NetBSD Problem Report #60904

From tls@panix.com  Sun Oct 18 21:38:35 2026
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Date: Sun, 18 Oct 2026 17:38:33 -0400 (EDT)
From: tls@panix.com
Reply-To: tls@NetBSD.org
To: gnats-bugs@NetBSD.org
Subject: compiler dumps core cross-building from MacOS on Apple Silicon
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>Number:         60904
>Category:       toolchain
>Synopsis:       compiler dumps core cross-building from MacOS on Apple Silicon
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    toolchain-manager
>State:          needs-pullups
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Oct 18 21:40:01 +0000 2026
>Closed-Date:    
>Last-Modified:  Sun Oct 18 23:07:30 +0000 2026
>Originator:     Thor Lancelot Simon
>Release:        NetBSD 10.0 through NetBSD-current as of 2026-10-18
>Organization:
>Environment:


System: Darwin lungfish.hvg.tjls.com 27.0.0 Darwin Kernel Version 27.0.0: Tue
Aug 11 21:05:42 PDT 2026; root:xnu-13432.1.9~1/RELEASE_ARM64_T6031 arm64
Architecture: arm
Machine: arm64
>Description:
	In highly parallel builds for 64-bit targets (amd64, aarch64) on
	Darwin (MacOS) on Apple Silicon (arm64), NetBSD's cross-gcc segfaults
	while building various files in the in-tree gcc, typically those
	containing "long double" constants.

	The problem is that the GMP in external/lgpl3 has 64-bit ARM ASM
	files that use register x18, which is forbidden by the ABI
	(see https://github.com/ARM-software/abi-aa/blob/7485cc1a1240d9143c6c759390469ae0cbe2d02e/aapcs64/aapcs64.rst#table-2
	and the note immediately below).

	MacOS zeroes this register after a context switch.  If a compilation
	is in one of those GMP routines while the compiler is switched away
	from, x18 will magically change value to 0 and Bad Things will happen.

>How-To-Repeat:
	Get yourself a spiffy new Mac with 28 cores and run
	build.sh -m amd64 -u -U -j28 tools distribution.

>Fix:
	The fix is to avoid use of x18.  It appears GMP did this upstream a
	few years later.

>Release-Note:

>Audit-Trail:

From: "Thor Lancelot Simon" <tls@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/60904 CVS commit: src/tools/gmp
Date: Sun, 18 Oct 2026 23:04:41 +0000

 Module Name:	src
 Committed By:	tls
 Date:		Sun Oct 18 23:04:41 UTC 2026

 Modified Files:
 	src/tools/gmp: Makefile

 Log Message:
 Fix compiler core dumps on MacOS on Apple Silicon (PR toolchain/60904),
 by disabling the use of the broken arm64 asm that comes with the present
 version of GMP (we can re-enable it when we upgrade).


 To generate a diff of this commit:
 cvs rdiff -u -r1.6 -r1.7 src/tools/gmp/Makefile

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

State-Changed-From-To: open->needs-pullups
State-Changed-By: tls@NetBSD.org
State-Changed-When: Sun, 18 Oct 2026 23:07:30 +0000
State-Changed-Why:
Needs pullups to NetBSD-10 and NetBSD-11 which have the broken GMP.


>Unformatted:

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