runtime: support for system callbacks with float arguments on Windows #45300
The Windows APIs use certain callbacks with floating point arguments, for example:
To register those from Go code, the
Since the Go calling convention is being reworked (#40724) entirely, this may be a good moment to (try) to address this.
Would be nice to have the support for callbacks with floating point arguments. In this way would be possible to interact with the system using pure Go, without the need of CGo.
I don't know if there are other issues in interacting with Windows APIs, but ideally a full support for interacting with Windows would be great.
Maybe it is worth mentioning that there is a project lead by Microsoft that aims at making WinAPIs more accessible to other languages, by precisely describing them in a metadata format that can be machine processed to get specific language implementations, called projections. With full support of Windows syscall/callbacks, would be possible to make a projection for Go in order to have access to the complete Windows APIs. This is probably best to be discussed in another issue (or elsewhere), but I thought was important to mention here.
As far as I understand, as the comment in the code says, in order for this to work we need to "spill" the floating point registers in order to retrieve the values. This is done in the file runtime/sys_windows_amd64.s.
I am (very) far from being an expert so I don't understand if this is a relatively easy task or a complicated one.
Also I don't really understand why in the C code in Windows SDK headers, callbacks are flagged as
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Thanks for filing this. I don't think it really needs to go through the proposal process. This is something we should just do. We're a bit swamped for 1.17, so it may not happen in the next release, but I've added it to the 1.17 milestone because we already have our hands in that code.
I think this would be relatively easy to do now that we've had to teach NewCallback a lot more about the Go and Windows ABIs in order to support Go's register-based calling convention.
I'm not an expert on Windows calling conventions, but my understanding is that
Thank you for your support.
I was missing something indeed. That link is just for 32 bit systems, the 64 bit section explains the use of