2 files changed, 75 insertions, 0 deletions
diff --git a/gdb/nat/x86-linux.c b/gdb/nat/x86-linux.c
index e61f4d7..4242a1b 100644
--- a/gdb/nat/x86-linux.c
+++ b/gdb/nat/x86-linux.c
@@ -20,6 +20,8 @@
 #include "gdbsupport/common-defs.h"
 #include "x86-linux.h"
 #include "x86-linux-dregs.h"
+#include "nat/gdb_ptrace.h"
+#include <sys/user.h>
 
 /* Per-thread arch-specific data we want to keep.  */
 
@@ -80,3 +82,48 @@ x86_linux_prepare_to_resume (struct lwp_info *lwp)
 {
   x86_linux_update_debug_registers (lwp);
 }
+
+#ifdef __x86_64__
+/* Value of CS segment register:
+     64bit process: 0x33
+     32bit process: 0x23  */
+#define AMD64_LINUX_USER64_CS 0x33
+
+/* Value of DS segment register:
+     LP64 process: 0x0
+     X32 process: 0x2b  */
+#define AMD64_LINUX_X32_DS 0x2b
+#endif
+
+/* See nat/x86-linux.h.  */
+
+x86_linux_arch_size
+x86_linux_ptrace_get_arch_size (int tid)
+{
+#ifdef __x86_64__
+  unsigned long cs;
+  unsigned long ds;
+
+  /* Get CS register.  */
+  errno = 0;
+  cs = ptrace (PTRACE_PEEKUSER, tid,
+	       offsetof (struct user_regs_struct, cs), 0);
+  if (errno != 0)
+    perror_with_name (_("Couldn't get CS register"));
+
+  bool is_64bit = cs == AMD64_LINUX_USER64_CS;
+
+  /* Get DS register.  */
+  errno = 0;
+  ds = ptrace (PTRACE_PEEKUSER, tid,
+	       offsetof (struct user_regs_struct, ds), 0);
+  if (errno != 0)
+    perror_with_name (_("Couldn't get DS register"));
+
+  bool is_x32 = ds == AMD64_LINUX_X32_DS;
+
+  return x86_linux_arch_size (is_64bit, is_x32);
+#else
+  return x86_linux_arch_size (false, false);
+#endif
+}
diff --git a/gdb/nat/x86-linux.h b/gdb/nat/x86-linux.h
index 8228821..15153ea 100644
--- a/gdb/nat/x86-linux.h
+++ b/gdb/nat/x86-linux.h
@@ -47,4 +47,32 @@ extern void x86_linux_delete_thread (struct arch_lwp_info *arch_lwp);
 
 extern void x86_linux_prepare_to_resume (struct lwp_info *lwp);
 
+/* Return value from x86_linux_ptrace_get_arch_size function.  Indicates if
+   a thread is 32-bit, 64-bit, or x32.  */
+
+struct x86_linux_arch_size
+{
+  explicit x86_linux_arch_size (bool is_64bit, bool is_x32)
+    : m_is_64bit (is_64bit),
+      m_is_x32 (is_x32)
+  {
+    /* Nothing.  */
+  }
+
+  bool is_64bit () const
+  { return m_is_64bit; }
+
+  bool is_x32 () const
+  { return m_is_x32; }
+
+private:
+  bool m_is_64bit = false;
+  bool m_is_x32 = false;
+};
+
+/* Use ptrace calls to figure out if thread TID is 32-bit, 64-bit, or
+   64-bit running in x32 mode.  */
+
+extern x86_linux_arch_size x86_linux_ptrace_get_arch_size (int tid);
+
 #endif /* NAT_X86_LINUX_H */