Go: question: how to put breakpoint to a Go method with gdb or delve

[vigneshkm]

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

$ go version
go version go1.9.2 linux/amd64

Does this issue reproduce with the latest release?

Didnt check as this is a query related to debuggers with go rather than go itself

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

go env Output

$ go env

GOARCH="amd64"

GOBIN=""

GOEXE=""

GOHOSTARCH="amd64"

GOHOSTOS="linux"

GOOS="linux"

GOPATH="/home/vignesh/go-book/"

GORACE=""

GOROOT="/usr/local/go"

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

GCCGO="gccgo"

CC="gcc"

GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build931353307=/tmp/go-build -gno-record-gcc-switches"

CXX="g++"

CGO_ENABLED="1"

CGO_CFLAGS="-g -O2"

CGO_CPPFLAGS=""

CGO_CXXFLAGS="-g -O2"

CGO_FFLAGS="-g -O2"

CGO_LDFLAGS="-g -O2"

PKG_CONFIG="pkg-config"

What did you do?

I want to debug a go code. I want to put breakpoint on a method (belonging to a named type) in a imported package. I went through a lot of online materials where they only put breakpoints on a line number in file (eg:breakpoint a.go:15).

I have done a lot of debugging in 'C' where I put breakpoints on functions. Is this kind of debugging possible in go??

I have the following code in my main package.

clientContext := sdk.Context(fabsdk.WithUser("Admin"), fabsdk.WithOrg("ordererorg")).

I want to put breakpoints to

1) function WithUser() which belongs to package fabsdk in file github.com/hyperledger/fabric-sdk-go/pkg/fabsdk/context.go.
2) method Context() belonging to type FabricSDK in file github.com/hyperledger/fabric-sdk-go/pkg/fabsdk/fabsdk.go in package fabsdk.

Is it possible to put breakpoints to method WithUser() and context() or Is breakpoints only allowed at a line number in a file?? I could use either gdb or delve or any other debugger as well.

What did you expect to see?

need to put breakpoints on a method or function

What did you see instead?

(gdb) br sdk.Context
Function "sdk.Context" not defined.
Make breakpoint pending on future shared library load? (y or [n]) n

(gdb) br github.com/hyperledger/fabric-sdk-go/pkg/fabsdk.Context
Function "github.com/hyperledger/fabric-sdk-go/pkg/fabsdk.Context" not defined.
Make breakpoint pending on future shared library load? (y or [n]) y
Breakpoint 2 (github.com/hyperledger/fabric-sdk-go/pkg/fabsdk.Context) pending.

[cherrymui]

(for gdb)

function WithUser() which belongs to package fabsdk in file github.com/hyperledger/fabric-sdk-go/pkg/fabsdk/context.go.

Try b github.com/hyperledger/fabric-sdk-go/pkg/fabsdk.WithUser?

method Context() belonging to type FabricSDK in file github.com/hyperledger/fabric-sdk-go/pkg/fabsdk/fabsdk.go in package fabsdk.

Try b 'github.com/hyperledger/fabric-sdk-go/pkg/fabsdk.(*FabricSDK).Context'?

In general, the symbol name of a method is pkg_path.T.M for value method or pkg_path.(*T).M for pointer method.

[vigneshkm]

@cherrymui , I tried your solution with delve and it works. Thank you very much for your response and the explanation of path of a symbol :)

[josharian]

I'd actually like to re-open this as a feature request. Writing out the full symbol name is onerous. I often resort to running nm/objdump, grepping for the function name I want, and then using the address instead.

It'd be nice if delve did some/all of these things:

• Given b WithUser and only a single function containing the substring WithUser, set a breakpoint on it and print what it resolved to.
• Given b WithUser, print a list of all symbols containing the substring WithUser, so that the user can easily copy/paste one.
• Add a command like resolve WithUser that prints a list of all symbols with the substring WithUser.

cc @aarzilli @heschik @thanm

[josharian]

Bonus: support the same features in gdb/lldb!

Also cc @dr2chase @aclements (I'm not sure exactly who the debugger team is nowadays)

[aarzilli]

Just b Context is probably ambiguous but delve should be able to resolve something like b FabricSDK.Context or b fabsdk.Context correctly. Supporting something like this in lldb would require writing a language layer for it (which existed for a while until it was removed because nobody maintained it).

[josharian]

Even if b Context is ambiguous, delve could print all the possible disambiguations (up to some limit), no? That’d be more useful than simply rejecting it.

I didn’t realize the lldb script had been removed. Bummer.

[aarzilli]

Even if b Context is ambiguous, delve could print all the possible disambiguations (up to some limit), no?

yes, and it does.

[aclements]

You can also place a breakpoint using a line number, like "br fabsdk/context.go:NNN". I believe in gdb it will do some amount of disambiguation of the file name, so you don't have to type the full path to use this syntax.

[heschik]

And just for the record, I don't think there's anything in the compiler/linker we can do to affect any of this. Maybe we could do something in runtime-gdb.py? But to me this seems like a Delve feature request, if anything.

[cherrymui]

I agree with @heschik that this is more on the debugger side than the compiler side.

Ideally maybe gdb/lldb should probably just hint symbols with partial matches. C++ function names are also quite long, in many cases.

[andybons]

@josharian would you mind updating the title of this issue with what you'd like to accomplish? Should your feature requests be separate issues perhaps?

[josharian]

Re-reading this thread, I think I'll just close it.