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<!DOCTYPE html>
<!--
Copyright 2010 Google Inc.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
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http://www.apache.org/licenses/LICENSE-2.0
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distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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limitations under the License.
Original slides: Marcin Wichary (mwichary@google.com)
Modifications: Ernest Delgado (ernestd@google.com)
Alex Russell (slightlyoff@chromium.org)
landslide modifications: Adam Zapletal (adamzap@gmail.com)
Nicolas Perriault (nperriault@gmail.com)
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<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<title>Assembly in Go</title>
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<!-- slide source: GoAsm.rst -->
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<header><h1>Assembly in Go</h1></header>
</div>
<div class="presenter_notes">
<header><h1>Presenter Notes</h1></header>
<section>
</section>
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<footer>
<aside class="source">
Source: <a href="GoAsm.rst">GoAsm.rst</a>
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1/19
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<header><h1>Why use Assembly in Go?</h1></header>
<section><p>Pros:</p>
<ul class="simple">
<li>Speed up computationally intensive functions.</li>
<li>Access CPU specific instructions or capabilities that are not available otherwise.</li>
<li>Good way to learn and play around with assembly.</li>
<li>go vet works on assembly files.</li>
</ul>
<p>Cons:</p>
<ul class="simple">
<li>Very hard to write bug-free, safe and stable code.</li>
<li>Binds your code to the CPU architectures you have written assembly for (unless a fallback function written in go is created. More on this later).</li>
<li>It may breake in the future if go shanges internaly.</li>
<li>Currently the functions written in assembly will not be inlined like small go functions.</li>
<li>It will not be covered by the go tool cover.</li>
<li>It will not work with go fmt.</li>
</ul></section>
</div>
<div class="presenter_notes">
<header><h1>Presenter Notes</h1></header>
<section>
</section>
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<footer>
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Source: <a href="GoAsm.rst">GoAsm.rst</a>
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<aside class="page_number">
2/19
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<header><h1>How it works</h1></header>
<section><p>There is no inlining of assembly code in a go file.</p>
<p>Special names for the assembly files (_386.s, _amd64.s, _arm.s).</p>
<p>Declare the assembly function in the go code.</p></section>
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<header><h1>Presenter Notes</h1></header>
<section>
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Source: <a href="GoAsm.rst">GoAsm.rst</a>
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<aside class="page_number">
3/19
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<header><h1>The assembly function decleration</h1></header>
<section><p>Special character for function declerations in the .s files</p>
<p>Middle dot: · (Unicode code point U+00B7)</p>
<p>Example:</p>
<p>TEXT ·Test(SB), 7, $0</p></section>
</div>
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<header><h1>Presenter Notes</h1></header>
<section>
</section>
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4/19
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<header><h1>Before using Assembly in Go</h1></header>
<section><p>Have you tried...</p>
<ul class="simple">
<li>Identifying what the program is spending most time on by profiling?</li>
<li>Algoritmic optimizations if it is applicable?</li>
<li>Minimise the generation of garbage? (conversions from string to byte slice and vice versa etc.)</li>
<li>Finding a good library that already solved this problem?</li>
</ul>
<p>If nothing else works then you can consider rewriting in parts or as a
