gdbstub: Save target's siginfo

Save target's siginfo into gdbserver_state so it can be used later, for
example, in any stub that requires the target's si_signo and si_code.

This change affects only linux-user mode.

Signed-off-by: Gustavo Romero <gustavo.romero@linaro.org>
Suggested-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20240309030901.1726211-4-gustavo.romero@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

bsd-user/main.c

@@ -606,7 +606,7 @@ int main(int argc, char **argv)
 
     if (gdbstub) {
         gdbserver_start(gdbstub);
-        gdb_handlesig(cpu, 0);
+        gdb_handlesig(cpu, 0, NULL, NULL, 0);
     }
     cpu_loop(env);
     /* never exits */

bsd-user/signal.c

@@ -27,6 +27,9 @@
 #include "hw/core/tcg-cpu-ops.h"
 #include "host-signal.h"
 
+/* target_siginfo_t must fit in gdbstub's siginfo save area. */
+QEMU_BUILD_BUG_ON(sizeof(target_siginfo_t) > MAX_SIGINFO_LENGTH);
+
 static struct target_sigaction sigact_table[TARGET_NSIG];
 static void host_signal_handler(int host_sig, siginfo_t *info, void *puc);
 static void target_to_host_sigset_internal(sigset_t *d,
@@ -889,7 +892,7 @@ static void handle_pending_signal(CPUArchState *env, int sig,
 
     k->pending = 0;
 
-    sig = gdb_handlesig(cpu, sig);
+    sig = gdb_handlesig(cpu, sig, NULL, &k->info, sizeof(k->info));
     if (!sig) {
         sa = NULL;
         handler = TARGET_SIG_IGN;

gdbstub/user.c

@@ -95,6 +95,8 @@ typedef struct {
     enum GDBForkState fork_state;
     int fork_sockets[2];
     pid_t fork_peer_pid, fork_peer_tid;
+    uint8_t siginfo[MAX_SIGINFO_LENGTH];
+    unsigned long siginfo_len;
 } GDBUserState;
 
 static GDBUserState gdbserver_user_state;
@@ -190,7 +192,8 @@ void gdb_qemu_exit(int code)
     exit(code);
 }
 
-int gdb_handlesig(CPUState *cpu, int sig, const char *reason)
+int gdb_handlesig(CPUState *cpu, int sig, const char *reason, void *siginfo,
+                  int siginfo_len)
 {
     char buf[256];
     int n;
@@ -199,6 +202,18 @@ int gdb_handlesig(CPUState *cpu, int sig, const char *reason)
         return sig;
     }
 
+    if (siginfo) {
+        /*
+         * Save target-specific siginfo.
+         *
+         * siginfo size, i.e. siginfo_len, is asserted at compile-time to fit in
+         * gdbserver_user_state.siginfo, usually in the source file calling
+         * gdb_handlesig. See, for instance, {linux,bsd}-user/signal.c.
+         */
+        memcpy(gdbserver_user_state.siginfo, siginfo, siginfo_len);
+        gdbserver_user_state.siginfo_len = siginfo_len;
+    }
+
     /* disable single step if it was enabled */
     cpu_single_step(cpu, 0);
     tb_flush(cpu);
@@ -746,7 +761,7 @@ void gdb_breakpoint_remove_all(CPUState *cs)
 void gdb_syscall_handling(const char *syscall_packet)
 {
     gdb_put_packet(syscall_packet);
-    gdb_handlesig(gdbserver_state.c_cpu, 0, NULL);
+    gdb_handlesig(gdbserver_state.c_cpu, 0, NULL, NULL, 0);
 }
 
 static bool should_catch_syscall(int num)
@@ -764,7 +779,7 @@ void gdb_syscall_entry(CPUState *cs, int num)
 {
     if (should_catch_syscall(num)) {
         g_autofree char *reason = g_strdup_printf("syscall_entry:%x;", num);
-        gdb_handlesig(cs, gdb_target_sigtrap(), reason);
+        gdb_handlesig(cs, gdb_target_sigtrap(), reason, NULL, 0);
     }
 }
 
@@ -772,7 +787,7 @@ void gdb_syscall_return(CPUState *cs, int num)
 {
     if (should_catch_syscall(num)) {
         g_autofree char *reason = g_strdup_printf("syscall_return:%x;", num);
-        gdb_handlesig(cs, gdb_target_sigtrap(), reason);
+        gdb_handlesig(cs, gdb_target_sigtrap(), reason, NULL, 0);
     }
 }
 

include/gdbstub/user.h

@@ -9,11 +9,15 @@
 #ifndef GDBSTUB_USER_H
 #define GDBSTUB_USER_H
 
+#define MAX_SIGINFO_LENGTH 128
+
 /**
  * gdb_handlesig() - yield control to gdb
  * @cpu: CPU
  * @sig: if non-zero, the signal number which caused us to stop
  * @reason: stop reason for stop reply packet or NULL
+ * @siginfo: target-specific siginfo struct
+ * @siginfo_len: target-specific siginfo struct length
  *
  * This function yields control to gdb, when a user-mode-only target
  * needs to stop execution. If @sig is non-zero, then we will send a
@@ -25,7 +29,7 @@
  * or 0 if no signal should be delivered, ie the signal that caused
  * us to stop should be ignored.
  */
-int gdb_handlesig(CPUState *, int, const char *);
+int gdb_handlesig(CPUState *, int, const char *, void *, int);
 
 /**
  * gdb_signalled() - inform remote gdb of sig exit

linux-user/main.c

@@ -1018,7 +1018,7 @@ int main(int argc, char **argv, char **envp)
                     gdbstub);
             exit(EXIT_FAILURE);
         }
-        gdb_handlesig(cpu, 0, NULL);
+        gdb_handlesig(cpu, 0, NULL, NULL, 0);
     }
 
 #ifdef CONFIG_SEMIHOSTING

linux-user/signal.c

@@ -34,6 +34,9 @@
 #include "user/safe-syscall.h"
 #include "tcg/tcg.h"
 
+/* target_siginfo_t must fit in gdbstub's siginfo save area. */
+QEMU_BUILD_BUG_ON(sizeof(target_siginfo_t) > MAX_SIGINFO_LENGTH);
+
 static struct target_sigaction sigact_table[TARGET_NSIG];
 
 static void host_signal_handler(int host_signum, siginfo_t *info,
@@ -1184,7 +1187,7 @@ static void handle_pending_signal(CPUArchState *cpu_env, int sig,
      */
     tswap_siginfo(&k->info, &k->info);
 
-    sig = gdb_handlesig(cpu, sig, NULL);
+    sig = gdb_handlesig(cpu, sig, NULL, &k->info, sizeof(k->info));
     if (!sig) {
         sa = NULL;
         handler = TARGET_SIG_IGN;