[Lldb-commits] [PATCH] D109777: [lldb] [Windows] Fix continuing from breakpoints and singlestepping on ARM/AArch64

Wed Sep 15 04:36:47 PDT 2021

mstorsjo added a comment.

In D109777#3001429 <https://reviews.llvm.org/D109777#3001429>, @DavidSpickett wrote:

> https://docs.microsoft.com/en-us/cpp/intrinsics/debugbreak?view=msvc-160 confirms the AArch64 breakpoint instruction, were you able to find a source for the Arm/Thumb one?

I don't have a formal source for that one, but compiling a `__debugbreak()` with MSVC produces that opcode. As Windows is thumb-only, we can always do a breakpoint with that single opcode (even if the targeted instruction happens to be a wide thumb2 instruction) without needing to detect betwen arm/thumb mode.

> Otherwise the logic seems fine. It would be good to dedupe these switches, in a file in `Plugins/Process/Windows/Common/`?
> Or move some of this into the register context? Assuming you have access to a register context in all of these places. It's a bit weird to put it there since the only register related thing is the single step bit but that's the only per architecture class at the moment.

You mean the duplication between the "native" and regular versions of the classes - or the arch specific switches in otherwise seemingly arch-independent code?

(In case it's not familiar to all - the former duplication is because lldb can operate in two modes - either with lldb directly controlling the debugged process (which is the case without the "native" prefix) or with lldb spawning lldb-server which then owns the debugged process (the classes with the "native" prefix).)

For the former, I'm not quite familiar enough the how the architecture of these things work in practice, but I think those two class hiearchies/families don't have much in common, so there's no immediate common place to put shared code between the two.

For the latter - I guess it'd maybe be possible to add some extra locally defined (not overriding a virtual method from the base classes) methods in the register contexts that return the breakpoint opcodes, their sizes and the right flag bits...

> (also all the Windows code being in `Windows/Common` is odd but ok not a thing for now)

Yeah that's a bit odd indeed. There's also a few other oddities in the lldb tree, like some directiories being capitalized while others aren't, I guess it's one of the many cases where it's just not worth the churn to change it.

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https://reviews.llvm.org/D109777