Add the "-semihosting-config" option.

The usual semihosting behaviour is to process the system calls locally and
return; unfortuantelly the initial implementation dinamically changed the
target to GDB during debug sessions, which, for the usual arm-none-eabi-gdb,
is not implemented. The result was that during debug sessions the semihosting
calls were discarded.

This patch adds a configuration variable and an option to set it on the
command line:

    -semihosting-config [enable=on|off,]target=native|gdb|auto

This option enables semihosting and defines where the semihosting calls will
be addressed, to QEMU ('native') or to GDB ('gdb'). The default is auto, which
means 'gdb' during debug sessions and 'native' otherwise.

Signed-off-by: Liviu Ionescu <ilg@livius.net>
Message-id: 1416341957-9796-1-git-send-email-ilg@livius.net
[PMM: moved declaration and definition of semihosting_target to
 gdbstub.h and gdbstub.c to fix build failure on linux-user]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

4 files changed, 78 insertions, 3 deletions

diff --git a/gdbstub.c b/gdbstub.c
index 0faca56..e4a1a79 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -317,6 +317,8 @@ static GDBState *gdbserver_state;
 
 bool gdb_has_xml;
 
+int semihosting_target = SEMIHOSTING_TARGET_AUTO;
+
 #ifdef CONFIG_USER_ONLY
 /* XXX: This is not thread safe.  Do we care?  */
 static int gdbserver_fd = -1;
@@ -351,10 +353,19 @@ static enum {
     GDB_SYS_DISABLED,
 } gdb_syscall_mode;
 
-/* If gdb is connected when the first semihosting syscall occurs then use
-   remote gdb syscalls.  Otherwise use native file IO.  */
+/* Decide if either remote gdb syscalls or native file IO should be used. */
 int use_gdb_syscalls(void)
 {
+    if (semihosting_target == SEMIHOSTING_TARGET_NATIVE) {
+        /* -semihosting-config target=native */
+        return false;
+    } else if (semihosting_target == SEMIHOSTING_TARGET_GDB) {
+        /* -semihosting-config target=gdb */
+        return true;
+    }
+
+    /* -semihosting-config target=auto */
+    /* On the first call check if gdb is connected and remember. */
     if (gdb_syscall_mode == GDB_SYS_UNKNOWN) {
         gdb_syscall_mode = (gdbserver_state ? GDB_SYS_ENABLED
                                             : GDB_SYS_DISABLED);
diff --git a/include/exec/gdbstub.h b/include/exec/gdbstub.h
index a608a26..c633248 100644
--- a/include/exec/gdbstub.h
+++ b/include/exec/gdbstub.h
@@ -95,4 +95,10 @@ extern bool gdb_has_xml;
 /* in gdbstub-xml.c, generated by scripts/feature_to_c.sh */
 extern const char *const xml_builtin[][2];
 
+/* Command line option defining whether semihosting should go via gdb or not */
+extern int semihosting_target;
+#define SEMIHOSTING_TARGET_AUTO     0
+#define SEMIHOSTING_TARGET_NATIVE   1
+#define SEMIHOSTING_TARGET_GDB      2
+
 #endif
diff --git a/qemu-options.hx b/qemu-options.hx
index 64af16d..afab995 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -3218,7 +3218,17 @@ DEF("semihosting", 0, QEMU_OPTION_semihosting,
 STEXI
 @item -semihosting
 @findex -semihosting
-Semihosting mode (ARM, M68K, Xtensa only).
+Enable semihosting mode (ARM, M68K, Xtensa only).
+ETEXI
+DEF("semihosting-config", HAS_ARG, QEMU_OPTION_semihosting_config,
+    "-semihosting-config [enable=on|off,]target=native|gdb|auto   semihosting configuration\n",
+QEMU_ARCH_ARM | QEMU_ARCH_M68K | QEMU_ARCH_XTENSA | QEMU_ARCH_LM32)
+STEXI
+@item -semihosting-config [enable=on|off,]target=native|gdb|auto
+@findex -semihosting-config
+Enable semihosting and define where the semihosting calls will be addressed,
+to QEMU (@code{native}) or to GDB (@code{gdb}). The default is @code{auto}, which means
+@code{gdb} during debug sessions and @code{native} otherwise (ARM, M68K, Xtensa only).
 ETEXI
 DEF("old-param", 0, QEMU_OPTION_old_param,
     "-old-param      old param mode\n", QEMU_ARCH_ARM)
diff --git a/vl.c b/vl.c
index eb89d62..7cdfd49 100644
--- a/vl.c
+++ b/vl.c
@@ -554,6 +554,22 @@ static QemuOptsList qemu_icount_opts = {
     },
 };
 
+static QemuOptsList qemu_semihosting_config_opts = {
+    .name = "semihosting-config",
+    .implied_opt_name = "enable",
+    .head = QTAILQ_HEAD_INITIALIZER(qemu_semihosting_config_opts.head),
+    .desc = {
+        {
+            .name = "enable",
+            .type = QEMU_OPT_BOOL,
+        }, {
+            .name = "target",
+            .type = QEMU_OPT_STRING,
+        },
+        { /* end of list */ }
+    },
+};
+
 /**
  * Get machine options
  *
@@ -2811,6 +2827,7 @@ int main(int argc, char **argv, char **envp)
     qemu_add_opts(&qemu_name_opts);
     qemu_add_opts(&qemu_numa_opts);
     qemu_add_opts(&qemu_icount_opts);
+    qemu_add_opts(&qemu_semihosting_config_opts);
 
     runstate_init();
 
@@ -3618,6 +3635,37 @@ int main(int argc, char **argv, char **envp)
 		break;
             case QEMU_OPTION_semihosting:
                 semihosting_enabled = 1;
+                semihosting_target = SEMIHOSTING_TARGET_AUTO;
+                break;
+            case QEMU_OPTION_semihosting_config:
+                semihosting_enabled = 1;
+                opts = qemu_opts_parse(qemu_find_opts("semihosting-config"),
+                                           optarg, 0);
+                if (opts != NULL) {
+                    semihosting_enabled = qemu_opt_get_bool(opts, "enable",
+                                                            true);
+                    const char *target = qemu_opt_get(opts, "target");
+                    if (target != NULL) {
+                        if (strcmp("native", target) == 0) {
+                            semihosting_target = SEMIHOSTING_TARGET_NATIVE;
+                        } else if (strcmp("gdb", target) == 0) {
+                            semihosting_target = SEMIHOSTING_TARGET_GDB;
+                        } else  if (strcmp("auto", target) == 0) {
+                            semihosting_target = SEMIHOSTING_TARGET_AUTO;
+                        } else {
+                            fprintf(stderr, "Unsupported semihosting-config"
+                                    " %s\n",
+                                optarg);
+                            exit(1);
+                        }
+                    } else {
+                        semihosting_target = SEMIHOSTING_TARGET_AUTO;
+                    }
+                } else {
+                    fprintf(stderr, "Unsupported semihosting-config %s\n",
+                            optarg);
+                    exit(1);
+                }
                 break;
             case QEMU_OPTION_tdf:
                 fprintf(stderr, "Warning: user space PIT time drift fix "