cmd/go/internal/work: wrong arch detection for s390x

[taronaeo]

Go version

go version devel go1.25-5eaeb7b455 Thu Apr 3 15:36:36 2025 -0700 linux/s390x

Output of go env in your module/workspace:

AR='ar'                                                                                                                             
CC='gcc'                                                                                                                            
CGO_CFLAGS='-O2 -g'                                                                                                                 
CGO_CPPFLAGS=''                                                                                                                     
CGO_CXXFLAGS='-O2 -g'                                                                                                               
CGO_ENABLED='1'                                                                                                                     
CGO_FFLAGS='-O2 -g'                                                                                                                 
CGO_LDFLAGS='-O2 -g'                                                                                                                
CXX='g++'                                                                                                                           
GCCGO='/usr/bin/gccgo'                                                                                                              
GO111MODULE=''                                                                                                                      
GOARCH='s390x'                                                                                                                      
GOAUTH='netrc'                                                                                                                      
GOBIN=''
GOCACHE='/root/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/root/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -march=z196 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build1226758756=/tmp/go-build -gno-record-gcc-switches' 
GOHOSTARCH='s390x'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/opt/ollama/go.mod'
GOMODCACHE='/root/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/root/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/opt/goroot'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/root/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/opt/goroot/pkg/tool/linux_s390x'
GOVCS=''
GOVERSION='devel go1.25-5eaeb7b455 Thu Apr 3 15:36:36 2025 -0700'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

I'm trying to compile Ollama with -march=z15 -mtune=z15 -mvx -mzvector but runtime/cgo is reporting that hardware vector support is not available on z196 while my actual machine is z15.

$ uname -a
Linux aitest 5.14.0-575.el9.s390x #1 SMP Tue Mar 25 17:28:06 UTC 2025 s390x s390x s390x GNU/Linux

$ CGO_CPPFLAGS="-I/opt/openblas-libs/include" CGO_LDFLAGS="-L/opt/openblas-libs/lib -lopenblas" CC="gcc -march=z15 -mtune=z15 -mvx -mzvector" go run . serve

# runtime/cgo
cc1: error: hardware vector support not available on z196

Running a check on the environment variables reported that the machine type is indeed enforced as z196, which is incorrect.

$ go env | grep GOGCCFLAGS
GOGCCFLAGS='-fPIC -m64 -march=z196 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build2459717027=/tmp/go-build -gno-record-gcc-switches'

Trying to override the GOGCCFLAGS was met with go: GOGCCFLAGS cannot be modified as follows

$ go env -w GOGCCFLAGS="-fPIC -m64 -march=z15 -mtune=z15 -mvx -mzvector -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build2459717027=/tmp/go-build -gno-record-gcc-switches"
go: GOGCCFLAGS cannot be modified

What did you see happen?

My Ollama development project fails to compile with -march=z15 -mtune=z15 -mvx -mzvector because the machine type is enforced to z196 which is incorrect.

What did you expect to see?

I was expecting Go to use the correct machine type i.e., z15 = -march=z15, z16 = -march=z16 instead of defaulting to -march=z196 which is very old. Otherwise, a possible method of overriding the GOGCCFLAGS to fix this bug.

[gabyhelp]

Related Issues

• x/image/vector TestMakeFlInXxx fails on s390x and ppc64le #21460 (closed)
• x/crypto/sha3: When compiling for all platforms `undefined: cpu.S390X` #31227 (closed)
• cmd/compile: illegal instruction on s390x #16637 (closed)
• cmd/go: TestCgoConsistentResults fails on s390x with gcc 6 #16780 (closed)
• cmd/compile: linux/s390x: inlining bug in s390x #64468 (closed)

Related Code Changes

• runtime: handle SIGPE exception for p256 crypto package on s390x

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[seankhliao]

I believe it comes from https://go.googlesource.com/go/+/ba7b8ca336123017e43a2ab3310fd4a82122ef9d/src/cmd/go/internal/work/exec.go#2590

[taronaeo]

Hi @seankhliao, thanks for quickly triaging this issue! Yep, it appears to be coming from there.

By any chance can we add conditional detection, otherwise default to -march=native instead of using -march=z196?

Edit: I think with conditional detection, we should also be able to turn on specific hardware support i.e., -mvx -mzvector for z15. Maybe a reference to src/runtime/os_linux_s390x.go?

[taronaeo]

I have temporarily patched Golang on my side and have verified that the referenced file is causing the problem. Please let me know if the Golang team is looking into a patch or if I should try and make one on my own, and create a PR :)

[mknyszek]

CC @golang/s390x

[mknyszek]

I think a patch would be welcome, but it would be good to get feedback from the s390x maintainers.