gdb: fall back on sigpending + sigwait if sigtimedwait is not available

The macOS platform does not provide sigtimedwait, so we get:

      CXX    compile/compile.o
    In file included from /Users/smarchi/src/binutils-gdb/gdb/compile/compile.c:46:
    /Users/smarchi/src/binutils-gdb/gdb/../gdbsupport/scoped_ignore_signal.h:69:4: error: use of undeclared identifier 'sigtimedwait'
              sigtimedwait (&set, nullptr, &zero_timeout);
              ^

An alternative to sigtimedwait with a timeout of 0 is to use sigpending,
to first check which signals are pending, and then sigwait, to consume
them.  Since that's slightly more expensive (2 syscalls instead of 1),
keep using sigtimedwait for the platforms that provide it, and fall back
to sigpending + sigwait for the others.

gdbsupport/ChangeLog:

	* scoped_ignore_signal.h (struct scoped_ignore_signal)
	<~scoped_ignore_signal>: Use sigtimedwait if HAVE_SIGTIMEDWAIT
	is defined, else use sigpending + sigwait.

Change-Id: I2a72798337e81dd1bbd21214736a139dd350af87
Co-Authored-By: John Baldwin <jhb@FreeBSD.org>

diff --git a/gdbsupport/scoped_ignore_signal.h b/gdbsupport/scoped_ignore_signal.h
index a14c96779bf214d6a407dc2efcb8e3226c86347b..57dd4b6d4025654ee544353f934145620e2d610d 100644 (file)
--- a/gdbsupport/scoped_ignore_signal.h
+++ b/gdbsupport/scoped_ignore_signal.h
@@ -58,7 +58,6 @@ public:
     if (!m_was_blocked)
       {
        sigset_t set;
-       const timespec zero_timeout = {};
 
        sigemptyset (&set);
        sigaddset (&set, Sig);
@@ -66,7 +65,19 @@ public:
        /* If we got a pending Sig signal, consume it before
           unblocking.  */
        if (ConsumePending)
-         sigtimedwait (&set, nullptr, &zero_timeout);
+         {
+#ifdef HAVE_SIGTIMEDWAIT
+           const timespec zero_timeout = {};
+
+           sigtimedwait (&set, nullptr, &zero_timeout);
+#else
+           sigset_t pending;
+
+           sigpending (&pending);
+           if (sigismember (&pending, Sig))
+             sigwait (&set, nullptr);
+#endif
+         }
 
        sigprocmask (SIG_UNBLOCK, &set, nullptr);
       }