_table[sig - 1];
+    if (oact) {
+        oact->_sa_handler = tswapal(k->_sa_handler);
+        oact->sa_flags = tswap32(k->sa_flags);
+        oact->sa_mask = k->sa_mask;
+    }
+    if (act) {
+        k->_sa_handler = tswapal(act->_sa_handler);
+        k->sa_flags = tswap32(act->sa_flags);
+        k->sa_mask = act->sa_mask;
+
+        /* Update the host signal state. */
+        host_sig = target_to_host_signal(sig);
+        if (host_sig != SIGSEGV && host_sig != SIGBUS) {
+            memset(&act1, 0, sizeof(struct sigaction));
+            sigfillset(&act1.sa_mask);
+            act1.sa_flags = SA_SIGINFO;
+            if (k->sa_flags & TARGET_SA_RESTART) {
+                act1.sa_flags |= SA_RESTART;
+            }
+            /*
+             *  Note: It is important to update the host kernel signal mask to
+             *  avoid getting unexpected interrupted system calls.
+             */
+            if (k->_sa_handler == TARGET_SIG_IGN) {
+                act1.sa_sigaction = (void *)SIG_IGN;
+            } else if (k->_sa_handler == TARGET_SIG_DFL) {
+                if (fatal_signal(sig)) {
+                    act1.sa_sigaction = host_signal_handler;
+                } else {
+                    act1.sa_sigaction = (void *)SIG_DFL;
+                }
+            } else {
+                act1.sa_sigaction = host_signal_handler;
+            }
+            ret = sigaction(host_sig, &act1, NULL);
+        }
+    }
+    return ret;
+}
+
+static inline abi_ulong get_sigframe(struct target_sigaction *ka,
+        CPUArchState *env, size_t frame_size)
+{
+    TaskState *ts = (TaskState *)thread_cpu->opaque;
+    abi_ulong sp;
+
+    /* Use default user stack */
+    sp = get_sp_from_cpustate(env);
+
+    if ((ka->sa_flags & TARGET_SA_ONSTACK) && sas_ss_flags(ts, sp) == 0) {
+        sp = ts->sigaltstack_used.ss_sp + ts->sigaltstack_used.ss_size;
+    }
+
+/* TODO: make this a target_arch function / define */
+#if defined(TARGET_ARM)
+    return (sp - frame_size) & ~7;
+#elif defined(TARGET_AARCH64)
+    return (sp - frame_size) & ~15;
+#else
+    return sp - frame_size;
+#endif
+}
+
+/* compare to $M/$M/exec_machdep.c sendsig and sys/kern/kern_sig.c sigexit */
+
+static void setup_frame(int sig, int code, struct target_sigaction *ka,
+    target_sigset_t *set, target_siginfo_t *tinfo, CPUArchState *env)
+{
+    struct target_sigframe *frame;
+    abi_ulong frame_addr;
+    int i;
+
+    frame_addr = get_sigframe(ka, env, sizeof(*frame));
+    trace_user_setup_frame(env, frame_addr);
+    if (!lock_user_struct(VERIFY_WRITE, frame, frame_addr, 0)) {
+        unlock_user_struct(frame, frame_addr, 1);
+        dump_core_and_abort(TARGET_SIGILL);
+        return;
+    }
+
+    memset(frame, 0, sizeof(*frame));
+    setup_sigframe_arch(env, frame_addr, frame, 0);
+
+    for (i = 0; i < TARGET_NSIG_WORDS; i++) {
+        __put_user(set->__bits[i], &frame->sf_uc.uc_sigmask.__bits[i]);
+    }
+
+    if (tinfo) {
+        frame->sf_si.si_signo = tinfo->si_signo;
+        frame->sf_si.si_errno = tinfo->si_errno;
+        frame->sf_si.si_code = tinfo->si_code;
+        frame->sf_si.si_pid = tinfo->si_pid;
+        frame->sf_si.si_uid = tinfo->si_uid;
+        frame->sf_si.si_status = tinfo->si_status;
+        frame->sf_si.si_addr = tinfo->si_addr;
+        /* see host_to_target_siginfo_noswap() for more details */
+        frame->sf_si.si_value.sival_ptr = tinfo->si_value.sival_ptr;
+        /*
+         * At this point, whatever is in the _reason union is complete
+         * and in target order, so just copy the whole thing over, even
+         * if it's too large for this specific signal.
