cmds/command: Include hidden flag -c for coredumpctl support

[Foxboron]

coredumpctl attempts to pass the core file to the debugger through the -c flag. However delve does not support such a flag.

This patch makes it a bool flag so we can receive the coredump file from coredumpctl

$ GOTRACEBACK=crash ./main
panic:
goroutine 1 [running]:
[....]
zsh: IOT instruction (core dumped)  GOTRACEBACK=crash ./main
$ coredumpctl list main
TIME                            PID  UID  GID SIG     COREFILE EXE                             SIZE
Tue 2022-11-15 23:29:07 CET 2047401 1000 1000 SIGABRT present  /tmp/go-test/main 60.2K
$ coredumpctl gdb --debugger=dlv -A core main
           PID: 2047401 (main)
        Signal: 6 (ABRT)
     Timestamp: Tue 2022-11-15 23:29:07 CET (1min 27s ago)
  Command Line: ./main
    Executable: /tmp/go-test/main
     Owner UID: 1000 (fox)
  Size on Disk: 60.2K
       Message: Process 2047401 (main) of user 1000 dumped core.

                Module /tmp/go-test/main without build-id.
                Stack trace of thread 2047401:
                #0  0x000000000045fa01 n/a (/tmp/go-test/main + 0x5fa01)
                #1  0x0000000000446d3e n/a (/tmp/go-test/main + 0x46d3e)
                #2  0x0000000000445487 n/a (/tmp/go-test/main + 0x45487)
                #3  0x000000000045fce6 n/a (/tmp/go-test/main + 0x5fce6)
                #4  0x000000000045fde0 n/a (/tmp/go-test/main + 0x5fde0)
                #5  0x0000000000432a49 n/a (/tmp/go-test/main + 0x32a49)
                #6  0x000000000043211a n/a (/tmp/go-test/main + 0x3211a)
                #7  0x000000000048d405 n/a (/tmp/go-test/main + 0x8d405)
                #8  0x0000000000434db2 n/a (/tmp/go-test/main + 0x34db2)
                #9  0x000000000045e0e1 n/a (/tmp/go-test/main + 0x5e0e1)
                ELF object binary architecture: AMD x86-64

[dlv core /tmp/go-test/main -c /var/tmp/coredump-JizL2g]
Type 'help' for list of commands.
(dlv) list main.main
Showing /tmp/go-test/main.go:3 (PC: 0x457c26)
     1:	package main
     2:
     3:	func main() {
     4:		panic()
     5:	}
(dlv)

Signed-off-by: Morten Linderud morten@linderud.pw

[Foxboron]

The reason why this is neat is because we could run Go binaries from distributions in services with GOTRACEBACK=crash and leverage debuginfod to fetch symbols from crashing systems. It would probably be a good idea to document this as well, but testing the waters with an implicit flag first :)

[aarzilli]

TestGeneratedDoc in dlv_test.go fails because the documentation hasn't been regenerated. To actually make the flag hidden you have to call coreCommand.Flags().MarkHidden("core"), I think.

[derekparker]

It should also be noted that Delve supports debuginfod already: https://github.com/go-delve/delve/blob/master/pkg/proc/debuginfod/debuginfod.go.

[Foxboron]

@derekparker Yes, I implemented some of that and see coredumpctl as a natural extension to this :)

This feature set should maybe be documented a bit better because it's quite neat.

A quick recording of be crashing the Arch packaged delve and using this patch to debug the stack trace with stuff fetched from debuginfod.

https://paste.xinu.at/wp7pZBzekQQERwvN2/

[aarzilli]

LGTM

[aarzilli]

This feature set should maybe be documented a bit better because it's quite neat.

I'm not sure where the right place for this would be. Could be inside Gettting started but it would probably have to be in the context of a broader discussion on generating and debugging core files.