gdbstub: Clarify what gdb_handlesig() is doing

gdb_handlesig()'s behaviour is not entirely obvious at first
glance. Add a doc comment for it, and also add a comment
explaining why it's ok for gdb_do_syscallv() to ignore
gdb_handlesig()'s return value. (Coverity complains about
this: CID 1390850.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20180515181958.25837-1-peter.maydell@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

1 files changed, 6 insertions, 0 deletions

diff --git a/gdbstub.c b/gdbstub.c
index e4ece2f5bc..6081e719c5 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -1558,6 +1558,12 @@ void gdb_do_syscallv(gdb_syscall_complete_cb cb, const char *fmt, va_list va)
     *p = 0;
 #ifdef CONFIG_USER_ONLY
     put_packet(s, s->syscall_buf);
+    /* Return control to gdb for it to process the syscall request.
+     * Since the protocol requires that gdb hands control back to us
+     * using a "here are the results" F packet, we don't need to check
+     * gdb_handlesig's return value (which is the signal to deliver if
+     * execution was resumed via a continue packet).
+     */
     gdb_handlesig(s->c_cpu, 0);
 #else
     /* In this case wait to send the syscall packet until notification that