The plugin is potentially a derivative work of both Yosys and GHDL, but that's fine - it's possible to comply with the requirements of both the MIT license and the GPLv2 at the same time. The resulting work is GPLv2-licensed. (To be precise, you also need to preserve any copyright notices from the MIT-licensed project and the text of the MIT license. The MIT license has only one condition, but you do need to follow it, same as if you were building proprietary software with an MIT-licensed component.) If anyone distributes Yosys with the plugin, the combined work must also be distributed under GPLv2, which is also fine.

In this case, perf is (like the Linux kernel, in whose git tree it lives) GPLv2-only, and modern versions of libbfd are GPLv3-or-later, and it's not possible to comply with both at the same time. The GPLv2 has a "no additional restrictions" clause, and the GPLv3 asks for things the GPLv2 does not. So a distributor of a combined system including perf built against libbfd (like a Linux distro) cannot comply with the licenses.

(I suppose perf was written against the libbfd API back when libbfd was GPLv2, avoiding the question of whether perf is an illegal derivative work of libbfd. Or the backtracing API is de minimis, which means the source is fine but a compiled binary as par of a distro that also includes a modern libbfd is not.)

One possible answer here is to ask the perf authors to relicense under GPLv2 or later. Many years ago, at a startup that no longer exists, I wanted to reuse code from the Linux kernel "dm-verity" module in GRUB, which had moved to GPLv3, and I got a pretty quick answer from Red Hat (who was the only copyright holder for those files) saying that would be fine.

Your answer and the one from another commenter mention distribution.

In this spirit, is there any legal issue with downloading perf and libbfd separately, compiling it, and running using it for yourself only? I assume not?

What about using it then as a tool within your company? That might be seen as distribution, and thus not allowed?

There's no legal issue with using it yourself. Debian's problem is that, as a distro, they are creating a single product - the Debian operating system.

Debian could even ship you something that compiles perf against libbfd on your own system. This is the approach they take with ZFS and Linux, which are under incompatible licenses (CDDL and GPLv2): https://bits.debian.org/2016/05/what-does-it-mean-that-zfs-i...

A company is generally a single legal person and so there's no "distribution", but https://www.jolts.world/index.php/jolts/article/view/66/125 is a law review article that discusses the complexities here. If you employ contractors, or if the company as a whole is purchased, the answer is apparently blurrier.

Thanks!

My understanding is that there’s only a problem if the distributor combines the two things: if the main application is one license and the plug-in a different one, it’s not a license violation for the end-user to combine the two (unless they turn around and become a distributor in some way).

I am pretty sure that depends on the intent of your distribution. If your software is useless with the plugin and you go "wink wink nudge nudge use this plugin to make this work" this would probably be infringement. If your software is functional without this, and you just happen to have the ability to load plugins of which this is one of them, then it's much better.