target/arm: don't expose "ieee_half" via gdbstub

While support for parsing ieee_half in the XML description was added
to gdb in 2019 (a6d0f249) there is no easy way for the gdbstub to know
if the gdb end will understand it. Disable it for now and allow older
gdbs to successfully connect to the default -cpu max SVE enabled
QEMUs.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20200402143913.24005-1-alex.bennee@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
diff --git a/target/arm/gdbstub.c b/target/arm/gdbstub.c
index d9ef7d2..8efc535 100644
--- a/target/arm/gdbstub.c
+++ b/target/arm/gdbstub.c
@@ -192,7 +192,12 @@
     /* 16 bit */
     { "uint16", 16, 'h', 'u' },
     { "int16", 16, 'h', 's' },
-    { "ieee_half", 16, 'h', 'f' },
+    /*
+     * TODO: currently there is no reliable way of telling
+     * if the remote gdb actually understands ieee_half so
+     * we don't expose it in the target description for now.
+     * { "ieee_half", 16, 'h', 'f' },
+     */
     /* bytes */
     { "uint8", 8, 'b', 'u' },
     { "int8", 8, 'b', 's' },