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Since Cygwin 3.4.0 the Cygwin DLL is linked with --dynamicbase and the runtime can "run with full ASLR enabled" (943433b, "Cygwin: Enable dynamicbase on the Cygwin DLL by default"). MSYS2 reverts that linker flag ("Revert 'Cygwin: Enable dynamicbase on the Cygwin DLL by default'") because fork() started failing inside Docker containers, see https://cygwin.com/pipermail/cygwin/2022-December/252711.html; that failure was never diagnosed and the revert still stands. As a consequence, msys-2.0.dll carries no dynamicbase flag, and when "Force randomization for images (Mandatory ASLR)" is enabled in Windows Security's Exploit protection, Windows relocates it in every process. The forked child then runs the DLL at a different address than its parent, which fork emulation cannot survive. All the user gets after the retries are exhausted is dofork: child -1 - forked process 50032 died unexpectedly, retry 0, exit code 0xC0000142, errno 11 followed by the shell's "fork: retry: Resource temporarily unavailable". Nothing in that output points at the cause, so users keep reporting it as a bug in the runtime or in the programs built on it (e.g. msys2#327, git-for-windows/git#1412), and the usual answer, to exempt the executables from the setting or to turn it off, never reaches the people who hit it in CI logs or behind a GUI. Windows reports the effective policy of the current process via GetProcessMitigationPolicy(); EnableForceRelocateImages is set exactly when the system-wide setting is on and this executable has not been exempted. When that is the case and fork() fails, print one extra line, once per process, naming the cause, the affected executable, and where the exemption is configured. Processes not subject to the setting see no change. This is deliberately not submitted to Cygwin: upstream supports Mandatory ASLR, so the condition only exists in the MSYS2 build. The real fix would be to drop the dynamicbase revert once the Docker failure is understood; until then, this is the stopgap. Addresses: msys2#327 Assisted-by: Claude Fable 5.1 Signed-off-by: Ali Robertson <[email protected]>
This was referenced Oct 7, 2026
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Please consider #381 instead. It restores the
--dynamicbaselink flag so this failure no longer happens; this PR is only the fallback if #381 is declined.Under Windows' Mandatory ASLR ("Force randomization for images"), every MSYS program fails to fork with only
forked process ... died unexpectedly, ... exit code 0xC0000142. This adds one line to that error, printed once per process and only whenGetProcessMitigationPolicy()reports forced relocation for the current executable:Tested with the CI-built DLL on Windows 11: the line appears for an unexempted executable and not for an exempted one.
Addresses #327, git-for-windows/git#1412.
Assisted by Claude Fable 5.1; reviewed, tested and signed off by the author.