is it possible to statically override malloc for cgo?

[jhance]

I can't find anything online about doing this (bazel or not), but it would be nice if go_binary could expose malloc attribute (like cc_binary, maybe named cgo_malloc in this case) and/or support --custom_malloc. I could not find an existing way to make this work.

Use case: some go programs might be primarily cgo calls around larger C++ libraries (like for ml) and it would be nice to be able to use mimalloc or tcmalloc there. Presumably this can work with LD_PRELOAD but I was hoping for a static solution.

[fmeum]

Supporting --custom_malloc would be great as a starting point that adds no new API. Since it's possible to transition this flag per target, this would also provide a way to configure this per target.

Would you be interested in working on this? If you need any kind of support let me know.

[jhance]

I am! But I have zero idea how cgo works so I'm not sure where to start. I understand from the cc_binary implementation that I can access the custom_malloc option off the cpp fragment (is there a better way?). But I'm not sure where to glue it in.

Does cgo link once per library that has cgo dependencies or is everything handled at the top level link?

[fmeum]

Getting it from the cpp fragment is the best way to handle it at this point.

@jayconrod Would you expect Go to work with a custom malloc for cgo - I guess the runtime doesn't use anything from libc?

[jayconrod]

I don't know of any reason Go wouldn't work with a custom malloc. The runtime is purely in Go and assembly and can be built without a C toolchain, but there are a few optional C bits. Still, I doubt they're sensitive to what malloc does under the hood.

I imagine this can be done as part of the C++ toolchain configuration, and I think that would be preferably to changing the Go configuration. But I'm not sure how to do it... the C++ toolchain configuration has changed a lot since I looked.

[jhance]

I suppose it would be nice if this was handled in like cc_common.link rather than in cc_binary? But I am not sure if it is easy to edit rules_cc yet, did it finish starlarkification?