Site Home Page The UML Wiki UML Community Site The UML roadmap What it's good for Case Studies Kernel Capabilities Downloading it Running it Compiling Installation Skas Mode Incremental Patches Test Suite Host memory use Building filesystems Troubles User Contributions Related Links The ToDo list Projects Diary Thanks Contacts
Tutorials The HOWTO (html) The HOWTO (text) Host file access Device inputs Sharing filesystems Creating filesystems Resizing filesystems Virtual Networking Management Console Kernel Debugging UML Honeypots gprof and gcov Running X Diagnosing problems Configuration Installing Slackware Porting UML IO memory emulation UML on 2G/2G hosts Adding a UML system call Running nested UMLs
How you can help Overview Documentation Utilities Kernel bugs Kernel projects
Screenshots A virtual network An X session
Transcripts A login session A debugging session Slackware installation
Reference Kernel switches Slackware README
Papers ALS 2000 paper (html) ALS 2000 paper (TeX) ALS 2000 slides LCA 2001 slides OLS 2001 paper (html) OLS 2001 paper (TeX) ALS 2001 paper (html) ALS 2001 paper (TeX) UML security (html) LCA 2002 (html) WVU 2002 (html) Security Roundtable (html) OLS 2002 slides LWE 2005 slides
Fun and Games Kernel Hangman Disaster of the Month

### UML on 2G/2G hosts

Introduction

> Most Linux machines are configured so that the kernel occupies the upper 1G (0xc0000000 - 0xffffffff) of the 4G address space and processes use the lower 3G (0x00000000 - 0xbfffffff). However, some machine are configured with a 2G/2G split, with the kernel occupying the upper 2G (0x80000000 - 0xffffffff) and processes using the lower 2G (0x00000000 - 0x7fffffff).

The problem

> The prebuilt UML binaries on this site will not run on 2G/2G hosts because UML occupies the upper .5G of the 3G process address space (0xa0000000 - 0xbfffffff). Obviously, on 2G/2G hosts, this is right in the middle of the kernel address space, so UML won't even load - it will immediately segfault.

The solution

> The fix for this is to rebuild UML from source after enabling CONFIG_HOST_2G_2G (under 'General Setup'). This will cause UML to load itself in the top .5G of that smaller process address space, where it will run fine. See this page if you need help building UML from source.

Hosted at