Support breakpoint intrinsic

[syvb]

The breakpoint intrinsic raises a SIGTRAP signal. If a debugger is attached to a normal program, then SIGTRAP can be used to trigger breakpoints in debuggers like gdb. If there is no debugger, then the program exits with a message like Trace/breakpoint trap (core dumped). This adds support for the intrinsic in Miri. While actually passing through the SIGTRAP doesn't make sense in a Miri context (if it just raised the signal normally then it would allow for debugging Miri itself, not the program being evaluated). As such, it just raises an error.

[bjorn3]

Can you expose some way for priroda to intercept the breakpoint and later continue execution?

[RalfJung]

@bjorn3 can't Priroda just intercept intrinsic calls and handle brekapoint before falling back to Miri's intrinsic handling?

[bjorn3]

@bjorn3 can't Priroda just intercept intrinsic calls and handle brekapoint before falling back to Miri's intrinsic handling?

The Frame's current_loc is read-only. This means that I think the only way to intercept the intrinsic call would be to duplicate miri's EvalContext.

[RalfJung]

The Frame's current_loc is read-only. This means that I think the only way to intercept the intrinsic call would be to duplicate miri's EvalContext.

I don't see what the first sentence has to do with the second. And I expected Priroda anyway has its own EvalContext implementation that just calls the Miri methods as fallbacks? No code would have to be duplicated, just the signatures, right?

[RalfJung]

What other method do you suggest for Priroda to hook breakpoints? Does that have to block the PR? It's not like the PR makes things any worse here for Priroda, right? It seems unfair to expect @Smittyvb, a first time-contributor, to develop such a system.

[bjorn3]

And I expected Priroda anyway has its own EvalContext implementation that just calls the Miri methods as fallbacks?

Priroda directly uses miri's EvalContext at the moment.

No code would have to be duplicated, just the signatures, right?

I guess so. I will open an issue on priroda for implementing this.

[RalfJung]

I guess so. I will open an issue on priroda for implementing this.

Okay, so I assume we can land this PR then. :)

@Smittyvb aside from the open comment about the error message, this is ready to land. Thanks a lot for this PR. :)

[RalfJung]

Awesome, and thanks @Smittyvb for you first PR here. :)
@bors r+

[RalfJung]

Hello, bors, are you listening?
@bors r+

[bors]

📌 Commit 8d43d72 has been approved by RalfJung

[bors]

⌛ Testing commit 8d43d72 with merge 0a0e366...

[bors]

☀️ Test successful - checks-actions
Approved by: RalfJung
Pushing 0a0e366 to master...