proc/native: surface FlushInstructionCache failures on Windows - #4413
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proc/native: surface FlushInstructionCache failures on Windows#4413derekparker wants to merge 2 commits into
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Previously flush errors were ignored, which made I-cache coherency problems on windows/arm64 hard to diagnose. Return and log the error so a failed flush fails the write instead of looking like a missed breakpoint.
aarzilli
reviewed
Aug 6, 2026
| // breakpoints or execute the wrong instruction after a patch. | ||
| if err := _FlushInstructionCache(t.dbp.os.hProcess, uintptr(addr), count); err != nil { | ||
| err = fmt.Errorf("FlushInstructionCache(%#x, %d): %w", addr, count, err) | ||
| logflags.DebuggerLogger().Errorf("%v", err) |
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Why both logging and returning?
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I know it's redundant, but I wanted to throw everything at it and see if anything is discoverable by CI (maybe the error gets swallowed or something). Kind of grasping at straws here honestly trying to figure out these seemingly never-ending windows/arm64 flakes.
When we pass an exception through to the debuggee (or see a
breakpoint trap whose memory is not our BRK), dump ExceptionCode,
address, and ExceptionInformation so CI can distinguish access
violations from illegal instructions behind throw("fault").
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Summary
Stop swallowing FlushInstructionCache errors after WriteProcessMemory. If the flush fails, return the error so it shows up instead of looking like a missed breakpoint.
Part of digging into flaky TestNextWhileNexting / TestStepShadowConcurrentBreakpoint on windows/arm64 with Go 1.27.