read_frame_register_value and big endian arches

The read_frame_register_value function as it was implemented introduced
a regression on big-endian targets. The problem appears when trying to
get the value of an entity stored inside a register, and when the size
of the entity is smaller than the size of the register. In that case,
we were always reading the first N bytes of the register, which is wrong
for big-endian architectures, where we need to read the last N bytes of
the register.

gdb/ChangeLog:

        * findvar.c (read_frame_register_value): Read correct bytes from
        register on big-endian architectures.

gdb/testsuite/ChangeLog:

        * gdb.ada/small_reg_param: New testcase.

1 files changed, 11 insertions, 3 deletions

diff --git a/gdb/findvar.c b/gdb/findvar.c
index 54e7b4a..426b488 100644
--- a/gdb/findvar.c
+++ b/gdb/findvar.c
@@ -641,11 +641,19 @@ read_frame_register_value (struct value *value, struct frame_info *frame)
     {
       struct value *regval = get_frame_register_value (frame, regnum);
       int reg_len = TYPE_LENGTH (value_type (regval));
+      int reg_offset = 0;
 
+      /* If the register length is larger than the number of bytes
+         remaining to copy, then only copy the appropriate bytes.  */
       if (offset + reg_len > len)
-        reg_len = len - offset;
-      value_contents_copy (value, offset, regval, value_offset (regval),
-			   reg_len);
+	{
+	  reg_len = len - offset;
+	  if (gdbarch_byte_order (get_frame_arch (frame)) == BFD_ENDIAN_BIG)
+	    reg_offset = TYPE_LENGTH (value_type (regval)) - reg_len;
+	}
+
+      value_contents_copy (value, offset, regval,
+                           value_offset (regval) + reg_offset, reg_len);
 
       offset += reg_len;
       regnum++;