Porting LLVM to a new OS Kai Nacke 31 January 2016 LLVM devroom @ - - PowerPoint PPT Presentation

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Porting LLVM to a new OS Kai Nacke 31 January 2016 LLVM devroom @ FOSDEM16 Porting LLVM There are two possible goals Run LLVM tools on OS Generate code for OS / CPU architecture Mission is to run LLVM on previously unsupported

SLIDE 1

Porting LLVM to a new OS

Kai Nacke 31 January 2016 LLVM devroom @ FOSDEM‘16

SLIDE 2

Porting LLVM

There are two possible goals

– Run LLVM tools on OS – Generate code for OS / CPU architecture

Mission is to run LLVM on previously

unsupported OS and adding code generation for the OS

Adding a new CPU architecture is a major task

– Not considered here

31 January 2016 Kai Nacke | Porting LLVM to a new OS 2

SLIDE 3

A very brief look on AIX

OS for mission critial tasks
A UNIX OS, supports System V and BSD APIs
Runs on POWER architecture

– Already a target for LLVM

Good software support

– Native toolchain – Major Open Source Software available

31 January 2016 Kai Nacke | Porting LLVM to a new OS 3

SLIDE 4

Toolchain

Prerequisites for LLVM are available

– gcc, cmake, gmake, … – Use this toolchain

GNU tools use as and ld from OS

– Expect different command line options

Not every package works out of the box

– Python 2.7.x is missing => compile yourself – cmake 3.x had problems => use cmake 2.8.x

31 January 2016 Kai Nacke | Porting LLVM to a new OS 4

SLIDE 5

Compile LLVM

First compiler run identifies code problems

– Missing endian definitions – Wrong path handling code choosen

Linking fails because of unsupported options

– Updates to the cmake modules necessary

Still problems with ThreadPool code

– Needs more investigation

31 January 2016 Kai Nacke | Porting LLVM to a new OS 5

SLIDE 6

Running LLVM on AIX

All LLVM tools are compiled and run
Results of test suite are similar to Linux/PPC
Still no code generation for AIX

31 January 2016 Kai Nacke | Porting LLVM to a new OS 6

SLIDE 7

Code Generation

LLVM misses code generation for AIX
You can‘t use the Linux/PPC ELF-based tools

– Binary format is XCOFF – Textual assembler is different

Idea is to tweak assembler generation and use

external assembler to create object file

31 January 2016 Kai Nacke | Porting LLVM to a new OS 7

SLIDE 8

XCOFF

XCOFF is an extended COFF format
Basically it adds the TOC concept to COFF
Major differences to COFF

– No PE header – Smallest adressable unit is csect – A csect always has a storage class associated

Assembler text uses .csect

31 January 2016 Kai Nacke | Porting LLVM to a new OS 8

SLIDE 9

Partial Class Hierarchy

PPCAIXAsmPrinter PPCAsmPrinter AsmPrinter Triple MCAsmInfoXCOFF MCAsmInfoCOFF MCAsmInfo

<<uses>>

MCSectionCOFF MCSection

<<uses>> <<uses>>

…

new new

PPCAsmInfoXCOFF

new

MCObjectFileInfo

<<uses>> <<instantiates>>

changed changed changed

UsesAIXSectionDirective usesAIXSectionDirective() 31 January 2016 Kai Nacke | Porting LLVM to a new OS 9

changed

SLIDE 10

Implementation

Outputs .section as .csect

– Required lot of changes

Makes storage class part of section name

– Only a hack

Use raw text output for missing op‘s
Relocation syntax requires more work

31 January 2016 Kai Nacke | Porting LLVM to a new OS 10

SLIDE 11

Summary / Outlook

First patches submitted
Work on relocation syntax required

– Needed for „Hello World“ application

Working approach
Next step is dumping of XCOFF files

31 January 2016 Kai Nacke | Porting LLVM to a new OS 11