semihosting: introduce CONFIG_SEMIHOSTING

There isn't much point building semihosting for platforms that don't
support it. Introduce a new symbol and enable it only for the softmmu
targets that need it.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

2 files changed, 67 insertions, 0 deletions

diff --git a/stubs/Makefile.objs b/stubs/Makefile.objs
index 73452ad265..9c7393b08c 100644
--- a/stubs/Makefile.objs
+++ b/stubs/Makefile.objs
@@ -40,3 +40,4 @@ stub-obj-y += pci-host-piix.o
 stub-obj-y += ram-block.o
 stub-obj-y += ramfb.o
 stub-obj-y += fw_cfg.o
+stub-obj-$(CONFIG_SOFTMMU) += semihost.o
diff --git a/stubs/semihost.c b/stubs/semihost.c
new file mode 100644
index 0000000000..1a4e88e532
--- /dev/null
+++ b/stubs/semihost.c
@@ -0,0 +1,66 @@
+/*
+ * Semihosting Stubs for SoftMMU
+ *
+ * Copyright (c) 2019 Linaro Ltd
+ *
+ * Stubs for SoftMMU targets that don't actually do semihosting.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/option.h"
+#include "qemu/error-report.h"
+#include "hw/semihosting/semihost.h"
+
+/* Empty config */
+QemuOptsList qemu_semihosting_config_opts = {
+    .name = "",
+    .head = QTAILQ_HEAD_INITIALIZER(qemu_semihosting_config_opts.head),
+    .desc = {
+        { /* end of list */ }
+    },
+};
+
+/* Queries to config status default to off */
+bool semihosting_enabled(void)
+{
+    return false;
+}
+
+SemihostingTarget semihosting_get_target(void)
+{
+    return SEMIHOSTING_TARGET_AUTO;
+}
+
+/*
+ * All the rest are empty subs. We could g_assert_not_reached() but
+ * that adds extra weight to the final binary. Waste not want not.
+ */
+void qemu_semihosting_enable(void)
+{
+}
+
+int qemu_semihosting_config_options(const char *optarg)
+{
+    return 1;
+}
+
+const char *semihosting_get_arg(int i)
+{
+    return NULL;
+}
+
+int semihosting_get_argc(void)
+{
+    return 0;
+}
+
+const char *semihosting_get_cmdline(void)
+{
+    return NULL;
+}
+
+void semihosting_arg_fallback(const char *file, const char *cmd)
+{
+}