unix: align Ifreq so its union accessors cannot fault by shalseth · Pull Request #287 · golang/sys

shalseth · 2026-08-23T21:30:09Z

Uint16, SetUint16, Uint32, SetUint32, Inet4Addr and SetInet4Addr cast the
ifreq union to uint16, uint32 or RawSockaddrInet4 and access it in place.
The generated ifreq declares that union as a byte array, so the type
guarantees only byte alignment and the compiler may put an Ifreq at any
address - as it does for the elements of a []Ifreq, which pack at the
struct's size with an alignment of one.

A misaligned access is merely slow on amd64 and arm64; on sparc64 it
faults, and TestIoctlIfreq died with SIGBUS.

Align the wrapper rather than changing the accessors. The union lies at
offset 16 within ifreq on every architecture, so aligning the wrapper
aligns the union, and all six accessors are covered instead of only the
four integer ones.

TestIfreqAlignment pins the invariant. Without the fix it fails on every
architecture, reporting an alignment of 1, so catching a regression does
not need sparc64 hardware.

Updates golang/go#55000

gopherbot · 2026-08-23T21:48:57Z

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gopherbot · 2026-08-23T22:06:10Z

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gopherbot · 2026-08-23T22:06:11Z

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gopherbot · 2026-08-23T22:23:31Z

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Patch Set 2:

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gopherbot · 2026-08-24T05:15:49Z

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Patch Set 2:

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gopherbot · 2026-08-24T08:57:01Z

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gopherbot · 2026-08-24T09:42:40Z

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Patch Set 3:

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gopherbot · 2026-08-24T19:21:24Z

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Patch Set 3: Auto-Submit+1 Code-Review+2 Commit-Queue+1

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gopherbot · 2026-08-24T19:21:25Z

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Patch Set 3:

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gopherbot · 2026-08-24T19:21:25Z

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gopherbot · 2026-08-24T19:21:26Z

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go on master (commit b751a97) / sys on master (change 820000)

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gopherbot · 2026-08-24T19:21:27Z

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Uint16, SetUint16, Uint32, SetUint32, Inet4Addr and SetInet4Addr cast the ifreq union to uint16, uint32 or RawSockaddrInet4 and access it in place. The generated ifreq declares that union as a byte array, so the type guarantees only byte alignment and the compiler may put an Ifreq at any address - as it does for the elements of a []Ifreq, which pack at the struct's size with an alignment of one. A misaligned access is merely slow on amd64 and arm64; on sparc64 it faults, and TestIoctlIfreq died with SIGBUS. Align the wrapper rather than changing the accessors. The union lies at offset 16 within ifreq on every architecture, so aligning the wrapper aligns the union, and all six accessors are covered instead of only the four integer ones. TestIfreqAlignment pins the invariant. Without the fix it fails on every architecture, reporting an alignment of 1, so catching a regression does not need sparc64 hardware. Updates golang/go#55000 Change-Id: I9c5c04515c42702ffec583881b09745f6a52b167

gopherbot · 2026-08-24T19:58:16Z

This PR (HEAD: 637b50d) has been imported to Gerrit for code review.

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gopherbot · 2026-08-24T20:37:54Z

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Patch Set 4:

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gopherbot · 2026-08-25T05:24:01Z

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Patch Set 4: Commit-Queue+1

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gopherbot · 2026-08-25T05:24:01Z

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Patch Set 4:

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gopherbot · 2026-08-25T05:24:02Z

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Patch Set 4: -Commit-Queue

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gopherbot · 2026-08-25T05:24:02Z

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gopherbot · 2026-08-25T05:24:03Z

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gopherbot · 2026-08-25T06:56:05Z

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Patch Set 4: Code-Review+2

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gopherbot · 2026-08-25T12:21:57Z

Message from David Chase:

Patch Set 4: Code-Review+1

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Uint16, SetUint16, Uint32, SetUint32, Inet4Addr and SetInet4Addr cast the ifreq union to uint16, uint32 or RawSockaddrInet4 and access it in place. The generated ifreq declares that union as a byte array, so the type guarantees only byte alignment and the compiler may put an Ifreq at any address - as it does for the elements of a []Ifreq, which pack at the struct's size with an alignment of one. A misaligned access is merely slow on amd64 and arm64; on sparc64 it faults, and TestIoctlIfreq died with SIGBUS. Align the wrapper rather than changing the accessors. The union lies at offset 16 within ifreq on every architecture, so aligning the wrapper aligns the union, and all six accessors are covered instead of only the four integer ones. TestIfreqAlignment pins the invariant. Without the fix it fails on every architecture, reporting an alignment of 1, so catching a regression does not need sparc64 hardware. Updates golang/go#55000 Change-Id: I70aca33419086de9eb68032e354e5f666cc20562 GitHub-Last-Rev: 637b50d GitHub-Pull-Request: #287 Reviewed-on: https://go-review.googlesource.com/c/sys/+/820000 Reviewed-by: Ian Lance Taylor <iant@golang.org> Reviewed-by: David Chase <drchase@google.com> LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Cherry Mui <cherryyz@google.com>

gopherbot · 2026-08-25T14:37:08Z

This PR is being closed because golang.org/cl/820000 has been merged.

shalseth force-pushed the sparc64-ifreq branch from 658c19c to 2a96d26 Compare August 24, 2026 08:48

shalseth changed the title ~~unix: avoid unaligned loads in the Ifreq union accessors~~ unix: align Ifreq so its union accessors cannot fault Aug 24, 2026

shalseth force-pushed the sparc64-ifreq branch from 2a96d26 to 1879a16 Compare August 24, 2026 08:56

shalseth force-pushed the sparc64-ifreq branch from 1879a16 to 637b50d Compare August 24, 2026 19:57

gopherbot closed this Aug 25, 2026

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