cmd/link: inconsistent argument order in hostLink() and linkerFlagSupported()

[voxeljorge]

Go version

1.23.2

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/jorge/.cache/go-build'
GOENV='/home/jorge/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/jorge/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/jorge/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/home/jorge/.cache/bazel/_bazel_jorge/576ee54cf2522471c5c073f98825487b/external/go_sdk'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/home/jorge/.cache/bazel/_bazel_jorge/576ee54cf2522471c5c073f98825487b/external/go_sdk/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.23.2'
GODEBUG=''
GOTELEMETRY='local'
GOTELEMETRYDIR='/home/jorge/.config/go/telemetry'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/home/jorge/Projects/voxel/go.mod'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build758936887=/tmp/go-build -gno-record-gcc-switches'

What did you do?

Attempted to link programs using a hermetic llvm toolchain and sysroot with go tool link.

Reproducing this is a little difficult as the conditions for this bug surfaced through a Bazel build using the rules_go ruleset: bazel-contrib/rules_go#3886

What did you see happen?

Calls to go tool link detected all linker flags as unsupported, causing go tool link to add flags like -rdynamic when static linking: https://cs.opensource.google/go/go/+/master:src/cmd/link/internal/ld/lib.go;l=1732?q=hostlink

In my case this caused hostLink() to fail with PIE errors when static linking, although I'm sure other errors related to flag ordering are possible.

What did you expect to see?

I expected to see programs link correctly. They in fact did link correctly when no sysroot was used but failed to do so when using a sysroot. Triggering and analyzing this bug was challenging due to the fact that there seems to be no logging that can be turned on for linkerFlagSupported(). This was encountered while building Go code with Bazel using rules_go and fix for the rules_go side of this issue has been proposed here: bazel-contrib/rules_go#4144

The cause of the rules_go bug appears to be an inconsistency in how go tool link calls linkers from linkerFlagSupported() and hostLink() which could affect users more generally than just in rules_go

Calls to linkerFlagSupported() put any -extldflags that were specified before the cgo flags that have been extracted from archives, while hostLink() seems to put them after. In cases where the archives were originally built with a --sysroot parameter which needs to be adjusted (because maybe the archives were built in a different sandbox than the final program for example) this means that linkerFlagSupported() is likely to detect all linker flags as "unsupported". The sysroot parameter specified in -extldflags will basically be ignored for linkerFlagSupported() calls but not for hostLink() calls.

I suspect this is just an oversight and not intended behavior. A simple fix would just be to adjust linkerFlagSupported() to always put -extldflags at the end.

[gabyhelp]

Related Issues and Documentation

• cmd/link: wrong flag order when checking supported linker flags #69350
• cmd/link: relative paths are not respected when checking supported linker flags #59952 (closed)
• cmd/link: regression in handling of linker flags #16842 (closed)
• cmd/go,cmd/link: prefer external linking when strange cgo flags seen
• cmd/link: fix checks for supported linker flags with relative paths.
• cmd/go: TestScripts fail when glibc is included with FLAGS #50985 (closed)
• cmd/link: doesn't propagate -I flags to the external linker #22446 (closed)
• cmd/go/internal/load: -ldflags should be included in buildinfo when -trimpath is set and CGO_ENABLED=0 #63558 (closed)
• cmd/go: allow flags in CGO_LDFLAGS environment variable not in security allowlist #42565 (closed)
• cmd/link: check CGO_CFLAGS for non -g/-I/-O options before internal linking

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

[voxeljorge]

ah I see my search failed, as this is is a duplicate of #69350