PR/60812 CVS commit: src/sys/kern

["Taylor R Campbell" <riastradh%netbsd.org@localhost>]

The following reply was made to PR port-evbmips/60812; it has been noted by GNATS.

From: "Taylor R Campbell" <riastradh%netbsd.org@localhost>
To: gnats-bugs%gnats.NetBSD.org@localhost
Cc: 
Subject: PR/60812 CVS commit: src/sys/kern
Date: Sun, 27 Sep 2026 22:00:33 +0000

 Module Name:	src
 Committed By:	riastradh
 Date:		Sun Sep 27 22:00:33 UTC 2026
 
 Modified Files:
 	src/sys/kern: kern_proc.c
 
 Log Message:
 proc(9): Allocate struct proc with declared alignment.
 
 The definition of struct proc includes __aligned(COHERENCY_UNIT) on
 the p_auxlock member, so the compiler will assume struct proc
 pointers are aligned as such.
 
 As a space optimization on uniprocessor systems, we define the
 variable `coherency_unit' (as part of the module ABI) to be
 COHERENCY_UNIT (often 64 or 128) in MULTIPROCESSOR builds, but
 toALIGNBYTES+1 (often 4, 8, or 16) for !MULTIPROCESSOR builds where
 cache line sharing isn't as much of a problem.
 
 But this isn't safe as an optimization for allocating objects that
 have statically declared (as part of their ABI) COHERENCY_UNIT
 alignment.
 
 PR port-evbmips/60812: UBSan: Undefined Behavior in [sys-src]  member
 access within misaligned address  [..] for type '[..]' which requires
 128 byte alignment
 
 
 To generate a diff of this commit:
 cvs rdiff -u -r1.286 -r1.287 src/sys/kern/kern_proc.c
 
 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.