tests/tcg: add a dumb-as-bricks semihosting console test

We don't run this during check-tcg as we would need to check stuff is
echoed back. However we can still build the binary so people can test
it manually.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

tests/tcg/aarch64/Makefile.softmmu-target

@@ -31,7 +31,16 @@ LDFLAGS+=-static -nostdlib $(CRT_OBJS) $(MINILIB_OBJS) -lgcc
 memory: CFLAGS+=-DCHECK_UNALIGNED=1
 
 # Running
-QEMU_OPTS+=-M virt -cpu max -display none -semihosting-config enable=on,target=native,chardev=output -kernel
+QEMU_BASE_MACHINE=-M virt -cpu max -display none
+QEMU_OPTS+=$(QEMU_BASE_MACHINE) -semihosting-config enable=on,target=native,chardev=output -kernel
+
+# console test is manual only
+QEMU_SEMIHOST=-chardev stdio,mux=on,id=stdio0 -semihosting-config enable=on,chardev=stdio0 -mon chardev=stdio0,mode=readline
+run-semiconsole: QEMU_OPTS=$(QEMU_BASE_MACHINE) $(QEMU_SEMIHOST)  -kernel
+run-semiconsole: semiconsole
+	$(call skip-test, $<, "MANUAL ONLY")
+run-plugin-semiconsole-with-%: semiconsole
+	$(call skip-test, $<, "MANUAL ONLY")
 
 # Simple Record/Replay Test
 .PHONY: memory-record

tests/tcg/aarch64/system/semiconsole.c

@@ -0,0 +1,38 @@
+/*
+ * Semihosting Console Test
+ *
+ * Copyright (c) 2019 Linaro Ltd
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include <inttypes.h>
+#include <minilib.h>
+
+#define SYS_READC 0x7
+
+uintptr_t __semi_call(uintptr_t type, uintptr_t arg0)
+{
+    register uintptr_t t asm("x0") = type;
+    register uintptr_t a0 asm("x1") = arg0;
+    asm("hlt 0xf000"
+        : "=r" (t)
+        : "r" (t), "r" (a0));
+
+    return t;
+}
+
+int main(void)
+{
+    char c;
+
+    ml_printf("Semihosting Console Test\n");
+    ml_printf("hit X to exit:");
+
+    do {
+        c = __semi_call(SYS_READC, 0);
+        __sys_outc(c);
+    } while (c != 'X');
+
+    return 0;
+}