cmd/go: build sets PWD to relative path

[trofi]

What version of Go are you using (go version)?

$ go version
go version go1.16.5 linux/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE=""

GOARCH="amd64"

GOBIN=""

GOCACHE="/home/slyfox/.cache/go-build"

GOENV="/home/slyfox/.config/go/env"

GOEXE=""

GOFLAGS=""

GOHOSTARCH="amd64"

GOHOSTOS="linux"

GOINSECURE=""

GOMODCACHE="/home/slyfox/go/pkg/mod"

GONOPROXY=""

GONOSUMDB=""

GOOS="linux"

GOPATH="/home/slyfox/go"

GOPRIVATE=""

GOPROXY="https://proxy.golang.org,direct"

GOROOT="/usr/lib/go"

GOSUMDB="sum.golang.org"

GOTMPDIR=""

GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"

GOVCS=""

GOVERSION="go1.16.5"

GCCGO="gccgo"

AR="ar"

CC="x86_64-pc-linux-gnu-gcc"

CXX="x86_64-pc-linux-gnu-g++"

CGO_ENABLED="1"

GOMOD="/dev/null"

CGO_CFLAGS="-g -O2"

CGO_CPPFLAGS=""

CGO_CXXFLAGS="-g -O2"

CGO_FFLAGS="-g -O2"

CGO_LDFLAGS="-g -O2"

PKG_CONFIG="pkg-config"

GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build2541492012=/tmp/go-build -gno-record-gcc-switches"

What did you do?

This is a forward of downstream ccache/ccache#860 bug where ccache was confused by PWD=. set by go build. In ccache/ccache#860 (comment) Joel Rosdahl notes that PWD should be an absolute path.

ccache is fixed since but I think it's worth fixing go build not to produce relative paths.

Executable single-file example:

Here is a directly executable example to illustrate the problem extracted from docker project:

#!/bin/bash

CC=gcc

# cleanup
rm -rf -- temp bug ccache-wrappers .cache

# create test files:
## simple go.mod:
cat > go.mod <<EOF
module github.com/PWD-bug

go 1.13
EOF

## simple main.go:
cat > main.go <<EOF
package main

import "C"

func main() {}
EOF

# create local ccache wrapper for $CC
mkdir -p ccache-wrappers
ln -s /usr/bin/ccache ccache-wrappers/${CC}

# create temp dir
mkdir -p temp

env -i \
  "CC=$CC" \
  "HOME=$(pwd)" \
  "TMPDIR=$(pwd)/temp" \
  "CCACHE_BASEDIR=$(pwd)" \
  "PATH=$(pwd)/ccache-wrappers:/usr/bin:/bin" \
go build -o bug .

What did you expect to see?

Expected the test to build successfully.

What did you see instead?

The ccache detects relative path in PWD and crashes:

$ ./bug.bash
# github.com/PWD-bug
/usr/lib/go/pkg/tool/linux_amd64/link: running gcc failed: signal: aborted (core dumped)
ccache: Util.cpp:731: std::string Util::get_relative_path(nonstd::sv_lite::string_view, nonstd::sv_lite::string_view): failed assertion: Util::is_absolute_path(dir)

[seankhliao]

cc @bcmills @jayconrod @matloob

[jayconrod]

Looked into this a bit. I was able to reproduce the failure on a Debian machine. Adding a panic on non-absolute paths to base.AppendPWD caused problems very quickly. There are cases where we pass in "" and ".".

[gopherbot]

Change https://golang.org/cl/378396 mentions this issue: cmd/go/internal/base: in AppendPWD, check that PWD is absolute

[gopherbot]

This issue is currently labeled as early-in-cycle for Go 1.19.
That time is now, so a friendly reminder to look at it again.