x/sys/unix: ptrace API assumes GOARCH(target) == GOARCH(host)

[4ad]

syscall.PtraceGetRegs uses syscall.PtraceRegs. syscall.PtraceRegs depends on the host, e.g. if your binary is linux/386 syscall.PtraceRegs has 16 registers. But it's possible to run that linux/386 on an amd64 kernel, and attach to an amd64 process. In that case, syscall.PtraceRegs is not good anymore because the amd64 variant has 26 registers.

I have found this while trying to debug an arm64 Go process using an arm Go debugger.

[4ad]

Well, obviously there is nothing we can do about this particular API, because of Go 1 contract, but presumably we can add Ptrace(Get|Set)Regs(386|Amd64) on both 386 and amd64. Thoughts?

[tv42]

Even with Go1 api freeze, golang.org/x/sys/unix can be fixed.

[rsc]

Is it really unfixable without an API change?

[4ad]

Well we can add more precise APIs, leaving the current one (assuming ARCH(target) == ARHC(host)) as is, but that's just adding stuff rather than fixing existing stuff, so I don't consider that as "fixing" anything.

And as for adding stuff, we can add it in some other repository, it doesn't have to be inside syscall.

[bradfitz]

Repurposed this to be about x/sys/unix.

[gopherbot]

Change https://golang.org/cl/73555 mentions this issue: unix: add ptrace definitions for compatible GOARCH pairs