Re: Encoding of immediates different to label addresses

On 02/01/2012 09:44, Julius Baxter wrote:
> I'm working on fixing up the OpenRISC 1000 CGEN port and have come
> across something I find I can't quite do with CGEN.
>
> For the jump and branch instructions, if we use immediate value number
> specified in the assembly, we need that encoded into the instruction
> without any shifting occurring to it.
>
> Eg. "l.bf 1" should become 0x10000001, "l.bf 4" should become 0x10000004 etc.
>
> These target addresses are shifted-left by two during decoding, and so
> "l.bf 1" is actually a branch of 4 bytes.
>
> If we use a label for an address, though, I'm seeing that we're
> getting the offset in bytes during encoding, which then needs to be
> shifted right by two before being put in the instruction.
>
> But it seems we can have the shifting on both numerical immediates and
> labels, or neither. (Pardon my incorrect use of terminology, I have a
> feeling I'm not quite calling everything its right name!)
>
> Upon inspecttion, it looks like the binutils port we have been using
> for the past few years (not CGEN-based) has a right-shift of 2 in the
> md_apply_fix() function in binutils/gas/config/tc-or32.c (
> http://sourceware.org/git/?p=binutils.git;a=blob;f=gas/config/tc-or32.c;h=7234fb837e006f979c255f62206e39a9822046d2;hb=HEAD#l603
> ) when the instruction had the actual value of the label inserted into
> it.
>
> Is there any way to handle this using the CGEN description?