xenia-project/xenia

DIV_I32 and others don't handle INT_MIN / -1

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#1085 opened on Feb 12, 2018

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 (2 comments) (5 reactions) (0 assignees)C++ (7,418 stars) (1,077 forks)batch import
cpugood first issue

Description

https://github.com/benvanik/xenia/blob/190108dab6732d9db5c8595e1358b7b034cb5a14/src/xenia/cpu/backend/x64/x64_sequences.cc#L4332

It was pointed out to me that x86 will raise an exception when dividing INT_MIN by -1. I haven't encountered any games doing this yet - but it could potentially be an issue.

According to PowerPC docs, the output is undefined if this condition occurs.

Could be worth investigating if you're a new contributor.

Contributor guide

Tech stack
cpp
Domain
backend
Issue type
bug
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.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
C++ programmingx86 assembly basicsinteger overflow concepts
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
Examine the function at src/xenia/cpu/backend/x64/x64 sequences.cc around line 4332. Understand the DIV I32 instruction handling and test for INT MIN / 1. Add a conditional check to handle this case as per PowerPC undefined behavior. Also consider whether the emulator should ignore the exception or replicate the x86 behavior.