[llvm-dev] Updating config.guess, license change

[Michael Kruse via llvm-dev]

Is there a possibility to ask CMake for the host's triple?

Michael

Am Mi., 31. März 2021 um 02:10 Uhr schrieb Harald van Dijk via
llvm-dev <llvm-dev at lists.llvm.org>:
>
> We have a file llvm/cmake/config.guess we inherited from back when we
> had an Autoconf build system, which guesses the triple of the current
> system. As support for new targets get added, this file needs updating
> to detect those new targets. In order to detect a particular target, I
> proposed updating this to the current upstream version, D99625.
>
> When we had an Autoconf build system, this file contained a special
> license exception:
>
> # As a special exception to the GNU General Public License, if you
> # distribute this file as part of a program that contains a
> # configuration script generated by Autoconf, you may include it under
> # the same distribution terms that you use for the rest of that program.
>
> In D16471, the Autoconf build system was removed, so this license
> exception no longer applied and the file became plain GPLv2. As we only
> ever call this script to read its output, rather than including the
> script in some way in the generated LLVM, this should not be a problem:
> the GPLv2 places no restrictions on how its output is used.
>
> The current version is no longer licensed under GPLv2, it is licensed
> under GPLv3, though the license exception remains.
>
> My understanding is that we are on an older version mostly out of
> laziness, not because the GPLv3-licensed version is something we need to
> avoid: we are on the version we happened to use with autoconf, not the
> most recent GPLv2 version. Nonetheless, on review it was suggested to
> bring this change to the list; laziness does not rule out the license
> also potentially being a problem.
>
> So, what is the best way to go here? I think we have three options:
>
> 1- Use the upstream version under GPLv3.
> 2- Use the upstream version along with a dummy configure script
>     generated by Autoconf that just spits out an error saying Autoconf
>     cannot be used to build LLVM.
> 3- Independently add support for new targets to the GPLv2 version of
>     config.guess.
>
> Option 1 has my preference. As we still only call the script and read
> its output, the GPLv3 should be no more a problem than the GPLv2.
> Nonetheless, it would be good to have confirmation that this is okay.
>
> Option 2 very much abuses the spirit of the config.guess license
> exception, so I would like to avoid that.
>
> Option 3 is possible but requires duplicating work already done by upstream.
>
> Thoughts? Comments?
>
> Cheers,
> Harald van Dijk
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