libco: select the fiber backend on Windows - #12
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On x86_64 the GNU/Clang branch tests __amd64__ before _WIN32 and pulls in amd64.c. Its co_swap executes a machine-code blob stored in a read-only array, which faults under Data Execution Prevention on the first coroutine switch on Windows -- the same failure the MSVC branch already avoids by disabling amd64.c "due to SIGSEGV bug". Check _WIN32 first so Windows targets use the fiber backend (CreateFiber/SwitchToFiber) that MSVC uses, regardless of the compiler (MSVC or MinGW-w64/GCC). Signed-off-by: Jiawei Huang <jiawei@tigera.io>
This was referenced Jul 7, 2026
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On x86_64 the GNU/Clang branch of
libco.ctests__amd64__before_WIN32, so it includesamd64.c. That backend'sco_swapexecutes a machine-code blob held in a read-only array, which faults under Data Execution Prevention on the first coroutine switch on Windows — exactly the failure the MSVC branch already sidesteps by disablingamd64.c"due to SIGSEGV bug" and falling back to fibers.This moves the
_WIN32check ahead of the architecture checks so any Windows target (MSVC or MinGW-w64/GCC) uses thefiber.cbackend (CreateFiber/SwitchToFiber). Non-Windows targets are unaffected; the later_WIN32#elif(previously unreachable on x86_64) is removed.Surfaced while cross-compiling a downstream consumer (fluent-bit) for Windows with the MinGW-w64 toolchain, where GCC defines
__amd64__and the old order silently selected the faulting backend.