LAS16-106: GNU Toolchain Development Lifecycle Speakers: Ryan Arnold Date: September 26, 2016 ★ Session Description ★ This presentation will examine the lifecycle of toolchain development from inception of the micro-architecture, to development of the ISA, to delivery of OS enablement in FOSS projects, to adoption in Linux Distributions. It will examine the behaviors of successful silicon vendors as well as behaviors of vendors that struggle to get their platform fully enabled in the GNU/Linux OS. ★ Resources ★ Etherpad: pad.linaro.org/p/las16-106 Presentations & Videos: http://connect.linaro.org/resource/las16/las16-106/ ★ Event Details ★ Linaro Connect Las Vegas 2016 – #LAS16 September 26-30, 2016 http://www.linaro.org http://connect.linaro.org

1. GNU Toolchain Lifecycle
Ryan S. Arnold

2. ENGINEERS AND DEVICES
WORKING TOGETHER

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A man builds a fine house; and now he has a master,
and a task for life; he is to furnish, watch, show it, and
keep it in repair, the rest of his days
- Ralph Waldo Emerson

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Wrong!

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GNU/Linux Distribution : (Distro) is a formally
supported collection of interoperable programs.
These programs have been quality and integration
tested in order to guarantee that they are compatible.

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http://www.ubuntu.com/info/release-end-of-life
https://wiki.ubuntu.com/LTS

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http://www.ubuntu.com/info/release-end-of-life
https://wiki.ubuntu.com/LTS

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https://access.redhat.com/articles/3078
https://access.redhat.com/support/policy/updates/errata/
RHEL6.0 GA 2010-11-09
RHEL6.8 - 2016-05-10
RHEL7.0 GA - 2014-06-09
RHEL7.2 - 2015-11-19 (AArch64)

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Protip: Submit Early & Submit
Often

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Toolchain Lifecycle - Linear Progression
● Idea conception (micro-
architecture)
● ISA
● KABI (contract with user-space)
● Kernel enablement
● Platform identification
● KABI implementation
● Kernel upstreaming
● ABI (binary contract between
programs)
● GNU Toolchain Implementation
● Platform identification
● ASM Instruction support
● Codegen
● Optimization
● GNU Toolchain Upstreaming
● Linux Distribution Adoption
● Customer’s Hands
● Linux Distro updates.

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Wrong!

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Idea
Conception
Distro
Adoption
Kernel
Enablement
Compiler
Enablement
Toolchain
Upstreaming

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Phases
● Phase 0 - Legal & Branding
● Phase 1 - Platform Enablement
● Phase 2 - ABI Enablement
● Phase 3 - Optimization
● Phase 4 - Distro Adoption

26. ENGINEERS AND DEVICES
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Phase 0 - Legal and Branding

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Danger! If your legal dept is dragging their feet on
approving upstream contribution your schedule is in
jeopardy.

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Phase 1 - Platform Enablement

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ISA - Instruction Set Architecture

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It is a cardinal sin to not implement all required
parts of the ISA

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Models

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Linux Kernel Platform Enablement

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www.kernel.org/category/releases.html

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Assembler, Linker & Compiler Microarch Identification

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GCC Instruction-Set & Cost Model

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Danger! Sometimes early enablement might give
away details of the processor, such as information
about the pipeline bandwidth.

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Glibc Platform Identification

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Protip: Get the KABI enablement code upstream as
soon as possible!

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Rev 1 Hardware

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Phase 3 - ABI Enablement

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Using The Existing ABI

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Danger! You implemented all required parts of the ISA
right? If not, you’ve defined a new ABI that you have
to implement.

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Protip: Don’t use an ABI change as a way to squeeze
out more performance (unless it benefits all
microarch variants)

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New ABI? Really?

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It is a cardinal sin to release binaries compiled with
a pre-release ABI into the wild.

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Danger! Just because you proposed the change
doesn’t mean you get to own the ABI.

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GCC, Linker, and Assembler ABI Changes

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Listen to your patch reviewers and implement
changes requested or your update patches will be
ignored.

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Danger! If you don’t respect the opinion of the person
who will be maintaining your software, then your
contribution isn’t going to be respected.

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Protip: Drop what you’re doing and turn around a
patch re-spin as soon as possible after a maintainer
has reviewed your patch.

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Protip: You might be asked to implement a generic
solution in place of a number of arch-specific
implementations. Do it!

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Glibc ABI Changes

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If you’re implementing a glibc ABI change/addition
you need a complete release cycle for evaluation.

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Phase 3 - Upstreaming Optimizations

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GCC Optimizations

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Glibc Optimizations & IFUNC

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Phase 4 - Distro Adoption

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A man builds a fine house; and now he has a master,
and a task for life; he is to furnish, watch, show it, and
keep it in repair, the rest of his days
- Ralph Waldo Emerson

64. Thank You
#LAS16
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