Differential D54920

STACKALIGN: Reimplement in terms of __align_down
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Authored by jhb on Jan 27 2026, 10:29 PM.

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brooks
kib
andrew
manu

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rGe9a697bf20cc: STACKALIGN: Reimplement in terms of __align_down

Summary

This changes STACKALIGN to be type-preserving when operating on
pointers.

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Repository

rG FreeBSD src repository

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Build Status

Buildable 70173
Build 67056: arc lint + arc unit

Event Timeline

jhb created this revision.Jan 27 2026, 10:29 PM

Herald added a reviewer: andrew. · View Herald TranscriptJan 27 2026, 10:29 PM

Herald added a reviewer: andrew. · View Herald Transcript

Herald added a reviewer: manu. · View Herald Transcript

Herald added subscribers: riscv, emaste, imp. · View Herald Transcript

jhb requested review of this revision.Jan 27 2026, 10:29 PM

Harbormaster completed remote builds in B70173: Diff 170616.Jan 27 2026, 10:29 PM

kib added inline comments.Jan 27 2026, 10:44 PM

sys/arm/include/param.h
50	Why STACKALIGN needs to be MD then? It is enough to have STACKALIGNBYTES defined in machine/param.h. And please add a comment that it is type-preserving.

Effort: CHERI upstreaming or whatever it is seems like it would apply?

brooks accepted this revision.Jan 28 2026, 10:12 AM

brooks added inline comments.

sys/arm/include/param.h
50	It's only defined on arm/riscv. STACKALIGNBYTES should surely be STACKALIGN_MASK or the like, but that's a different change.

This revision is now accepted and ready to land.Jan 28 2026, 10:12 AM

kib added inline comments.Jan 28 2026, 10:16 AM

sys/arm/include/param.h
50	It's only defined on arm/riscv. Yes, this is why I said that it is enough to have STACKALIGNBYTES in machine/param.h. sys/param.h could then do #ifdef STACKALIGNBYTES #define STACKALIGN ... #endif and it would be immediately have uses at least on amd64 where we align stack after the signal frame. Might be for i386 too, but I do not remember.

jhb added inline comments.Jan 28 2026, 11:52 PM

sys/arm/include/param.h
50	I would be happy to move it. I do think it would be nicer on other arches as well. I do wish the STACKALIGNBYTES wasn't the biased value. I'm not sure if we expose this to userland though. :( Let me see if it's feasible to change that to the unbiased value.

Centralize STACKALIGN and pass tinderbox

This revision now requires review to proceed.Feb 5 2026, 6:38 PM

Harbormaster completed remote builds in B70443: Diff 171274.Feb 5 2026, 6:39 PM

There are opportunities with amd64 at least, but I can do it myself after this patch lands. Thanks.

This revision is now accepted and ready to land.Feb 5 2026, 6:42 PM

brooks accepted this revision.Feb 6 2026, 9:13 AM

Closed by commit rGe9a697bf20cc: STACKALIGN: Reimplement in terms of __align_down (authored by jhb). · Explain WhyFeb 6 2026, 3:31 PM

This revision was automatically updated to reflect the committed changes.

jhb added a commit: rGe9a697bf20cc: STACKALIGN: Reimplement in terms of __align_down.

Revision Contents
Changeset List

Path

Size

sys/

arm/

arm/

2 lines

4 lines

include/

2 lines

arm64/

arm64/

2 lines

2 lines

include/

2 lines

linux/

2 lines

riscv/

include/

2 lines

riscv/

2 lines

Diff 170616

sys/arm/arm/machdep.c

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sys/arm/arm/vm_machdep.c

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sys/arm/include/param.h

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sys/arm64/arm64/exec_machdep.c

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sys/arm64/arm64/vm_machdep.c

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sys/arm64/include/param.h

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sys/arm64/linux/linux_sysvec.c

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sys/riscv/include/param.h

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sys/riscv/riscv/exec_machdep.c

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