[PATCH v2 35/40] bsd-user/signal.c: implement do_sigreturn

[Warner Losh]

Implements the meat of a sigreturn(2) system call via do_sigreturn, and
helper reset_signal_mask. Fix the prototype of do_sigreturn in qemu.h
and remove do_rt_sigreturn since it's linux only.

Signed-off-by: Stacey Son <sson@FreeBSD.org>
Signed-off-by: Kyle Evans <kevans@freebsd.org>
Signed-off-by: Warner Losh <imp@bsdimp.com>

PENDING COMMENTS: from  Peter Maydell <peter.maydell@linaro.org>

do_sigreturn() itself shouldn't be setting the active signal
mask, at least if you follow the linux-user design. It just
sets the thread's signal_mask field in the TaskState by
calling set_sigmask(), and then on our way out in the
main cpu loop we'll call process_pending_signals() which
sets the real thread signal mask to that value. (This, together
with do_sigreturn() calling block_signals() before it starts
work, avoids some race conditions where a host signal is delivered
as soon as we unblock, I think.)
---
 bsd-user/signal-common.h |  2 +-
 bsd-user/signal.c        | 56 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 57 insertions(+), 1 deletion(-)

diff --git a/bsd-user/signal-common.h b/bsd-user/signal-common.h
index ee819266f54..786ec592d18 100644
--- a/bsd-user/signal-common.h
+++ b/bsd-user/signal-common.h
@@ -11,7 +11,7 @@
 
 long do_rt_sigreturn(CPUArchState *env);
 abi_long do_sigaltstack(abi_ulong uss_addr, abi_ulong uoss_addr, abi_ulong sp);
-long do_sigreturn(CPUArchState *env);
+long do_sigreturn(CPUArchState *env, abi_ulong addr);
 void force_sig_fault(int sig, int code, abi_ulong addr);
 int host_to_target_signal(int sig);
 void host_to_target_sigset(target_sigset_t *d, const sigset_t *s);
diff --git a/bsd-user/signal.c b/bsd-user/signal.c
index 9ec4354d232..05caf812ccb 100644
--- a/bsd-user/signal.c
+++ b/bsd-user/signal.c
@@ -626,6 +626,62 @@ static void setup_frame(int sig, int code, struct 
target_sigaction *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;
+    sigprocmask(SIG_SETMASK, &ts->signal_mask, NULL);
+
+    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;
-- 
2.33.1