Can I force a word read-modify-write instread of a byte write?

["Phil Endecott" <spam_from_gcc_help at chezphil dot org>]

Dear Experts,

I know that in some circumstances gcc will generate read-modify-write 
sequences to access memory locations, for example if I have a bitfield 
struct.  Is there a way in which I can tell it to only do (32-bit) word 
writes to a region of memory, and to do read-modify-write sequences 
instead of byte writes, even though the processor does have byte write instructions?

The situation is that I have some FPGA logic which only implements word 
writes.  My options are:

(a) Make the FPGA hardware support byte writes.
(b) Do explicit read/modify/write sequences in my C code.
(c) Persuade gcc to do the work for me.

Since both (a) and (b) involve quite a lot of work, I have crossed my 
fingers in the hope that I can just add some magic __attribute__ 
somewhere and gcc will do the work for me.  Am I in luck?


Many thanks for any suggestions,

Phil.