[PATCH 2/7] semihosting: add the semihosting_exit_request function

[Luc Michel]

Add the semihosting_exit_request function to be used by targets when
handling an `exit' semihosted syscall. This function calls gdb_exit to
close existing GDB connections, and qemu_system_shutdown_request with
the new `guest-semi-exit' exit reason. It sets the QEMU exit status
given by the exit syscall parameter. Finally it stops the CPU to prevent
further execution, and exit the CPU loop as the syscall caller expects
this syscall to not return.

This function is meant to be used in place of a raw exit() call when
handling semihosted `exit' syscalls. Such a call is not safe because
it does not allow other CPU threads to exit properly, leading to e.g.
at_exit callbacks being called while other CPUs still run. This can lead
to strange bugs, especially in plugins with a registered at_exit function.

Signed-off-by: Luc Michel <lmichel@kalray.eu>
---
 qapi/run-state.json            |  4 +++-
 include/semihosting/semihost.h |  4 ++++
 semihosting/config.c           | 17 +++++++++++++++++
 3 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/qapi/run-state.json b/qapi/run-state.json
index 6e2162d7b3..a4f08dd32e 100644
--- a/qapi/run-state.json
+++ b/qapi/run-state.json
@@ -80,20 +80,22 @@
 # @guest-reset: Guest reset request, and command line turns that into
 #               a shutdown
 #
 # @guest-panic: Guest panicked, and command line turns that into a shutdown
 #
+# @guest-semi-exit: Guest exit request via a semi-hosted exit syscall
+#
 # @subsystem-reset: Partial guest reset that does not trigger QMP events and
 #                   ignores --no-reboot. This is useful for sanitizing
 #                   hypercalls on s390 that are used during kexec/kdump/boot
 #
 ##
 { 'enum': 'ShutdownCause',
   # Beware, shutdown_caused_by_guest() depends on enumeration order
   'data': [ 'none', 'host-error', 'host-qmp-quit', 'host-qmp-system-reset',
             'host-signal', 'host-ui', 'guest-shutdown', 'guest-reset',
-            'guest-panic', 'subsystem-reset'] }
+            'guest-panic', 'guest-semi-exit', 'subsystem-reset'] }
 
 ##
 # @StatusInfo:
 #
 # Information about VCPU run state
diff --git a/include/semihosting/semihost.h b/include/semihosting/semihost.h
index 0c55ade3ac..9a3214a0c8 100644
--- a/include/semihosting/semihost.h
+++ b/include/semihosting/semihost.h
@@ -54,10 +54,13 @@ static inline const char *semihosting_get_cmdline(void)
 
 static inline Chardev *semihosting_get_chardev(void)
 {
     return NULL;
 }
+void semihosting_exit_request(int status)
+{
+}
 static inline void qemu_semihosting_console_init(void)
 {
 }
 #else /* !CONFIG_USER_ONLY */
 bool semihosting_enabled(void);
@@ -65,10 +68,11 @@ SemihostingTarget semihosting_get_target(void);
 const char *semihosting_get_arg(int i);
 int semihosting_get_argc(void);
 const char *semihosting_get_cmdline(void);
 void semihosting_arg_fallback(const char *file, const char *cmd);
 Chardev *semihosting_get_chardev(void);
+G_NORETURN void semihosting_exit_request(int status);
 /* for vl.c hooks */
 void qemu_semihosting_enable(void);
 int qemu_semihosting_config_options(const char *opt);
 void qemu_semihosting_connect_chardevs(void);
 void qemu_semihosting_console_init(void);
diff --git a/semihosting/config.c b/semihosting/config.c
index 3afacf54ab..7913c83033 100644
--- a/semihosting/config.c
+++ b/semihosting/config.c
@@ -22,10 +22,15 @@
 #include "qemu/option.h"
 #include "qemu/config-file.h"
 #include "qemu/error-report.h"
 #include "semihosting/semihost.h"
 #include "chardev/char.h"
+#include "sysemu/sysemu.h"
+#include "sysemu/runstate.h"
+#include "sysemu/cpus.h"
+#include "exec/exec-all.h"
+#include "exec/gdbstub.h"
 
 QemuOptsList qemu_semihosting_config_opts = {
     .name = "semihosting-config",
     .merge_lists = true,
     .implied_opt_name = "enable",
@@ -183,5 +188,17 @@ void qemu_semihosting_connect_chardevs(void)
             exit(1);
         }
         semihosting.chardev = chr;
     }
 }
+
+void semihosting_exit_request(int status)
+{
+    gdb_exit(status);
+    qemu_set_exit_status(status);
+    qemu_system_shutdown_request(SHUTDOWN_CAUSE_GUEST_SEMI_EXIT);
+    cpu_stop_current();
+
+    current_cpu->exception_index = EXCP_HLT;
+    current_cpu->halted = 1;
+    cpu_loop_exit(current_cpu);
+}
-- 
2.17.1