+         * host_to_target_siginfo_noswap() and tswap_siginfo() have ensured
+         * that's so.
+         */
+        memcpy(&frame->sf_si._reason, &tinfo->_reason,
+               sizeof(tinfo->_reason));
+    }
+
+    set_sigtramp_args(env, sig, frame, frame_addr, ka);
+
+    unlock_user_struct(frame, frame_addr, 1);
+}
+
+static int reset_signal_mask(target_ucontext_t *ucontext)
+{
+    int i;
+    sigset_t blocked;
+    target_sigset_t target_set;
+    TaskState *ts = (TaskState *)thread_cpu->opaque;
+
+    for (i = 0; i < TARGET_NSIG_WORDS; i++) {
+        if (__get_user(target_set.__bits[i],
+                    &ucontext->uc_sigmask.__bits[i])) {
+            return -TARGET_EFAULT;
+        }
+    }
+    target_to_host_sigset_internal(&blocked, &target_set);
+    ts->signal_mask = blocked;
+
+    return 0;
+}
+
+/* See sys/$M/$M/exec_machdep.c sigreturn() */
+long do_sigreturn(CPUArchState *env, abi_ulong addr)
+{
+    long ret;
+    abi_ulong target_ucontext;
+    target_ucontext_t *ucontext = NULL;
+
+    /* Get the target ucontext address from the stack frame */
+    ret = get_ucontext_sigreturn(env, addr, &target_ucontext);
+    if (is_error(ret)) {
+        return ret;
+    }
+    trace_user_do_sigreturn(env, addr);
+    if (!lock_user_struct(VERIFY_READ, ucontext, target_ucontext, 0)) {
+        goto badframe;
+    }
+
+    /* Set the register state back to before the signal. */
+    if (set_mcontext(env, &ucontext->uc_mcontext, 1)) {
+        goto badframe;
+    }
+
+    /* And reset the signal mask. */
+    if (reset_signal_mask(ucontext)) {
+        goto badframe;
+    }
+
+    unlock_user_struct(ucontext, target_ucontext, 0);
+    return -TARGET_EJUSTRETURN;
+
+badframe:
+    if (ucontext != NULL) {
+        unlock_user_struct(ucontext, target_ucontext, 0);
+    }
+    return -TARGET_EFAULT;
 }
 
 void signal_init(void)
 {
+    TaskState *ts = (TaskState *)thread_cpu->opaque;
+    struct sigaction act;
+    struct sigaction oact;
+    int i;
+    int host_sig;
+
+    /* Set the signal mask from the host mask. */
+    sigprocmask(0, 0, &ts->signal_mask);
+
+    sigfillset(&act.sa_mask);
+    act.sa_sigaction = host_signal_handler;
+    act.sa_flags = SA_SIGINFO;
+
+    for (i = 1; i <= TARGET_NSIG; i++) {
+#ifdef CONFIG_GPROF
+        if (i == TARGET_SIGPROF) {
+            continue;
+        }
+#endif
+        host_sig = target_to_host_signal(i);
+        sigaction(host_sig, NULL, &oact);
+        if (oact.sa_sigaction == (void *)SIG_IGN) {
+            sigact_table[i - 1]._sa_handler = TARGET_SIG_IGN;
+        } else if (oact.sa_sigaction == (void *)SIG_DFL) {
+            sigact_table[i - 1]._sa_handler = TARGET_SIG_DFL;
+        }
+        /*
+         * If there's already a handler installed then something has
+         * gone horribly wrong, so don't even try to handle that case.
