Dylan Foundry

Deepening LLDB Integration

A previous post covered the subject of the initial LLDB and Dylan integration.

While much of this post discusses what we did to improve Dylan integration, the overall techniques are broadly useful for many languages. In fact, if anyone is interested, I am available for consulting on this topic. Just email me.

Catching Up

In the previous post, we talked about changing the base representation from void* to uintptr_t to work around a bug in LLDB. This was, in part, due to our goal to try to have the integration work with the currently shipping version of LLDB.

Unfortunately, this work won't be completed and merged. In separate developments, it has emerged that it can be unsafe to treat a pointer as an integer when working with a garbage collector. The details of this are quite interesting, so out of an abundance of caution, we will not be going down this route.

Expanding Objects

We are able to use the "pointer depth" parameter to commands like expression and frame variable to show the "expanded" form of objects:

(lldb) frame variable -P 1 T15
(dylan_value) T15 = 0x017e8000 {<buffer>} {
  [buffer-next] = 0x00000001 {<integer>: 0}
  [buffer-end] = 0x00000001 {<integer>: 0}
  [buffer-position] = 0x00000001 {<integer>: 0 ...
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There are comments.

Integrating with LLDB

I spend a lot of time debugging Dylan code. Up until now, this has been a somewhat painful process when not using the IDE on Windows. (And I don't really use the IDE on Windows as it doesn't fit well into my workflow.) I finally reached the point where I decided that I wanted to improve our debugger integration.

Much of what is described below may be applicable to people working on debugging support for other languages.

Current State of Dylan Debugging

We have a debugger on Windows integrated with our IDE. This facility is not available on the other platforms that we support. There are many reasons for this:

  • The debug info that Open Dylan generates is only done on Windows.
  • The debugger code for interacting with the OS is only implemented for Windows.
  • The IDE itself is only available on Windows.

This means that debugging on Linux, FreeBSD and Mac OS X has traditionally been more challenging. We often resort to "printf debugging" and have some basic debug printing functions that can be invoked from the compiler so long as they don't crash. Debugging is really only effective with the C back-end as the HARP ...

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There are comments.

The Dylan Foundry is working on tools and libraries to make it easier to use the Dylan programming language in production.