whole the computationaly intence function in optimized assembly.</p></section>
</div>
<div class="presenter_notes">
<header><h1>Presenter Notes</h1></header>
<section>
</section>
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<footer>
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Source: <a href="GoAsm.rst">GoAsm.rst</a>
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<aside class="page_number">
5/19
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<!-- slide source: GoAsm.rst -->
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<header><h1>Before writing Assembly in Go</h1></header>
<section><ul class="simple">
<li>Write test cases for every possible variation of input (there are too many pitfalls to do anything else).</li>
</ul>
<p>Alignment, Page boundaries, Overflows, Special cases etc.</p></section>
</div>
<div class="presenter_notes">
<header><h1>Presenter Notes</h1></header>
<section>
</section>
</div>
<footer>
<aside class="source">
Source: <a href="GoAsm.rst">GoAsm.rst</a>
</aside>
<aside class="page_number">
6/19
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<!-- slide source: GoAsm.rst -->
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<header><h1>Syntax</h1></header>
<section><p>[Instruction] [src], [dst]</p>
<p>Immediate values:</p>
<ul class="simple">
<li>MOVQ $1234, AX //; moves 1234 in to AX</li>
<li>MOVQ $0x12EF, AX //; moves the hex value 0x12EF in to AX</li>
</ul>
<p>Size of the operands:</p>
<ul class="simple">
<li>MOVQ is a MOV of size Quad word (8 byte)</li>
<li>MOVL is a MOV of size Double word or Long word (4 byte)</li>
<li>MOVW is a MOV of size Word (2 byte)</li>
<li>MOVB is a MOV of size Byte (1 byte)</li>
</ul>
<p>Registers:</p>
<ul class="simple">
<li>SP, AX, BX, CX, DX, BP, DI, SI, R8-R15</li>
<li>X0-X15 (XMM registers - 16 byte)</li>
<li>M0-M7 (MMX registers - 8 byte)</li>
</ul></section>
</div>
<div class="presenter_notes">
<header><h1>Presenter Notes</h1></header>
<section>
</section>
</div>
<footer>
<aside class="source">
Source: <a href="GoAsm.rst">GoAsm.rst</a>
</aside>
<aside class="page_number">
7/19
</aside>
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<!-- slide source: GoAsm.rst -->
<div class="slide-wrapper">
<div class="slide">
<div class="inner">
<header><h1>More Syntax</h1></header>
<section><p>Addressing:</p>
<ul class="simple">
<li>AX, (AX), (AX)(BX*4), 10(AX), and 10(AX)(BX*4)</li>
</ul>
<p>The offsets from AX can be replaced by offsets from FP or SB to access names:</p>
<ul class="simple">
<li>extern+5(SB)(AX*2)</li>
</ul>
<p>Examples:</p>
<p>MOVQ AX, BX //; Move the value of AX in to BX</p>
<p>MOVQ (AX), BX //; Move 8 bytes from where AX is pointing in to BX</p>
<p>MOVQ (AX)(BX*4), CX //; Move 8 bytes from where AX + 4*BX is pointing</p>
<p>MOVQ 10(AX)(BX*4), CX //; Move 8 bytes from where AX + 4*BX + 10 is pointing</p>
<p>MOVQ asdf+0(FP), AX //; Move the first 8 bytes located at the Frame pointer in to AX.</p>
<p>//; This is usualy the first argument, or part of the first argument to a function.</p>
<p>//; asdf in this case is just a lable for conviniance.</p></section>
</div>
<div class="presenter_notes">
<header><h1>Presenter Notes</h1></header>
<section>
</section>
</div>
<footer>
<aside class="source">
Source: <a href="GoAsm.rst">GoAsm.rst</a>
</aside>
<aside class="page_number">
8/19
</aside>
</footer>
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</div>
<!-- slide source: GoAsm.rst -->
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<header><h1>More Documentation and examples</h1></header>
<section><p>Docs:</p>
<p><a class="reference external" href="http://plan9.bell-labs.com/sys/doc/asm.html">http://plan9.bell-labs.com/sys/doc/asm.html</a></p>
<p><a class="reference external" href="http://golang.org/doc/asm">http://golang.org/doc/asm</a></p>
<p><a class="reference external" href="http://www.doxsey.net/blog/go-and-assembly/index.htm">http://www.doxsey.net/blog/go-and-assembly/index.htm</a></p>
<p>Examples (all .s files for the architecture you are interested in):</p>
