This patch adds information about _sigsys structure from newer kernels, so that
$_siginfo decoding can show information about _sigsys, making it easier for
developers to debug seccomp failures.

Code is copied from suggested patch for this issue in
https://sourceware.org/bugzilla/show_bug.cgi?id=24283.

This fixes crosbug/937009.

Author: cmtice@google.com
Date: 09-Mar-2021
diff --git a/gdb/linux-tdep.c b/gdb/linux-tdep.c
index 59d04c4..c52d425 100644
--- a/gdb/linux-tdep.c
+++ b/gdb/linux-tdep.c
@@ -350,6 +350,13 @@ linux_get_siginfo_type_with_fields (struct gdbarch *gdbarch,
   append_composite_type_field (type, "si_fd", int_type);
   append_composite_type_field (sifields_type, "_sigpoll", type);
 
+  /* _sigsys */
+  type = arch_composite_type (gdbarch, NULL, TYPE_CODE_STRUCT);
+  append_composite_type_field (type, "_call_addr", void_ptr_type);
+  append_composite_type_field (type, "_syscall", int_type);
+  append_composite_type_field (type, "_arch", uint_type);
+  append_composite_type_field (sifields_type, "_sigsys", type);
+
   /* struct siginfo */
   siginfo_type = arch_composite_type (gdbarch, NULL, TYPE_CODE_STRUCT);
   TYPE_NAME (siginfo_type) = xstrdup ("siginfo");