[RFA] gdbserver crash if the_target->supports_z_point_type is NULL

[Joel Brobecker <brobecker@adacore.com>]

Hello,

When debugging on LynxOS targets (and probably on SPU targets as well),
inserting a breakpoint and resuming the program's execution causes
GDBserver to crash.

The crash occurs while handling the Z0 packet sent by GDB to insert
our breakpoint, because z_type_supported calls
the_target->supports_z_point_type without checking that it is not NULL
This patch fixes the issue by making z_type_supported return false if
the_target->supports_z_point_type is NULL.

gdb/gdbserver/ChangeLog:

        PR server/17023
        * mem-break.c (z_type_supported): Return zero if
        THE_TARGET->SUPPORTS_Z_POINT_TYPE is NULL.

Tested on ppx-lynx5. I haven't tested on GNU/Linux, but I feel
sufficiently confident since supports_z_point_type is defined there,
and I am eager to take a look at Windows next. But I can do it
if people think it would be best.  OK to push?

Thanks,
-- 
Joel

---
 gdb/gdbserver/mem-break.c |    1 +
 1 file changed, 1 insertion(+)

diff --git a/gdb/gdbserver/mem-break.c b/gdb/gdbserver/mem-break.c
index 71876f7..2ce3ab2 100644
--- a/gdb/gdbserver/mem-break.c
+++ b/gdb/gdbserver/mem-break.c
@@ -897,6 +897,7 @@ static int
 z_type_supported (char z_type)
 {
   return (z_type >= '0' && z_type <= '4'
+	  && the_target->supports_z_point_type != NULL
 	  && the_target->supports_z_point_type (z_type));
 }
 
-- 
1.7.9.5