Segment register reading on Windows targets.

This patch makes sure that the value of segment registers are
read properly as 16bit values on Windows.

gdb/ChangeLog:

        * windows-nat.h (segment_register_p_ftype): New typedef.
        (windows_set_segment_register_p): Add declaration.
        * windows-nat.c (segment_register_p): New static global.
        (windows_set_segment_register_p): New function.
        (do_windows_fetch_inferior_registers): Add special handling
        for segment registers.
        * amd64-windows-nat.c: #include "amd64-tdep.h".
        (amd64_windows_segment_register_p): New function.
        (_initialize_amd64_windows_nat): Call windows_set_segment_register_p.
        * i386-windows-nat.c: #include "i386-tdep.h".
        (i386_windows_segment_register_p): New function.
        (_initialize_i386_windows_nat): Call windows_set_segment_register_p.

1 files changed, 20 insertions, 0 deletions

diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index f536ed1ce95..000c86f5ccc 100644
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -243,6 +243,10 @@ static int useshell = 0;		/* use shell for subprocesses */
 
 static const int *mappings;
 
+/* The function to use in order to determine whether a register is
+   a segment register or not.  */
+static segment_register_p_ftype *segment_register_p;
+
 /* This vector maps the target's idea of an exception (extracted
    from the DEBUG_EVENT structure) to GDB's idea.  */
 
@@ -272,6 +276,14 @@ windows_set_context_register_offsets (const int *offsets)
   mappings = offsets;
 }
 
+/* See windows-nat.h.  */
+
+void
+windows_set_segment_register_p (segment_register_p_ftype *fun)
+{
+  segment_register_p = fun;
+}
+
 static void
 check (BOOL ok, const char *file, int line)
 {
@@ -456,6 +468,14 @@ do_windows_fetch_inferior_registers (struct regcache *regcache, int r)
       l = (*((long *) context_offset) >> 16) & ((1 << 11) - 1);
       regcache_raw_supply (regcache, r, (char *) &l);
     }
+  else if (segment_register_p (r))
+    {
+      /* GDB treats segment registers as 32bit registers, but they are
+	 in fact only 16 bits long.  Make sure we do not read extra
+	 bits from our source buffer.  */
+      l = *((long *) context_offset) & 0xffff;
+      regcache_raw_supply (regcache, r, (char *) &l);
+    }
   else if (r >= 0)
     regcache_raw_supply (regcache, r, context_offset);
   else