Golang binary dwarf

[Florian Weimer]

* Mark Wielaard:

> Hi Manoj,
>
> On Sat, 2021-02-06 at 07:03 +0000, Manoj Kumar via Elfutils-devel
> wrote:
>> Hi,Using dyninst, I am trying to access local variables and arguments
>> of a function which is part of a go binary.To get local variables,
>> dyninst uses libdw to find all the modules. It uses dwarf_nextcu
>> function of libdw to find all the modules of binary.When I compile a
>> go binary using "go build filename.go" then dwarf_nextcu finds all
>> the modules (almost 118) and dyninst is able to access local
>> variables and arguments of any function.But when I compile a go
>> binary with linkshared option  "go build -linkshared filename.go"
>> then dwarf_nextcu finds only 5 modules. Due to that, dyninst is not
>> able to access any variable of a function.
>> Does go binary with linkshared option has different version of dwarf?
>> Could you please suggest how to use libdw for go binary with
>> linkshared option.
>
> Could you explain what the linkshared option is and what it does?

$ go tool link -help
[…]
  -linkshared
    	link against installed Go shared libraries
[…]

The Fedora version is broken, unfortunately:

$ cat t.go
package main
func main() { }
$ go build -linkshared t.go 
go build runtime/internal/sys: copying /home/fweimer/.cache/go-build/ef/ef8092ebd194e7ec34c864584fc2216541454e9626c98ffe9d5210d2784da429-d: open /usr/lib/golang/pkg/linux_amd64_dynlink/runtime/internal/sys.a: permission denied
go build internal/cpu: copying /home/fweimer/.cache/go-build/ca/ca0a2dbbc130aa21613ca27f378b8c9fda02c4082687d92b40a0d6c660bc86d1-d: open /usr/lib/golang/pkg/linux_amd64_dynlink/internal/cpu.a: permission denied
[…]
$ rpm -qf /usr/bin/go
golang-bin-1.15.7-1.fc33.x86_64

Filed here: <https://bugzilla.redhat.com/show_bug.cgi?id=1688261>

So I'm not sure how we can reproduce the elfutils issue. 8-/

Thanks,
Florian
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