Hi Robert,

Are you trying to reduce compilation time of gem5 itself by bypassing the
decoder description, or are you trying to add the ability to specify custom
instructions in a simulation script so gem5 doesn't have to be recompiled
at all to add new ones?

-Alec Roelke

On Thu, Feb 8, 2018 at 10:34 AM, Robert Scheffel <
robert.scheff...@tu-dresden.de> wrote:

> Hi all,
>
> as part of my diploma thesis I want to implement an interface for custom
> instructions for the RISC-V ISA.
> The goal is to have a mechanism (plug-in, ...) where a user can easily add
> an instruction, define its opcode and its behaviour without touching the
> decoder.
>
> As changing the underlying decoder results in recompiling and rebuilding
> of almost the whole binary, I think it might be better to define entry
> points in the decoder that give control to a decoding function within a
> plug-in.
> This way the decoder doesn't need to be touched, when a new instruction is
> added.
> A first idea, that comes to my mind, is to describe the behaviour and
> opcodes in a C++ file. From all existing descriptions a custom decoder is
> generated, that takes over decoding, once the gem5 decoder reaches the
> entry point for custom instructions.
>
> Do you see any problem with this approach? Is there a better way to
> implement such an interface?
>
> Kind regards
>
> Robert
>
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