amd64: Add static asssert for context size

[imp]

Summary

Add a static assert for the mcontext{,32}_t and ucontext{,32}_t
sizes. These are de-facto ABI options and cannot change size ever.

Sponsored by: Netflix

[kib]

sys/amd64/amd64/exec_machdep.c

100

The compat32 asserts should go somewhere in amd64/ia32/ or even compat/ia32.

Indeed, look at compat/ia32/ia32_sysvec.c:78.

[imp]

sys/amd64/amd64/exec_machdep.c

100

Sure. Looks like I should add siginfo_t as well... I can just remove these and I'll see if there's a more appropriate place for the armv7 ones.

thanks

[imp]

update per review

[kib]

sys/amd64/amd64/exec_machdep.c

100

siginfo is in fact MI, it is LP64 vs ILP32 at most. You should see it yourself when you added asserts. I belive sys/kern_sig.c would be a better place for such assert, with ABI ifdef.

But I do not insist.

[imp]

sys/amd64/amd64/exec_machdep.c

100

I think I'm leaning towards keeping this here because it is MD, even if its size is predictable based on LP64 vs ILP32. There's no code that depends on that happy accident (other than sizes). If there were, I'd be inclined to move it near that code.

[andrew]

sys/amd64/amd64/exec_machdep.c

99

Shouldn't this message be ucontext_t ...?

[imp]

update per review