Add a common utility function to read and write siginfo_t in inferior

gdb/ChangeLog:

        * netbsd-nat.h (netbsd_nat::qxfer_siginfo): Add.
        * netbsd-nat.c (netbsd_nat::qxfer_siginfo): Likewise.

gdb/ChangeLog

@@ -1,3 +1,8 @@
+2020-09-10  Kamil Rytarowski  <n54@gmx.com>
+
+	* netbsd-nat.h (netbsd_nat::qxfer_siginfo): Add.
+	* netbsd-nat.c (netbsd_nat::qxfer_siginfo): Likewise.
+
 2020-09-10  Kamil Rytarowski  <n54@gmx.com>
 
 	* netbsd-nat.h (netbsd_nat::enable_proc_events): Add.

gdb/nat/netbsd-nat.c

@@ -181,4 +181,33 @@ enable_proc_events (pid_t pid)
     perror_with_name (("ptrace"));
 }
 
+/* See netbsd-nat.h.  */
+
+int
+qxfer_siginfo (pid_t pid, const char *annex, unsigned char *readbuf,
+	       unsigned const char *writebuf, CORE_ADDR offset, int len)
+{
+  ptrace_siginfo_t psi;
+
+  if (offset > sizeof (siginfo_t))
+    return -1;
+
+  if (ptrace (PT_GET_SIGINFO, pid, &psi, sizeof (psi)) == -1)
+    return -1;
+
+  if (offset + len > sizeof (siginfo_t))
+    len = sizeof (siginfo_t) - offset;
+
+  if (readbuf != NULL)
+    memcpy (readbuf, ((gdb_byte *) &psi.psi_siginfo) + offset, len);
+  else
+    {
+      memcpy (((gdb_byte *) &psi.psi_siginfo) + offset, writebuf, len);
+
+      if (ptrace (PT_SET_SIGINFO, pid, &psi, sizeof (psi)) == -1)
+	return -1;
+    }
+  return len;
+}
+
 }

gdb/nat/netbsd-nat.h

@@ -57,6 +57,16 @@ extern void for_each_thread (pid_t pid,
    traced.  */
 
 extern void enable_proc_events (pid_t pid);
+
+/* Implement reading and writing of inferior's siginfo_t specified by PID.
+   Returns -1 on failure and the number of bytes on a successful transfer.
+
+   This function assumes internally that the queried process is stopped and
+   traced.  */
+
+extern int qxfer_siginfo (pid_t pid, const char *annex, unsigned char *readbuf,
+			  unsigned const char *writebuf, CORE_ADDR offset,
+			  int len);
 }
 
 #endif