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feat: a run cut short on a TTD replay is put back where it started - #202
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TTD does not leave an interrupted replay where it had got to. It prints "the current position is approximately how far we had gone" and then, measured, usually moves it to the trace's end - past every breakpoint the run had not reached, with no hit reported - and now and then to a breakpoint itself, again with no hit (windbg-mcp item 125). A caller reading that stop as progress concludes the breakpoint is never hit. execute_and_wait, settle and run_to_address now read the position before the run, through the debugger data model, and when a deadline or a host's break cuts the run short they SeekTo back to it and read the position and current thread again to confirm. CommandRun::replay and RunToResult::replay carry the outcome as a ReplayLanding. ttd_position is public and typed (TtdPosition), and DebuggeeType::is_ttd_replay gates it: a .run opened by open_trace reports qualifier DEBUG_USER_WINDOWS_IDNA, not a dump qualifier, so a live target pays one GetDebuggeeType per resume and never touches the data model. examples/ttd_position_probe.rs holds the measurements (x64, two traces, every bounded run put back and every following g reaching the breakpoint). Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01H84hv8GzUbK25UnnEC6eSb
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What changes
TTD does not leave an interrupted replay where it had got to. It prints "the current position is approximately how far we had gone" and then moves it somewhere of its own choosing. Measured, that is usually the trace's end, past every breakpoint the run had not reached, with no hit reported. Now and then it is a breakpoint itself, again with no hit. A caller reading that stop as progress concludes the breakpoint is never hit (windbg-mcp item 125).
execute_and_wait,settleandrun_to_addressput a cut-short replay back. Each reads the position before the run, through the debugger data model (@$curthread.TTD.Position). When a deadline or a host's break cuts the run short, it calls that position object's ownSeekTo, then reads the position and current thread again to confirm.CommandRun::replay/RunToResult::replaycarry the outcome as aReplayLanding:Rewound { to }, orNotRewound { from, left_at }when the travel back failed. They areNoneon every other target.DebugEngine::ttd_positionis public and typed (TtdPosition { sequence, steps }, ordered as the trace is,Displayas!ttreads it).DebuggeeType::is_ttd_replayis the gate. A.runopened byopen_tracereports class 2, qualifier 2 (DEBUG_USER_WINDOWS_IDNA), not a dump qualifier. So a live target pays oneGetDebuggeeTypeper resume and never touches the data model.windowsgainsWin32_System_Com,Win32_System_OleandWin32_System_Variant, whichIModelObject::GetIntrinsicValueis gated on.Breaking:
CommandRunandRunToResultgain a public field. Struct literals addreplay: None(noted in the CHANGELOG's migration section).Measured
examples/ttd_position_probe.rs, x64 host,dbgeng10.0.29547.1002, TTD 1.11.617.0, against two unindexed traces (hostname.exe28 MiB,cmd.exe /c for /L …48 MiB), with a breakpoint onntdll!RtlExitUserProcess.g-settlerun_to_addressAfter every put-back, the next
gstopped at the breakpoint. The seek takes about 1.5 ms and leaves the engine atDEBUG_STATUS_BREAKwith nothing to pump. An ordinary user dump answersttd_position() == None.Tests
cargo test --lib: 469 passed, 13 ignored.test_a_replay_is_the_idna_qualifier_on_a_user_targettest_a_ttd_position_orders_by_sequence_then_steps_and_prints_as_tt_reads_ittest_a_live_target_is_no_replay_and_is_not_put_back, which runs all three bounded paths on a launched process.is_ttd_replayanswer true for any user target fails both of the gate tests.Rewoundwithout seeking fails that tier with the stop left at the end-of-trace IP.cargo clippy --all-targets -D warningsreports ten findings, all in code this PR does not touch (newer toolchain lints). CI does not run clippy here.The new code is FFI (
VariantClear, anAddRef'dpunkValclone), so Miri, which does not run on PRs, has nothing new it can reach.🤖 Generated with Claude Code
https://claude.ai/code/session_01H84hv8GzUbK25UnnEC6eSb