Incorrect position of "--args" gdb argument prevents correct processing of target program arguments.

[HattonLe]

VS Code Version: 1.124.2
OS Version: Ubuntu 26.04 kernel 7.0.0 (compiled from source).

Steps to Reproduce:

1 Find a example C program that demonstrates the use of argp (there are lots around).
2 Using gdb from a command line, debug that app using the "--args" flag plus various args for the app.
for example /usr/bin/gdb --args ./testapp --device=/dev/xyz --syslog --ver=9 --show --quiet --config=/etc/xyz.conf
3 Now try debugging that using Visual Code, without using the launch setting "miDebuggerArgs".
You will find the test app won't process its args corrrectly.
4 Now try debugging again but using the launch setting "miDebuggerArgs": "--args".
You will find the test app still won't process its args correctly.

The problem (this took me an entire day to figure out because the problem wasn't in my test app at all!).
(The following example outputs are from my test app using the different ways of launching gdb described above) .

Debugging my test app using gdb from the command line works perfectly because the "--args" option appears just before the target executable, and so gdb passes all the following arguments to the target main().
ARGP_KEY_INIT
parse_opt() key:64 char:d arg:/dev/xyz
parse_opt() key:6C char:l arg:(null)
parse_opt() key:76 char:v arg:9
parse_opt() key:73 char:s arg:(null)
parse_opt() key:71 char:q arg:(null)
parse_opt() key:63 char:c arg:/etc/xyz.conf
ARGP_KEY_NO_ARGS
ARGP_KEY_END
ARGP_KEY_SUCCESS
ARGP_KEY_FINI
argp_parse() done
The above is the expected output with all app arguments correctly processed.

However using Visual Code debugging without the "miDebuggerArgs": "--args" launch property -
ARGP_KEY_INIT
parse_opt() key:64 char:d arg:/dev/xyz --syslog --verbose=9 --showkey --quiet --config=/etc/xyz.conf
ARGP_KEY_NO_ARGS
ARGP_KEY_END
ARGP_KEY_SUCCESS
ARGP_KEY_FINI
argp_parse() done
This is incorrect. The app only processed a single argument that was the entire argument string given to the app.

And using Visual Code debugging with the "miDebuggerArgs": "--args" launch property -
ARGP_KEY_INIT
parse_opt() key:64 char:d arg:/dev/xyz --syslog --verbose=9 --showkey --quiet --config=/etc/xyz.conf
ARGP_KEY_NO_ARGS
ARGP_KEY_END
ARGP_KEY_SUCCESS
ARGP_KEY_FINI
argp_parse() done
This is still incorrect, adding the "--arg" option via the "miDebuggerArgs" launch property didn't do anything as it was not placed in the correct position when invoking gdb.
I get this in my Visual Code terminal window after a run using the "--arg" property -
[1] + Done "/usr/bin/gdb" --interpreter=mi --args --tty=${DbgTerm} 0<"/tmp/Microsoft-MIEngine-In-u5ai3hek.04x" 1>"/tmp/Microsoft-MIEngine-Out-lot3j3jx.fqc"

Perhaps Visual Code should have placed "--args" after the "--tty" ????

[gregg-miskelly]

Can you share your launch.json configuration?
Why are you using miDebuggerArgs instead of args?

[HattonLe]

because I imagine "miDebuggerArgs" is supposed to be for arguments to the debugger, and "Args" is for arguments to the target application.
When you use gdb standalone, "--args" is special in that it has to go in front of the target executable on the command line.
whereas all target arguments go after the target executable name.
The reason for that is "--args" tells gdb that everything following should be passed to the target executable, and that it should not be processing them itself.

[gregg-miskelly]

because I imagine "miDebuggerArgs" is supposed to be for arguments to the debugger, and "Args" is for arguments to the target application.

Agreed. That is why I am confused why you would stick --args in miDebuggerArgs instead of using the launch.json args property.

[HattonLe]

from my original issue comment - the command line used -->
/usr/bin/gdb --args ./testapp --device=/dev/xyz --syslog --ver=9 --show --quiet --config=/etc/xyz.conf
^^^^ everything after this point on the command line is handled by ./testapp.
if you don't use "--args", gdb would try and evaluate the options for itself.

I am just a user of Visual Code. I didn't write it and I don't know how it works internally. All I know is that it took me a whole day to figure out it wasn't me causing the problem.

[gregg-miskelly]

I am assuming your goal is to debug .\testapp with arguments --device=/dev/xyz --syslog --ver=9 --show --quiet --config=/etc/xyz.conf. Is that correct?

If so, here is what your launch.json should look like. Can you try this and tell me if it doesn't work?

            "program": "${workspaceFolder}/testapp",
            "args": [ "-device=/dev/xyz", "--syslog", "--ver=9", "--show", "--quiet", "--config=/etc/xyz.conf" ],
            "cwd": "${workspaceFolder}"

[HattonLe]

Yes that doesn't work.
My exact launch configuration is as follows (to allow me to switch between gdb as user or as root I swap between the "miDebuggerPath" lines below. (this issue occurs with either user, so either way the target app (which uses Argp) ends up seeing just 1 single argument string containing everything after "./testapp", instead of 5 individual arguments).

{
  "version": "0.2.0",
  "configurations": [
    {
      "name": "(gdb) Launch testapp",
      "type": "cppdbg",
      "request": "launch",
      "program": "${workspaceFolder}/testapp",
      "args": [
        "--syslog --device=/dev/testapp --verbose=9 --showkey --showexec --quiet --config=/etc/xyz.conf"
      ],
      "stopAtEntry": false,
      "cwd": "${workspaceRoot}",
      "externalConsole": false,
      "MIMode": "gdb",

//      "miDebuggerPath": "/usr/bin/gdb",
      "miDebuggerArgs": "--args",
      "miDebuggerPath": "${workspaceFolder}/gdb_root.sh",
      "setupCommands": [
        {
          "description": "Enable pretty-printing for gdb",
          "text": "-enable-pretty-printing",
          "ignoreFailures": true
        },
        {
          "description": "Set Disassembly Flavor to Intel",
          "text": "-gdb-set disassembly-flavor intel",
          "ignoreFailures": true
        }
      ]
    }
  ]
}

And the usual contents for "gdb_root.sh" -->

SELF_PATH=$(realpath -s "$0")

if [[ "$SUDO_ASKPASS" = "$SELF_PATH" ]]; then
    zenity --password --title="$1"
else
    exec env SUDO_ASKPASS="$SELF_PATH" sudo -A /usr/bin/gdb $@
fi