[cpu] support TF single-stepping to make gdb work#1574
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The trap flag (
FLAG_TRAP) was previously logged as unsupported and cleared onupdate_eflags, so any guest debugger relying on single-stepping didn't work.This adds proper TF handling: when TF is set,
cycle_internalinterprets one instruction at a time and raises #DB afterwards. DR6.BS is set so the guest can distinguish a single-step trap from a hardware breakpoint.With this, gdb breakpoints and single-stepping (stepi/continue over breakpoints) now work inside the guest.
Fixes #278.