[v2,17/40] bsd-user/signal.c: Implement signal_init()

Commit Message

Warner Losh Jan. 25, 2022, 1:29 a.m. UTC

Initialize the signal state for the emulator. Setup a set of sane
default signal handlers, mirroring the host's signals. For fatal signals
(those that exit by default), establish our own set of signal
handlers. Stub out the actual signal handler we use for the moment.

Signed-off-by: Stacey Son <[e-mail]>
Signed-off-by: Kyle Evans <[e-mail]>
Signed-off-by: Warner Losh <[e-mail]>
Reviewed-by: Peter Maydell <[e-mail]>
Reviewed-by: Richard Henderson <[e-mail]> XXX SIGPROF PENDING
---
 bsd-user/qemu.h   |  7 +++++
 bsd-user/signal.c | 67 +++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 74 insertions(+)

Patch

diff --git a/bsd-user/qemu.h b/bsd-user/qemu.h
index 99c37fc9942..49f01932a53 100644
--- a/bsd-user/qemu.h
+++ b/bsd-user/qemu.h
@@ -94,6 +94,13 @@  typedef struct TaskState {
      * from multiple threads.)
      */
     int signal_pending;
+    /*
+     * This thread's signal mask, as requested by the guest program.
+     * The actual signal mask of this thread may differ:
+     *  + we don't let SIGSEGV and SIGBUS be blocked while running guest code
+     *  + sometimes we block all signals to avoid races
+     */
+    sigset_t signal_mask;
 
     uint8_t stack[];
 } __attribute__((aligned(16))) TaskState;
diff --git a/bsd-user/signal.c b/bsd-user/signal.c
index 1313baec96a..3ef7cf5e23c 100644
--- a/bsd-user/signal.c
+++ b/bsd-user/signal.c
@@ -28,6 +28,9 @@ 
  * fork.
  */
 
+static struct target_sigaction sigact_table[TARGET_NSIG];
+static void host_signal_handler(int host_sig, siginfo_t *info, void *puc);
+
 /*
  * 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
@@ -52,6 +55,28 @@  void queue_signal(CPUArchState *env, int sig, target_siginfo_t *info)
     qemu_log_mask(LOG_UNIMP, "No signal queueing, dropping signal %d\n", sig);
 }
 
+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().
@@ -69,8 +94,50 @@  void force_sig_fault(int sig, int code, abi_ulong addr)
     queue_signal(env, sig, &info);
 }
 
+static void host_signal_handler(int host_sig, siginfo_t *info, void *puc)
+{
+}
+
 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)