+         * Install some handlers for our own use.  We need at least
+         * SIGSEGV and SIGBUS, to detect exceptions.  We can not just
+         * trap all signals because it affects syscall interrupt
+         * behavior.  But do trap all default-fatal signals.
+         */
+        if (fatal_signal(i)) {
+            sigaction(host_sig, &act, NULL);
+        }
+    }
 }
 
-void process_pending_signals(CPUArchState *cpu_env)
+static void handle_pending_signal(CPUArchState *env, int sig,
+                                  struct emulated_sigtable *k)
 {
+    CPUState *cpu = env_cpu(env);
+    TaskState *ts = cpu->opaque;
+    struct target_sigaction *sa;
+    int code;
+    sigset_t set;
+    abi_ulong handler;
+    target_siginfo_t tinfo;
+    target_sigset_t target_old_set;
+
+    trace_user_handle_signal(env, sig);
+
+    k->pending = 0;
+
+    sig = gdb_handlesig(cpu, sig);
+    if (!sig) {
+        sa = NULL;
+        handler = TARGET_SIG_IGN;
+    } else {
+        sa = &sigact_table[sig - 1];
+        handler = sa->_sa_handler;
+    }
+
+    if (do_strace) {
+        print_taken_signal(sig, &k->info);
+    }
+
+    if (handler == TARGET_SIG_DFL) {
+        /*
+         * default handler : ignore some signal. The other are job
+         * control or fatal.
+         */
+        if (sig == TARGET_SIGTSTP || sig == TARGET_SIGTTIN ||
+            sig == TARGET_SIGTTOU) {
+            kill(getpid(), SIGSTOP);
+        } else if (sig != TARGET_SIGCHLD && sig != TARGET_SIGURG &&
+                   sig != TARGET_SIGINFO && sig != TARGET_SIGWINCH &&
+                   sig != TARGET_SIGCONT) {
+            dump_core_and_abort(sig);
+        }
+    } else if (handler == TARGET_SIG_IGN) {
+        /* ignore sig */
+    } else if (handler == TARGET_SIG_ERR) {
+        dump_core_and_abort(sig);
+    } else {
+        /* compute the blocked signals during the handler execution */
+        sigset_t *blocked_set;
+
+        target_to_host_sigset(&set, &sa->sa_mask);
+        /*
+         * SA_NODEFER indicates that the current signal should not be
+         * blocked during the handler.
+         */
+        if (!(sa->sa_flags & TARGET_SA_NODEFER)) {
+            sigaddset(&set, target_to_host_signal(sig));
+        }
+
+        /*
+         * Save the previous blocked signal state to restore it at the
+         * end of the signal execution (see do_sigreturn).
+         */
+        host_to_target_sigset_internal(&target_old_set, &ts->signal_mask);
+
+        blocked_set = ts->in_sigsuspend ?
+            &ts->sigsuspend_mask : &ts->signal_mask;
+        sigorset(&ts->signal_mask, blocked_set, &set);
+        ts->in_sigsuspend = false;
+        sigprocmask(SIG_SETMASK, &ts->signal_mask, NULL);
+
+        /* XXX VM86 on x86 ??? */
+
+        code = k->info.si_code; /* From host, so no si_type */
+        /* prepare the stack frame of the virtual CPU */
+        if (sa->sa_flags & TARGET_SA_SIGINFO) {
+            tswap_siginfo(&tinfo, &k->info);
+            setup_frame(sig, code, sa, &target_old_set, &tinfo, env);
+        } else {
+            setup_frame(sig, code, sa, &target_old_set, NULL, env);
+        }
+        if (sa->sa_flags & TARGET_SA_RESETHAND) {
+            sa->_sa_handler = TARGET_SIG_DFL;
+        }
+    }
+}
+
+void process_pending_signals(CPUArchState *env)
+{
+    CPUState *cpu = env_cpu(env);
+    int sig;
+    sigset_t *blocked_set, set;
+    struct emulated_sigtable *k;
+    TaskState *ts = cpu->opaque;
+
+    while (qatomic_read(&ts->signal_pending)) {
+        sigfillset(&set);
+        sigprocmask(SIG_SETMASK, &set, 0);
+
+    restart_scan:
+        sig = ts->sync_signal.pending;
+        if (sig) {
+            /*
+             * Synchronous signals are forced by the emulated CPU in some way.
