PATCH: Check DS segment register for x32 process

["H.J. Lu" <hongjiu dot lu at intel dot com>]

Hi,

This patch checks DS segment register for x32 process.  Tested on
Linux/x86-64.  OK to install?

Thanks.

H.J.
---
	* amd64-linux-nat.c (AMD64_LINUX_X32_DS): New.
	(amd64_linux_read_description): Check DS segment register for
	x32 process.

diff --git a/gdb/amd64-linux-nat.c b/gdb/amd64-linux-nat.c
index 3be8404..97c9a49 100644
--- a/gdb/amd64-linux-nat.c
+++ b/gdb/amd64-linux-nat.c
@@ -756,16 +945,23 @@ amd64_linux_siginfo_fixup (siginfo_t *native, gdb_byte *inf, int direction)
    Value of CS segment register:
      1. 64bit process: 0x33.
      2. 32bit process: 0x23.
+
+   Value of DS segment register:
+     1. LP64 process: 0x0.
+     2. X32 process: 0x2b.
  */
 
 #define AMD64_LINUX_USER64_CS	0x33
+#define AMD64_LINUX_X32_DS	0x2b
 
 static const struct target_desc *
 amd64_linux_read_description (struct target_ops *ops)
 {
   unsigned long cs;
+  unsigned long ds;
   int tid;
   int is_64bit;
+  int is_x32;
   static uint64_t xcr0;
 
   /* GNU/Linux LWP ID's are process ID's.  */
@@ -782,6 +978,18 @@ amd64_linux_read_description (struct target_ops *ops)
 
   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"));
+
+  is_x32 = ds == AMD64_LINUX_X32_DS;
+
+  if (sizeof (void *) == 4 && is_64bit && !is_x32)
+    error (_("Can't debug 64-bit process with 32-bit GDB"));
+
   if (have_ptrace_getregset == -1)
     {
       uint64_t xstateregs[(I386_XSTATE_SSE_SIZE / sizeof (uint64_t))];
@@ -809,14 +1017,24 @@ amd64_linux_read_description (struct target_ops *ops)
       && (xcr0 & I386_XSTATE_AVX_MASK) == I386_XSTATE_AVX_MASK)
     {
       if (is_64bit)
-	return tdesc_amd64_avx_linux;
+	{
+	  if (is_x32)
+	    return tdesc_x32_avx_linux;
+	  else
+	    return tdesc_amd64_avx_linux;
+	}
       else
 	return tdesc_i386_avx_linux;
     }
   else
     {
       if (is_64bit)
-	return tdesc_amd64_linux;
+	{
+	  if (is_x32)
+	    return tdesc_x32_linux;
+	  else
+	    return tdesc_amd64_linux;
+	}
       else
 	return tdesc_i386_linux;
     }