WallisSkillandClaude Opus 5.5 8aafe2440d fix(libkernel): take a return breakpoint hit that a disarm cleared under it ...

A raise delivered some other way (the deliverer sampled the target in guest
code and redirected it) disarms the return breakpoint by clearing DR0 and
DR7 with SetThreadContext. When the target reaches the armed return address
at the same moment, the debug exception is already raised but the context
Windows hands to the handler carries the cleared registers: DR0, DR6 and DR7
are 0. ReturnBreakHandler required DR6.B0, so it declined, and the unhandled
EXCEPTION_SINGLE_STEP ended the process with 0x80000004. Under parallel load
guest_raise_in_host_code failed this way 18 times in 900 runs; a diagnostic
in the declining branch showed every failure at an address armed earlier on
that same thread, with no live return break, DR0 = DR6 = DR7 = 0 and TF
clear.

The ring of armed addresses now records the thread with each address. A
single-step that has TF clear, no breakpoint hit in DR6 and no breakpoint
enabled in DR7, at an address this library armed on the faulting thread, is
taken as that disarmed return breakpoint and continues; any other
single-step is left to the next handler. A DR0 hit is likewise matched
against the addresses armed on the faulting thread.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

2026-10-26 19:43:00 +07:00

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include

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src

fix(libkernel): take a return breakpoint hit that a disarm cleared under it

2026-10-26 19:43:00 +07:00