net: fix MIB_IF_ROW2 layout on Windows 386 - #2120
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shirou
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Thanks for tracking this down — the analysis is correct, and I verified that TransmitLinkSpeed lands at offset 1192 with a total size of 1352 on 386 with this padding, matching amd64.
One suggestion: since unsafe.Alignof is a constant expression and net_windows.go already imports unsafe, the padding can be derived directly, without the two build-tagged files:
const (
maxStringSize = 256
maxPhysAddressLength = 32
// Windows aligns ULONG64 to 8 bytes, but Go only gives uint64 4-byte
// alignment on 32-bit architectures, so pad ConnectionType up to the
// next 8-byte boundary there.
// https://learn.microsoft.com/en-us/windows/win32/api/netioapi/ns-netioapi-mib_if_row2
pad0for64_4for32 = (8 - unsafe.Alignof(uint64(0))) % 8
)This yields 4 on windows/386 and 0 on windows/amd64 and windows/arm64 (same as today), and it also stays correct for any other 32-bit Windows port, which !386 would miss.
Would you mind giving it a try?
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Fixes #1865.
Windows aligns the
ULONG64fields inMIB_IF_ROW2to an 8-byte boundary. Go only givesuint644-byte alignment on 386, which causedTransmitLinkSpeedand every following network counter to be read four bytes early.This adds four bytes of explicit padding for Windows 386 while retaining the existing layout on other Windows architectures. A deterministic 386 regression test verifies the
TransmitLinkSpeedoffset and total structure size.Verification
go test ./net -count=1with CI behavior enabledgit diff --checkAI disclosure
OpenCode using
myself/gpt-5.6-solassisted with issue investigation, implementation, and test preparation. I reviewed the ABI rationale, source changes, and verification results.