<p><a class="reference external" href="http://golang.org/src/pkg/math/">http://golang.org/src/pkg/math/</a></p>
<p><a class="reference external" href="http://golang.org/src/pkg/runtime/">http://golang.org/src/pkg/runtime/</a></p>
<p><a class="reference external" href="http://golang.org/src/pkg/crypto/aes/">http://golang.org/src/pkg/crypto/aes/</a></p>
<p><a class="reference external" href="http://golang.org/src/pkg/crypto/md5/">http://golang.org/src/pkg/crypto/md5/</a></p>
<p><a class="reference external" href="http://golang.org/src/pkg/crypto/sha1/">http://golang.org/src/pkg/crypto/sha1/</a></p>
<p><a class="reference external" href="http://golang.org/src/pkg/crypto/rc4/">http://golang.org/src/pkg/crypto/rc4/</a></p></section>
</div>
<div class="presenter_notes">
<header><h1>Presenter Notes</h1></header>
<section>
</section>
</div>
<footer>
<aside class="source">
Source: <a href="GoAsm.rst">GoAsm.rst</a>
</aside>
<aside class="page_number">
9/19
</aside>
</footer>
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</div>
<!-- slide source: GoAsm.rst -->
<div class="slide-wrapper">
<div class="slide">
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<header><h1>Starting Point</h1></header>
<section><p>Usually when optimising a function you already have the function written in go,
if this is the case you can easely get a good starting point for your assembly
by outputing the compiler generated assembly for the function.</p>
<p>go tool 6g -S gofile.go</p></section>
</div>
<div class="presenter_notes">
<header><h1>Presenter Notes</h1></header>
<section>
</section>
</div>
<footer>
<aside class="source">
Source: <a href="GoAsm.rst">GoAsm.rst</a>
</aside>
<aside class="page_number">
10/19
</aside>
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<!-- slide source: GoAsm.rst -->
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<header><h1>Ok lets start with a basic example</h1></header>
</div>
<div class="presenter_notes">
<header><h1>Presenter Notes</h1></header>
<section>
</section>
</div>
<footer>
<aside class="source">
Source: <a href="GoAsm.rst">GoAsm.rst</a>
</aside>
<aside class="page_number">
11/19
</aside>
</footer>
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</div>
<!-- slide source: GoAsm.rst -->
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<header><h1>typehack.go</h1></header>
<section><pre><span class="kn">package</span> <span class="nx">typehack</span>
<span class="c1">// ToByteSlice returns the string s as a []byte. Note that cap in bs is</span>
<span class="c1">// set to the length of s. WARNING! bs uses the same memory as s and has</span>
<span class="c1">// therefore broken the immutability of the string s. This can lead to</span>
<span class="c1">// serious bugs, vulnerabilities or other errors if used incorrectly.</span>
<span class="kd">func</span> <span class="nx">ToByteSlice</span><span class="p">(</span><span class="nx">s</span> <span class="kt">string</span><span class="p">)</span> <span class="p">(</span><span class="nx">bs</span> <span class="p">[]</span><span class="kt">byte</span><span class="p">)</span>
<span class="c1">// ToString returns the []byte bs as a string. Note that the cap value</span>
<span class="c1">// from bs is discarded. WARNING! s uses the same memory as bs and is</span>
<span class="c1">// therfor not Immutable. This can lead to serious bugs, vulnerabilities</span>
<span class="c1">// or other errors if used incorrectly.</span>
<span class="kd">func</span> <span class="nx">ToString</span><span class="p">(</span><span class="nx">bs</span> <span class="p">[]</span><span class="kt">byte</span><span class="p">)</span> <span class="p">(</span><span class="nx">s</span> <span class="kt">string</span><span class="p">)</span>
<span class="c1">// Fallback for not supported architectures</span>
<span class="kd">func</span> <span class="nx">toByteSlice</span><span class="p">(</span><span class="nx">s</span> <span class="kt">string</span><span class="p">)</span> <span class="p">(</span><span class="nx">bs</span> <span class="p">[]</span><span class="kt">byte</span><span class="p">)</span> <span class="p">{</span>
