go build doesn't propagate options that disable optimizations

[ptu...@gmail.com]

I build my Go project with the -N and -l options, but they only seem to apply to the top-most package -- imported packages are still optimized.  From what I can tell, this is because go build isn't propagating the options that disable optimization as it tracks down and builds dependencies.

I claim that:

• If I tell  go build  to disable optimizations, it makes sense that optimizations should be disabled for everything it ends up building.
  
  
• Therefore, this is a bug.

I'm writing here because I'm a Go n00b, and there may be something I'm missing.

Let me show my evidence...

Consider the following trivial Go project:

.

├── main.go

└── help

    └── help.go

Here's main.go:

package main

import "./help"

func main() {

    help.Help()

}

Here's help.go:

package help

import "fmt"

func Help() {

    fmt.Println("I'm helping")

}

Here's how I built the project:

go build -gcflags="-N -l" main.go

The -N option disables optimization, and the -l option disables inlining.

This produced an executable called main in my current directory (as expected).  I tried to debug this executable with delve and saw this:

$ dlv exec main

Type 'help' for list of commands.

(dlv) b main.main

Breakpoint 1 set at 0x108e83f for main.main() ./main.go:5

(dlv) c

> main.main() ./main.go:5 (hits goroutine(1):1 total:1) (PC: 0x108e83f)

     1: package main

     2:

     3: import "./help"

     4:

=>   5: func main() {

     6:     help.Help()

     7: }

(dlv) s

> main.main() ./main.go:6 (PC: 0x108e84b)

     1: package main

     2:

     3: import "./help"

     4:

     5: func main() {

=>   6:     help.Help()

     7: }

(dlv) s

> _/Users/pturley/Workspace/Go/src/debug-problem/help.Help() ./help/help.go:5 (PC: 0x108e76f)

Warning: debugging optimized function

     1: package help

     2:

     3: import "fmt"

     4:

=>   5: func Help() {

     6:     fmt.Println("I'm helping")

     7: }

Notice that main() isn't optimized (as expected), but Help() is optimized, and delve prints a warning about that.  If, for example, Help() had local variables, it would be unlikely you could view their values.

I tried building again with a few more options:

go build -a -x -gcflags="-N -l" main.go > log 2>&1

The -a option ensures Go doesn't rely on any cached build artifacts.  The -x option causes Go to print all commands before executing them.

Here's the command that built main.go (white space inserted to improve clarity):

/opt/local/lib/go/pkg/tool/darwin_amd64/compile

    -o $WORK/b001/_pkg_.a

    -trimpath $WORK/b001

    -N -l

    -p main

    -complete

    -buildid XMSzm8g7wNG80cfFP4Nw/XMSzm8g7wNG80cfFP4Nw

    -goversion go1.10

    -D _/Users/pturley/Workspace/Go/src/debug-problem

    -importcfg $WORK/b001/importcfg

    -pack -c=4

    ./main.go

Here's the command that built help.go:

/opt/local/lib/go/pkg/tool/darwin_amd64/compile

    -o $WORK/b002/_pkg_.a

    -trimpath $WORK/b002

    -p _/Users/pturley/Workspace/Go/src/debug-problem/help

    -complete

    -buildid Td3vdeSGgO-nwcrs810U/Td3vdeSGgO-nwcrs810U

    -goversion go1.10

    -D _/Users/pturley/Workspace/Go/src/debug-problem/help

    -importcfg $WORK/b002/importcfg

    -pack -c=4

    ./help.go

Note that the -N and -l options are missing in the latter command.  If they had been propagated by  go build (which I claim makes the most sense), all my code would be debuggable.

[matthe...@gmail.com]

This looks like it changed between 1.9.4 and 1.10.

Here’s the documentation: https://github.com/golang/go/blob/release-branch.go1.10/src/cmd/go/internal/work/build.go#L113-L127

I guess the package patterns thing is new. Try this:

go build -a -x -gcflags=“all=-N -l”

Matt

[Patrick Turley]

Indeed -- that pattern made the difference.

Thank you.

[Florin Pățan]

My understanding is that you do not need -a anymore, just the rest of the flags.

[jake...@gmail.com]

For completeness, this is documented in the 1.10 release notes. See the second paragraph of this section: https://golang.org/doc/go1.10#build.