This change is adding DWARF (CFI) unwind information to the
hand-written assembly of the
This enables unwinding through the dispatcher from the Linux stack
into (and through) the Windows stack.
The general idea is that the
syscall_frame struct contains the
content of the callee-save registers before the function call
(in particular the stack pointer and the return address). At any
point of the execution, we have a pointer into the
in $rcx, $rbp or $rsp.
For the CFI codes the general idea is that we are defining the
computations of the callee-save registers based on the
syscall_frame using DWARF’s
breg instruction, rather than
relative to CFA.
This change adds a bunch of convenience macros, to (hopefully) improve readability of the CFI instructions.
Note: Those change was used with great success for unwinding through the dispatcher using a modified LLDB shown in the “how-wine-works-101” blog post as well as for in the Orbit profiler, that has mixed-callstack unwinding support.
Test: Inspect callstacks reported by the Orbit profiler while running some Windows targets using the modified wine, as well as verify debugging reports correct callstacks when stepping with our modified LLDB through the dispatcher itself (so that we are able to unwind through the dispatcher at any instruction).