Re: [RFA][2/5] New port: Cell BE SPU (valops.c fix)

["Ulrich Weigand" <uweigand@de.ibm.com>]

Daniel Jacobowitz wrote:

> Does the same thing happen for struct { char w, x, y, z; }?

For some reason I seem unable to convince GCC to place such
a struct into a register.

However, when attempting to manipulate a register directly
using its type structure, I'm seeing the same problem:

(gdb) print $r3
$1 = {uint128 = 0x00000001000000000000000000000000, v4_float = {1.40129846e-45, 0, 0, 0}, v4_int32 = {1, 0, 0, 0},
  v8_int16 = {0, 1, 0, 0, 0, 0, 0, 0}, v16_int8 = "\000\000\000\001", '\0' <repeats 11 times>}
(gdb) print $r3.v4_int32
$2 = {1, 0, 0, 0}
(gdb) print $r3.v4_int32[2]
$3 = 0
(gdb) set variable $r3.v4_int32[2] = 5
(gdb) print $r3.v4_int32
$4 = {5, 0, 0, 0}


For registers without special conversion function, value_assign
performs a read-modify-write cycle: it reads the old contents 
of the register(s), modify the bits denoted by value_offset,
value_bitsize and value_bitpos, and writes the full register
contents back.

Maybe we need to do a similar cycle of REGISTER_TO_VALUE,
modify selected bits, VALUE_TO_REGISTER for the registers with
special conversion function?

As an aside, what is this code in value_assign supposed to do:

            /* Locate the first register that falls in the value that
               needs to be transfered.  Compute the offset of the
               value in that register.  */
            {
              int offset;
              for (reg_offset = value_reg, offset = 0;
                   offset + register_size (current_gdbarch, reg_offset) <= value_offset (toval);
                   reg_offset++);
              byte_offset = value_offset (toval) - offset;
            }

It seems clearly broken (offset remains constant 0), but I'm not
quite sure what the intent was.

Bye,
Ulrich

-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com