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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X-From4GNATS: "tls@panix.com via gnats" <gnats-admin@NetBSD.org>

>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:          closed
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Oct 18 21:40:01 +0000 2026
>Closed-Date:    Sun Nov 01 03:40:26 +0000 2026
>Last-Modified:  Sun Nov 01 03:40:26 +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.


From: GOVIND PANDEY <govindup63@gmail.com>
To: gnats-bugs@netbsd.org
Cc: 
Subject: Re: toolchain/60904: compiler dumps core cross-building from MacOS on
 Apple Silicon
Date: Sun, 18 Oct 2026 20:53:12 -0400

 --00000000000051f966065e26f0c2
 Content-Type: text/plain; charset="UTF-8"

 Hi,

 I can confirm both the problem and the fix on the netbsd-11 branch, in
 case it helps with the pullup.

 Host: Darwin 27.0.0 arm64, Apple M4 (MacBook Air, 10 cores)
 Tree: netbsd-11 from the git mirror, 36cf5108d (2026-10-14)
 Build: ./build.sh -U -u -m amd64 -j10 tools

 With tools/gmp/Makefile at 1.6 (so assembly enabled on arm64, GMP 6.2.1
 with ten mpn/arm64/*.asm files that use x18), I took the resulting
 x86_64--netbsd-gcc and compiled a 300-line C file of long double
 constant expressions 600 times, 24 in parallel. 62 of them died:

 44 internal compiler error: Segmentation fault: 11
 27 internal compiler error: Bus error: 10
 6 internal compiler error: Abort trap: 6
 1 internal compiler error: Trace/BPT trap: 5

 (some runs printed two signatures, hence the total over 62.)

 I then applied the 1.6 -> 1.7 change to tools/gmp/Makefile, which
 applies cleanly with patch -p1 since the branch copy is identical to
 HEAD at 1.6, removed the gmp, mpfr, mpc and gcc objects and rebuilt
 tools. GMP's config.status now shows --disable-assembly and nothing
 under mpn/ is built from .asm. The same stress run, done twice:

 600 compiles, 24 parallel, 0 failures
 600 compiles, 24 parallel, 0 failures

 I haven't tried netbsd-10, mostly because I'm short on disk for a
 second tree.

 Thanks,
 Govind Pandey

 --00000000000051f966065e26f0c2
 Content-Type: text/html; charset="UTF-8"
 Content-Transfer-Encoding: quoted-printable

 <html><body><div dir=3D"auto">Hi,<br><br>I can confirm both the problem and=
  the fix on the netbsd-11 branch, in<br>case it helps with the pullup.<br><=
 br>Host: Darwin 27.0.0 arm64, Apple M4 (MacBook Air, 10 cores)<br>Tree: net=
 bsd-11 from the git mirror, 36cf5108d (2026-10-14)<br>Build: ./build.sh -U =
 -u -m amd64 -j10 tools<br><br>With tools/gmp/Makefile at 1.6 (so assembly e=
 nabled on arm64, GMP 6.2.1<br>with ten mpn/arm64/*.asm files that use x18),=
  I took the resulting<br>x86_64--netbsd-gcc and compiled a 300-line C file =
 of long double<br>constant expressions 600 times, 24 in parallel. 62 of the=
 m died:<br><br>  44 internal compiler error: Segmentation fault: 11<br>  27=
  internal compiler error: Bus error: 10<br>   6 internal compiler error: Ab=
 ort trap: 6<br>   1 internal compiler error: Trace/BPT trap: 5<br><br>(some=
  runs printed two signatures, hence the total over 62.)<br><br>I then appli=
 ed the 1.6 -&gt; 1.7 change to tools/gmp/Makefile, which<br>applies cleanly=
  with patch -p1 since the branch copy is identical to<br>HEAD at 1.6, remov=
 ed the gmp, mpfr, mpc and gcc objects and rebuilt<br>tools. GMP&#39;s confi=
 g.status now shows --disable-assembly and nothing<br>under mpn/ is built fr=
 om .asm. The same stress run, done twice:<br><br>  600 compiles, 24 paralle=
 l, 0 failures<br>  600 compiles, 24 parallel, 0 failures<br><br>I haven&#39=
 ;t tried netbsd-10, mostly because I&#39;m short on disk for a<br>second tr=
 ee.<br><br>Thanks,<br>Govind Pandey<br></div></body></html>

 --00000000000051f966065e26f0c2--

From: "Martin Husemann" <martin@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/60904 CVS commit: [netbsd-11] src/tools/gmp
Date: Tue, 20 Oct 2026 19:01:29 +0000

 Module Name:	src
 Committed By:	martin
 Date:		Tue Oct 20 19:01:29 UTC 2026

 Modified Files:
 	src/tools/gmp [netbsd-11]: Makefile

 Log Message:
 Pull up following revision(s) (requested by tls in ticket #533):

 	tools/gmp/Makefile: revision 1.7

 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 -r1.6.2.1 src/tools/gmp/Makefile

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

From: "Martin Husemann" <martin@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/60904 CVS commit: [netbsd-10] src/tools/gmp
Date: Tue, 20 Oct 2026 19:02:33 +0000

 Module Name:	src
 Committed By:	martin
 Date:		Tue Oct 20 19:02:33 UTC 2026

 Modified Files:
 	src/tools/gmp [netbsd-10]: Makefile

 Log Message:
 Pull up following revision(s) (requested by tls in ticket #1366):

 	tools/gmp/Makefile: revision 1.7

 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 -r1.5.2.1 -r1.5.2.2 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: needs-pullups->closed
State-Changed-By: dholland@NetBSD.org
State-Changed-When: Sun, 01 Nov 2026 03:40:26 +0000
State-Changed-Why:
pullups complete


>Unformatted:

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