+             * If they are set to ignore, restore the default handler (see
+             * sys/kern_sig.c trapsignal() and execsigs() for this behavior)
+             * though maybe this is done only when forcing exit for non SIGCHLD.
+             */
+            if (sigismember(&ts->signal_mask, target_to_host_signal(sig)) ||
+                sigact_table[sig - 1]._sa_handler == TARGET_SIG_IGN) {
+                sigdelset(&ts->signal_mask, target_to_host_signal(sig));
+                sigact_table[sig - 1]._sa_handler = TARGET_SIG_DFL;
+            }
+            handle_pending_signal(env, sig, &ts->sync_signal);
+        }
+
+        k = ts->sigtab;
+        for (sig = 1; sig <= TARGET_NSIG; sig++, k++) {
+            blocked_set = ts->in_sigsuspend ?
+                &ts->sigsuspend_mask : &ts->signal_mask;
+            if (k->pending &&
+                !sigismember(blocked_set, target_to_host_signal(sig))) {
+                handle_pending_signal(env, sig, k);
+                /*
+                 * Restart scan from the beginning, as handle_pending_signal
+                 * might have resulted in a new synchronous signal (eg SIGSEGV).
+                 */
+                goto restart_scan;
+            }
+        }
+
+        /*
+         * Unblock signals and check one more time. Unblocking signals may cause
+         * us to take another host signal, which will set signal_pending again.
+         */
+        qatomic_set(&ts->signal_pending, 0);
+        ts->in_sigsuspend = false;
+        set = ts->signal_mask;
+        sigdelset(&set, SIGSEGV);
+        sigdelset(&set, SIGBUS);
+        sigprocmask(SIG_SETMASK, &set, 0);
+    }
+    ts->in_sigsuspend = false;
 }
 
 void cpu_loop_exit_sigsegv(CPUState *cpu, target_ulong addr,
                            MMUAccessType access_type, bool maperr, uintptr_t ra)
 {
-    qemu_log_mask(LOG_UNIMP, "No signal support for SIGSEGV\n");
-    /* unreachable */
-    abort();
+    const struct TCGCPUOps *tcg_ops = CPU_GET_CLASS(cpu)->tcg_ops;
+
+    if (tcg_ops->record_sigsegv) {
+        tcg_ops->record_sigsegv(cpu, addr, access_type, maperr, ra);
+    }
+
+    force_sig_fault(TARGET_SIGSEGV,
+                    maperr ? TARGET_SEGV_MAPERR : TARGET_SEGV_ACCERR,
+                    addr);
+    cpu->exception_index = EXCP_INTERRUPT;
+    cpu_loop_exit_restore(cpu, ra);
 }
 
 void cpu_loop_exit_sigbus(CPUState *cpu, target_ulong addr,
                           MMUAccessType access_type, uintptr_t ra)
 {
-    qemu_log_mask(LOG_UNIMP, "No signal support for SIGBUS\n");
-    /* unreachable */
-    abort();
+    const struct TCGCPUOps *tcg_ops = CPU_GET_CLASS(cpu)->tcg_ops;
+
+    if (tcg_ops->record_sigbus) {
+        tcg_ops->record_sigbus(cpu, addr, access_type, ra);
+    }
+
+    force_sig_fault(TARGET_SIGBUS, TARGET_BUS_ADRALN, addr);
+    cpu->exception_index = EXCP_INTERRUPT;
+    cpu_loop_exit_restore(cpu, ra);
 }