CakeML/cakeml

Make the heap base pointer optional

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#766 opened on Sep 17, 2020

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 (0 comments) (0 reactions) (0 assignees)Standard ML (98 forks)auto 404
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Description

The x64 generated code adds %r14 to every pointer prior to dereferencing it. This seems like a useful feature to have, since it allows a heap anywhere in the address space for large values of tagbits and lenbits and plausibly helps with a future compressed-oops/32-on-64 type feature, but for general 64-bit code you may be able to assume that the address of the heap is close to 0 and not do the add. There are potential future compatibility issues here, e.g. with ASLR and 5-level paging, so it may not make sense to do this for the shipped release artifacts.

Contributor guide

Research direction
Investigate the x64 code generation in CakeML, specifically the addition of %r14 (heap base) to every pointer. Determine scenarios where the heap base is guaranteed to be close to zero and the addition can be omitted without affecting correctness. Consider trade offs with future features like ASLR and 5 level paging.
Tech stack
None
Domain
compilersbackend
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Mostly clear
Prerequisites
Compiler code generationx64 assemblyCakeML internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20