semihosting: add --semihosting-config arg sub-argument

Add new "arg" sub-argument to the --semihosting-config allowing the user
to pass multiple input arguments separately. It is required for example
by UHI semihosting to construct argc and argv.

Also, update ARM semihosting to support new option (at the moment it is
the only target which cares about arguments).

If the semihosting is enabled and no semihosting args have been specified,
then fall back to -kernel/-append. The -append string is split on whitespace
before initializing semihosting.argv[1..n]; this is different from what
QEMU MIPS machines' pseudo-bootloaders do (i.e. argv[1] contains the whole
-append), but is more intuitive from UHI user's point of view and Linux
kernel just does not care as it concatenates argv[1..n] into single cmdline
string anyway.

Signed-off-by: Leon Alrae <leon.alrae@imgtec.com>
Message-id: 1434643256-16858-3-git-send-email-leon.alrae@imgtec.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

include/exec/semihost.h

@@ -36,9 +36,27 @@ static inline SemihostingTarget semihosting_get_target(void)
 {
     return SEMIHOSTING_TARGET_AUTO;
 }
+
+static inline const char *semihosting_get_arg(int i)
+{
+    return NULL;
+}
+
+static inline int semihosting_get_argc(void)
+{
+    return 0;
+}
+
+static inline const char *semihosting_get_cmdline(void)
+{
+    return NULL;
+}
 #else
 bool semihosting_enabled(void);
 SemihostingTarget semihosting_get_target(void);
+const char *semihosting_get_arg(int i);
+int semihosting_get_argc(void);
+const char *semihosting_get_cmdline(void);
 #endif
 
 #endif