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c© 2010 IBM Corporation
IBM Linux Technology Center
Porting Linux to a new architecture, done right
Arnd Bergmann
Porting Linux to a new architecture, done right
Overview
1 Status of new architecture ports2 Typical approaches to new architectures3 Lessons Learned
2 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
About me
s390 architecture 2002-2005PowerPC/Cell architecture 2005-now32/64 bit syscall emulationMaintaining include/asm-genericReviewing new architecturesLearning about ARM
3 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Recently merged architectures
2.6.13 2.6.19 2.6.22 2.6.28 2.6.30 2.6.32 2.6.36
100000
1000000
10000000
100000000
tile
s*core
microblaze
mn10300
blackfin
avr32
xtensa
arm
4 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Upcoming architectures
nios IIlm32UniCoreOpenRISCc64xMMIXnameless 48-bit architecturenameless DSP architecture
5 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
What makes architecture ports so hard?
Typical approaches to new architectures
6 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Language barrier #1: English
Homes of the current architecture maintainers
7 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Language barrier #2: C
pragmatically object-oriented freestandingILP32/LP64 GNU
C
99 with static annotationsand enforced coding style
8 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Language barrier #2: C
pragmatically object-oriented freestandingILP32/LP64
GNU C99
with static annotationsand enforced coding style
8 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Language barrier #2: C
pragmatically object-oriented freestandingILP32/LP64
GNU C99 with static annotations
and enforced coding style
8 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Language barrier #2: C
pragmatically object-oriented freestanding
ILP32/LP64 GNU C99 with static annotations
and enforced coding style
8 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Language barrier #2: C
pragmatically object-oriented
freestandingILP32/LP64 GNU C99 with static annotations
and enforced coding style
8 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Language barrier #2: C
pragmatically
object-oriented freestandingILP32/LP64 GNU C99 with static annotations
and enforced coding style
8 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Language barrier #2: C
pragmatically object-oriented freestandingILP32/LP64 GNU C99 with static annotations
and enforced coding style
8 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Language barrier #2: C
pragmatically object-oriented freestandingILP32/LP64 GNU C99 with static annotationsand enforced coding style
8 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Architectural challenges
Symmetric Multiprocessing
Noncoherent I/OOut-of-order I/OMemory management unitsMultiple ABIsMultiple ISAsMultiple platformsTimekeeping
9 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Architectural challenges
Symmetric MultiprocessingNoncoherent I/O
Out-of-order I/OMemory management unitsMultiple ABIsMultiple ISAsMultiple platformsTimekeeping
9 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Architectural challenges
Symmetric MultiprocessingNoncoherent I/OOut-of-order I/O
Memory management unitsMultiple ABIsMultiple ISAsMultiple platformsTimekeeping
9 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Architectural challenges
Symmetric MultiprocessingNoncoherent I/OOut-of-order I/OMemory management units
Multiple ABIsMultiple ISAsMultiple platformsTimekeeping
9 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Architectural challenges
Symmetric MultiprocessingNoncoherent I/OOut-of-order I/OMemory management unitsMultiple ABIs
Multiple ISAsMultiple platformsTimekeeping
9 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Architectural challenges
Symmetric MultiprocessingNoncoherent I/OOut-of-order I/OMemory management unitsMultiple ABIsMultiple ISAs
Multiple platformsTimekeeping
9 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Architectural challenges
Symmetric MultiprocessingNoncoherent I/OOut-of-order I/OMemory management unitsMultiple ABIsMultiple ISAsMultiple platforms
Timekeeping
9 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Architectural challenges
Symmetric MultiprocessingNoncoherent I/OOut-of-order I/OMemory management unitsMultiple ABIsMultiple ISAsMultiple platformsTimekeeping
9 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Where to start
Copy from x86
Copy from ARMCopy from TileDo not copy at all!
10 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Where to start
Copy from x86
Copy from ARM
Copy from TileDo not copy at all!
10 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Where to start
Copy from x86Copy from ARM
Copy from Tile
Do not copy at all!
10 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Where to start
Copy from x86Copy from ARMCopy from Tile
Do not copy at all!
10 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Generic header files
42 versions of struct stat?
One minimal syscall list!Cover all the simple implementations
11 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Generic header files
42 versions of struct stat?One minimal syscall list!
Cover all the simple implementations
11 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Generic header files
42 versions of struct stat?One minimal syscall list!Cover all the simple implementations
11 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Generic Architecture template
Early Boot codezImage compressionLibrary functionsdevice treeTrap handlingSignal handlingptracepci
12 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
User space: runtime
glibc/eglibcuClibcklibc
13 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
User space: distro
Full distributionDebian, Fedora, OpenSUSE, Ubuntu, Gentoo, ...
Embedded distributionbuildrootyoctoemdebian
Busybox initramfs
14 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
User space: distro
Full distributionDebian, Fedora, OpenSUSE, Ubuntu, Gentoo, ...
Embedded distributionbuildrootyoctoemdebian
Busybox initramfs
14 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
User space: distro
Full distributionDebian, Fedora, OpenSUSE, Ubuntu, Gentoo, ...
Embedded distributionbuildrootyoctoemdebian
Busybox initramfs
14 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Lessons Learned
15 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Lesson #1
Start small
16 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Lesson #2
Generalize existing code for your special case
17 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Lesson #3
Understand the development process
18 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Lesson #4
Follow the upstream kernel
19 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Lesson #5
Debug your system with qemu with gdb
20 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Lesson #6
Simplify drivers using virtio and hvc
21 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Lesson #7
Describe SoC in a flattened device tree
22 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Lesson #8
Clean up after sparse and checkpatch
23 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Lesson #9
Run lockdep enabled kernels
24 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Lesson #10
Become a git master
25 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Legal Statement
This work represents the view of the author and does not necessarilyrepresent the view of IBM.IBM, IBM (logo), e-business (logo), pSeries, e (logo) server, andxSeries are trademarks or registered trademarks of InternationalBusiness Machines Corporation in the United States and/or othercountries.Linux is a registered trademark of Linus Torvalds.Other company, product, and service names may be trademarks orservice marks of others.
26 / 27 Arnd Bergmann c© 2010 IBM Corporation
Porting Linux to a new architecture, done right
Questions?
27 / 27 Arnd Bergmann c© 2010 IBM Corporation
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