gdbinit file and helpers

[QDucasse]

Hello,
This pull request adds a .gdbinit file that can be copied at ~/.gdbinit to get common debugging functions and shortcuts for the Pharo VM. The list of all user-defined functions can be accessed in gdb with help user-defined and documentation for a specific function with help function_name.

Printing:

Command	Arguments	Description
ptt	-	Print trampoline table
pf	frame address	Print frame info
pcog	cog method address	Print cog method info
pcogs	-	Print all cogged methods
pct	cog method type	Print all cog methods of a given type
pcp	primitive index	Print all cog methods using a given primitive
pcm	compiled method address	Print all cog methods of a given method
pcs	selector address	Print all cog methods for a given selector

Locating and Disassembling

Command	Arguments	Description
whereis	address	Locates the enclosing cog method or trampoline
dt	trampoline address	Disassemble the given trampoline
dc	cog method address (optional length)	Disassemble the cog method (splits metadata/checks/method body) up to a given length if provided (all method otherwise)
dnc	cog method address (optional length)	Disassemble the cog method (starting at the method body) up to a given length if provided (all method otherwise)

[guillep]

This is super nice! Thanks Q.

I'll integrate it and put your comment into a wiki page.
BTW, do you have an already written little tutorial on how to debug the JIT? I'm interested on that too :)

[guillep]

FYI https://github.com/pharo-project/pharo-vm/wiki/Debugging-with-GDB

GitHub

Debugging with GDB · pharo-project/pharo-vm Wiki

This is the VM used by Pharo. Contribute to pharo-project/pharo-vm development by creating an account on GitHub.

[QDucasse]

Happy to help! The small tutorial is here: https://qducasse.github.io/posts/jit_debug/
(or the sources at https://github.com/QDucasse/bloggy/blob/main/content/posts/jit_debug.md)! Maybe it can go along with the page above!

Debugging Pharo JIT code in gdb

Investigating VM runtime crashes can be obscure, especially when dealing with code that has been recompiled to machine code by the JIT compiler. This post will show the way to track the execution path within gdb. Note that you will need gdb to be available to debug the VM, it is not possible to do this through a simple qemu image (at least by default) or user-space simulation such as qemu-debootstrap.

GitHub

bloggy/jit_debug.md at main · QDucasse/bloggy

Sources for my blog https://qducasse.github.io. Contribute to QDucasse/bloggy development by creating an account on GitHub.

[guillep]

@QDucasse would you mind if we move some of your writeups to the wiki under your name?

[guillep]

I thought this was safe, but this is making the build fail (not compile) due the the missing printStringOf.

I'll revert it and reopen it

[guillep]

Reverted in #485. I'll see how we can reopen this PR