[LLVMdev] getting started with IR needing GC

Lane Schwartz dowobeha at gmail.com
Mon Apr 28 18:19:26 PDT 2008

On Mon, Apr 28, 2008 at 2:13 PM, Gordon Henriksen
<gordonhenriksen at mac.com> wrote:
>  > If so, then a Collector plugin would need to have info about every
>  > supported backend lays out the runtime stack?
>  Yes. This information is actually available in a target-independent
>  fashion with LLVM, so the Collector interface is target-independent. A
>  backend that doesn't use the target-independent back-end could also
>  implement support for values of gc "...", but this is quite
>  hypothetical.

Right. So a GC plugin needs to know a few things in order to find GC
roots. It needs to know the stack pointer, the frame pointer, possibly
static links (if we allow nested functions), and where in the stack
frame local variables live.

How do you get access to this data in a platform-agnostic manner?

>  Such a runtime will further need a way to crawl the native call stack
>  and discover the return address of each call frame. LLVM doesn't
>  provide such a facility.

I guess I'm missing something here. Why does the GC need the return addresses?


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