cmd/cgo: enabling optimizations breaks cgo

[dominikh]

Please answer these questions before submitting your issue. Thanks!

1. What version of Go are you using (go version)?
   go version go1.6 linux/amd64

2. What operating system and processor architecture are you using (go env)?
   GOHOSTARCH="amd64"
   GOHOSTOS="linux"

3. What did you do?
   (Use play.golang.org to provide a runnable example, if possible.)

   bug.go: http://play.golang.org/p/buelTjtxyA

   $ go build bug.go
   $ CGO_CFLAGS="-O0" go build bug.go       
   $ CGO_CFLAGS="-Os" go build bug.go 
   

4. What did you expect to see?
   Three successful builds

5. What did you see instead?
   Two successful builds, the third build fails with

   # command-line-arguments
   ./bug.go:24:8: error: enumerator value for '__cgo_enum__0' is not an integer constant
   ./bug.go:27:8: error: enumerator value for '__cgo_enum__2' is not an integer constant
   ./bug.go:30:2: error: initializer element is not constant
   ./bug.go:30:2: error: (near initialization for '__cgodebug_data[0]')
   ./bug.go:32:2: error: initializer element is not constant
   ./bug.go:32:2: error: (near initialization for '__cgodebug_data[2]')
   

6. Additional information

   gcc version 4.9.3 (GCC)

   A successful build and a failing build with -x:

   $ go build -x bug.go                 
   WORK=/tmp/go-build161870404
   mkdir -p $WORK/command-line-arguments/_obj/
   mkdir -p $WORK/
   cd /tmp
   CGO_LDFLAGS="-g" "-O2" /usr/lib/go/pkg/tool/linux_amd64/cgo -objdir ./go-build161870404/command-line-arguments/_obj/ -importpath command-line-arguments -- -I ./go-build161870404/command-line-arguments/_obj/ bug.go
   gcc -I . -fPIC -m64 -pthread -fmessage-length=0 -I ./go-build161870404/command-line-arguments/_obj/ -g -O2 -o ./go-build161870404/command-line-arguments/_obj/_cgo_main.o -c ./go-build161870404/command-line-arguments/_obj/_cgo_main.c
   gcc -I . -fPIC -m64 -pthread -fmessage-length=0 -I ./go-build161870404/command-line-arguments/_obj/ -g -O2 -o ./go-build161870404/command-line-arguments/_obj/_cgo_export.o -c ./go-build161870404/command-line-arguments/_obj/_cgo_export.c
   gcc -I . -fPIC -m64 -pthread -fmessage-length=0 -I ./go-build161870404/command-line-arguments/_obj/ -g -O2 -o ./go-build161870404/command-line-arguments/_obj/bug.cgo2.o -c ./go-build161870404/command-line-arguments/_obj/bug.cgo2.c
   gcc -I . -fPIC -m64 -pthread -fmessage-length=0 -o ./go-build161870404/command-line-arguments/_obj/_cgo_.o ./go-build161870404/command-line-arguments/_obj/_cgo_main.o ./go-build161870404/command-line-arguments/_obj/_cgo_export.o ./go-build161870404/command-line-arguments/_obj/bug.cgo2.o -g -O2
   /usr/lib/go/pkg/tool/linux_amd64/cgo -objdir ./go-build161870404/command-line-arguments/_obj/ -dynpackage udp -dynimport ./go-build161870404/command-line-arguments/_obj/_cgo_.o -dynout ./go-build161870404/command-line-arguments/_obj/_cgo_import.go
   cd $WORK
   gcc -I . -fPIC -m64 -pthread -fmessage-length=0 -no-pie -c trivial.c
   cd /tmp
   gcc -I . -fPIC -m64 -pthread -fmessage-length=0 -o ./go-build161870404/command-line-arguments/_obj/_all.o ./go-build161870404/command-line-arguments/_obj/_cgo_export.o ./go-build161870404/command-line-arguments/_obj/bug.cgo2.o -g -O2 -Wl,-r -nostdlib -Wl,--build-id=none
   /usr/lib/go/pkg/tool/linux_amd64/compile -o ./go-build161870404/command-line-arguments.a -trimpath ./go-build161870404 -p command-line-arguments -buildid ccf8c09685ebb4ea37cf7276dea17de98672bb26 -D _/tmp -I ./go-build161870404 -pack ./go-build161870404/command-line-arguments/_obj/_cgo_gotypes.go ./go-build161870404/command-line-arguments/_obj/bug.cgo1.go ./go-build161870404/command-line-arguments/_obj/_cgo_import.go
   pack r ./go-build161870404/command-line-arguments.a ./go-build161870404/command-line-arguments/_obj/_all.o # internal
   
   
   $ CGO_CFLAGS="-Os" go build -x bug.go
   WORK=/tmp/go-build888932299
   mkdir -p $WORK/command-line-arguments/_obj/
   mkdir -p $WORK/
   cd /tmp
   CGO_LDFLAGS="-g" "-O2" /usr/lib/go/pkg/tool/linux_amd64/cgo -objdir ./go-build888932299/command-line-arguments/_obj/ -importpath command-line-arguments -- -I ./go-build888932299/command-line-arguments/_obj/ -Os bug.go
   # command-line-arguments
   ./bug.go:24:8: error: enumerator value for '__cgo_enum__0' is not an integer constant
   ./bug.go:27:8: error: enumerator value for '__cgo_enum__2' is not an integer constant
   ./bug.go:30:2: error: initializer element is not constant
   ./bug.go:30:2: error: (near initialization for '__cgodebug_data[0]')
   ./bug.go:32:2: error: initializer element is not constant
   ./bug.go:32:2: error: (near initialization for '__cgodebug_data[2]')
   

[ianlancetaylor]

The fix may be to explicitly remove any optimization options in the compilation in Package.gccErrors in cmd/cgo/gcc.go.

[rsc]

The suggestion to remove -O* options in gccErrors sounds reasonable to me. If the diff is small, this is still OK to do for Go 1.7.

[gopherbot]

CL https://golang.org/cl/23231 mentions this issue.