gdbstub: Add syscall entry/return hooks

The upcoming syscall catchpoint support needs to get control on syscall
entry and return. Provide the necessary hooks for that, which are
no-ops for now.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-Id: <20240202152506.279476-4-iii@linux.ibm.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240207163812.3231697-13-alex.bennee@linaro.org>

gdbstub/user.c

@@ -502,3 +502,11 @@ void gdb_syscall_handling(const char *syscall_packet)
     gdb_put_packet(syscall_packet);
     gdb_handlesig(gdbserver_state.c_cpu, 0);
 }
+
+void gdb_syscall_entry(CPUState *cs, int num)
+{
+}
+
+void gdb_syscall_return(CPUState *cs, int num)
+{
+}

include/gdbstub/user.h

@@ -51,5 +51,18 @@ void gdb_signalled(CPUArchState *as, int sig);
  */
 void gdbserver_fork(CPUState *cs);
 
+/**
+ * gdb_syscall_entry() - inform gdb of syscall entry and yield control to it
+ * @cs: CPU
+ * @num: syscall number
+ */
+void gdb_syscall_entry(CPUState *cs, int num);
+
+/**
+ * gdb_syscall_entry() - inform gdb of syscall return and yield control to it
+ * @cs: CPU
+ * @num: syscall number
+ */
+void gdb_syscall_return(CPUState *cs, int num);
 
 #endif /* GDBSTUB_USER_H */

include/user/syscall-trace.h

@@ -11,6 +11,7 @@
 #define SYSCALL_TRACE_H
 
 #include "exec/user/abitypes.h"
+#include "gdbstub/user.h"
 #include "qemu/plugin.h"
 #include "trace/trace-root.h"
 
@@ -20,7 +21,7 @@
  * could potentially unify the -strace code here as well.
  */
 
-static inline void record_syscall_start(void *cpu, int num,
+static inline void record_syscall_start(CPUState *cpu, int num,
                                         abi_long arg1, abi_long arg2,
                                         abi_long arg3, abi_long arg4,
                                         abi_long arg5, abi_long arg6,
@@ -29,11 +30,13 @@ static inline void record_syscall_start(void *cpu, int num,
     qemu_plugin_vcpu_syscall(cpu, num,
                              arg1, arg2, arg3, arg4,
                              arg5, arg6, arg7, arg8);
+    gdb_syscall_entry(cpu, num);
 }
 
-static inline void record_syscall_return(void *cpu, int num, abi_long ret)
+static inline void record_syscall_return(CPUState *cpu, int num, abi_long ret)
 {
     qemu_plugin_vcpu_syscall_ret(cpu, num, ret);
+    gdb_syscall_return(cpu, num);
 }