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Re: [PATCH v4 6/7] disas: mips: Add micromips R6 disassembler - infrastr

From: Richard Henderson
Subject: Re: [PATCH v4 6/7] disas: mips: Add micromips R6 disassembler - infrastructure and 16-bit instructions
Date: Sat, 25 Jan 2020 08:06:40 -1000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1

On 1/25/20 12:22 AM, Aleksandar Markovic wrote:
> On Saturday, January 25, 2020, Richard Henderson <address@hidden
> <mailto:address@hidden>> wrote:
>     On 1/24/20 1:38 PM, Aleksandar Markovic wrote:
>     > On Friday, January 24, 2020, Richard Henderson
>     <address@hidden <mailto:address@hidden>
>     > <mailto:address@hidden
>     <mailto:address@hidden>>> wrote:
>     >     The thing I'm concerned about here is any future maintenance of this
>     file.  One
>     >     would surely prefer to edit the original decodetree input than this
>     output.
>     >
>     >
>     > Here is the deal: This dissasembler is meant to reflect the
>      documentation of a
>     > particular ISA, and as the documentation largely stays constant (except
>     adding
>     > some insignificant errata), the disassembler will stay virtually 
> constant, we
>     > wouldn't like even to touch it, and we like it this way.
>     No, this is neither right nor proper.
>     To review the code in this form is significantly harder than in its 
> decodetree
>     form.  That is in fact the whole point of the decodetree form: otherwise 
> we'd
>     still be writing these sorts of parsers by hand.
>     While there's no license on this new file (another problem), if as 
> assumed this
>     is GPL 2+, then you are in violation of the GPL.  From section 3:
>       # The source code for a work means the preferred form of
>       # the work for making modifications to it.
>     You cannot with a straight face claim that the generated c is the 
> preferred
>     form for making modifications.
>     Finally, suppose we improve decodetree.py, so that it produces code with 
> which
>     the compiler produces better code, for some metric of better.  We would 
> want
>     this disassembler to benefit as well.
> I think you got some things upside-down. A tool developent and usage should be
> driven by the needs of users of a tool, and not dictated by the author. Users
> should be free to use the tool in any way they seem suitable, including its
> modification.

That's exactly right, provided that by "tool" you mean QEMU and by "users" you
mean everyone downstream of us.

Let me state for the record that I object to this generated file being merged
in this form, for the reasons I stated above.


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