[Qemu-devel] [PATCH v2] Add the "-semihosting-config" option.

[Liviu Ionescu <ilg@livius.net>]

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>
---
 gdbstub.c               | 13 +++++++++++--
 include/sysemu/sysemu.h |  6 ++++++
 qemu-options.hx         | 12 +++++++++++-
 vl.c                    | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 77 insertions(+), 3 deletions(-)

diff --git a/gdbstub.c b/gdbstub.c
index 0faca56..982f039 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -351,10 +351,19 @@ 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/sysemu/sysemu.h b/include/sysemu/sysemu.h
index 9fea3bc..c145d94 100644
--- a/include/sysemu/sysemu.h
+++ b/include/sysemu/sysemu.h
@@ -127,7 +127,13 @@ extern int cursor_hide;
 extern int graphic_rotate;
 extern int no_quit;
 extern int no_shutdown;
+
 extern int semihosting_enabled;
+extern int semihosting_target;
+#define SEMIHOSTING_TARGET_AUTO     0
+#define SEMIHOSTING_TARGET_NATIVE   1
+#define SEMIHOSTING_TARGET_GDB      2
+
 extern int old_param;
 extern int boot_menu;
 extern bool boot_strict;
diff --git a/qemu-options.hx b/qemu-options.hx
index da9851d..3e81222 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -3216,7 +3216,17 @@ 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 f4a6e5e..8844983 100644
--- a/vl.c
+++ b/vl.c
@@ -172,6 +172,7 @@ const char *watchdog;
 QEMUOptionRom option_rom[MAX_OPTION_ROMS];
 int nb_option_roms;
 int semihosting_enabled = 0;
+int semihosting_target = SEMIHOSTING_TARGET_AUTO;
 int old_param = 0;
 const char *qemu_name;
 int alt_grab = 0;
@@ -554,6 +555,22 @@ 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 +2828,7 @@ 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 +3636,37 @@ 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 "
-- 
1.9.3 (Apple Git-50)