add a gdb wrapper capable of lazy loading pwndbg's gdbinit.py

[fidgetingbits]

Description of changes

Adds a gdb wrapper whose environment is capable of lazy loading pwndbg via gdbinit.py. The use case is that I very often have to run gdb without pwndbg in order to setup initial debugging and attach to remote targets, to avoid crashes/errors, but once I hit the state that I actually want to proper analysis I load pwndbg. Some of the things that caused this to be required can be (and have been) fixed upstream in pwndbg, but the reality is day-to-day I still need use this approach and have been for years.

So the idea is from your dev shell (or wherever) you would use gdb-with-pwndbg-env (via aliasing gdb cmd or manually running), then when you actually need pwndbg you source ~/.nix-profile/share/pwndbg/gdbinit.py. The way I've been dealing with this in my devshells is using something like this:

sed -e 's/^exec \(.*\)-x.*/export PWNDBG_VENV_PATH=PWNDBG_PLEASE_SKIP_VENV\nexec \1 "\$@"/g' ${pkgs.lib.getBin pkgs.pwndbg}/bin/pwndbg > debug/gdb-with-pwndbg-env

But, I'd rather have a solution in nixpkgs itself if possible, as it will benefit other pwndbg users.

I'm open to a different name for gdb-with-pwndbg-env; I'm not sure if there's precedent for this type of thing elsewhere in nixpkgs, so maybe there is a standard.

@Mic92 @patryk4815 @msanft

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 24.05 Release Notes (or backporting 23.05 and 23.11 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[Mic92]

Quiet a long name but I can also not think of a better one.

[Mic92]

I think the standard is usually to have a gdb.withPlugins wrapper. But potentially the gdb ecosystem is not big enough for that.

[patryk4815]

maybe better option would be something like pwndbg --lazy-init

[Mic92]

What do you think about this solution? #307655
It should still allow you to load ~/.nix-profile/share/pwndbg/gdbinit.py but now you can just use the normal gdb executable.

[fidgetingbits]

That's much better imo, tested and works fine afaict. Happy to go that route unless other maintainers see any issue. I'll close this PR.