cmd/cgo: add support for pre-compiled cgo packages #38917
This is the GitHub issue for my half-baked proposal posted on golang-dev.
Packages that import "C" require quite a lot of support software:
On the other hand, it's not always possible to avoid C dependencies: Gio uses
One option is .syso files (https://github.com/golang/go/wiki/GcToolchainTricks),
So I wonder: can you imagine a Goldilocks option where a package can have access
I wouldn't mind if the hypothetical cgo file format changes once in a while, say every Go
As a strawman, I suggest a way to invoke
which then outputs, say, <package_go115>.cgo. If is later built, possibly on a different
With pre-compiled Cgo the building process is faster, and I can avoid having the headers and development libraries available for my target platform, needing only a native toolchain for external linking.
What's really interesting is then adding support for
In other words, pre-generated cgo could give Cgo programs some of the nice cross-platform properties of pure Go programs.
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This is exactly what I wanted to do ad-hoc for SQLite, would love to see it!
I think there wouldn't even be any need for new
This actually means it could be a fully external tool, at least for prototyping. Indeed, the thing that needs toolchain support is #38918, which is where things get interesting.
Indeed. What I'd like to achieve first is some indication that work towards pre-generation may end up in the main repository. I don't fancy maintaining an out-of-tree tool.
I don't really understand how to do this in general.
cgo packages can and do refer to external libraries; presumably we would have to find all of those external libraries and make them available somewhere. But the libraries are going to vary a lot. How do we find them and where do we put them?
Some of those libraries are written in C++. C++ code requires extra work from the linker to support things like global constructors and destructors and exception handling. If we can't invoke the external linker, we have to implement all of that code in cmd/link, and we have to maintain it as C++ changes.
Maybe I'm missing something, but while I can see how this could work in the simplest cases, I don't see how it could work in general.
Can we ask the native toolchain while pre-pregenerating, in a similar way Cgo currently asks the toolchain about the structure of native types, functions etc.?
My use-case is system libraries, which are usually designed to have simple C (or Objective-C) interfaces as well as being impossible to replace with Go by definition. Having pre-generation work on a best-effort basis would be ok for me, I would simply not provide pre-generated files for the platforms/libraries that are not (yet) supported.