<span class="k">return</span> <span class="p">[]</span><span class="nb">byte</span><span class="p">(</span><span class="nx">s</span><span class="p">)</span>
<span class="p">}</span>
<span class="c1">// Fallback for not supported architectures</span>
<span class="kd">func</span> <span class="nx">toString</span><span class="p">(</span><span class="nx">bs</span> <span class="p">[]</span><span class="kt">byte</span><span class="p">)</span> <span class="p">(</span><span class="nx">s</span> <span class="kt">string</span><span class="p">)</span> <span class="p">{</span>
<span class="k">return</span> <span class="nb">string</span><span class="p">(</span><span class="nx">bs</span><span class="p">)</span>
</pre>
<p>}</p></section>
</div>
<div class="presenter_notes">
<header><h1>Presenter Notes</h1></header>
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<header><h1>example_test.go - ToByteSlice</h1></header>
<section><pre><span class="c1">//; func ToByteSlice(s string) (bs []byte)</span>
<span class="nx">TEXT</span> <span class="err">·</span><span class="nx">ToByteSlice</span><span class="p">(</span><span class="nx">SB</span><span class="p">),</span><span class="mi">7</span><span class="p">,</span><span class="err">$</span><span class="mi">0</span>
<span class="c1">// s+0(FP) contains pointer to the s data</span>
<span class="c1">// s+8(FP) contains length of s</span>
<span class="c1">// bs+16(FP) contains pointer to bs data</span>
<span class="c1">// bs+24(FP) contains length of bs</span>
<span class="c1">// bs+32(FP) contains cap of bs</span>
<span class="c1">//; Pointer to data in s is moved to bs pointer so that bs now refers to</span>
<span class="c1">//; the same data.</span>
<span class="nx">MOVQ</span> <span class="nx">s</span><span class="o">+</span><span class="mi">0</span><span class="p">(</span><span class="nx">FP</span><span class="p">),</span> <span class="nx">AX</span>
<span class="nx">MOVQ</span> <span class="nx">s</span><span class="o">+</span><span class="mi">8</span><span class="p">(</span><span class="nx">FP</span><span class="p">),</span> <span class="nx">BX</span>
<span class="nx">MOVQ</span> <span class="nx">AX</span><span class="p">,</span> <span class="nx">bs</span><span class="o">+</span><span class="mi">16</span><span class="p">(</span><span class="nx">FP</span><span class="p">)</span>
<span class="nx">MOVQ</span> <span class="nx">BX</span><span class="p">,</span> <span class="nx">bs</span><span class="o">+</span><span class="mi">24</span><span class="p">(</span><span class="nx">FP</span><span class="p">)</span>
<span class="nx">MOVQ</span> <span class="nx">BX</span><span class="p">,</span> <span class="nx">bs</span><span class="o">+</span><span class="mi">32</span><span class="p">(</span><span class="nx">FP</span><span class="p">)</span>
<span class="nx">RET</span>
</pre></section>
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<div class="presenter_notes">
<header><h1>Presenter Notes</h1></header>
<section>
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<header><h1>example_test.go - ToString</h1></header>
<section><pre><span class="c1">//; func ToString(bs []byte) (s string)</span>
<span class="nx">TEXT</span> <span class="err">·</span><span class="nx">ToString</span><span class="p">(</span><span class="nx">SB</span><span class="p">),</span><span class="mi">7</span><span class="p">,</span><span class="err">$</span><span class="mi">0</span>
<span class="c1">// bs+0(FP) contains pointer to the bs data</span>
<span class="c1">// bs+8(FP) contains length of bs</span>
<span class="c1">// bs+16(FP) contains cap of bs</span>
<span class="c1">// s+24(FP) contains pointer to s data</span>
<span class="c1">// s+32(FP) contains length of s</span>
<span class="c1">//; Pointer to data in bs is moved to s pointer so that bs now refers to</span>
<span class="c1">//; the same data.</span>
<span class="nx">MOVQ</span> <span class="nx">bs</span><span class="o">+</span><span class="mi">0</span><span class="p">(</span><span class="nx">FP</span><span class="p">),</span> <span class="nx">AX</span>
<span class="nx">MOVQ</span> <span class="nx">bs</span><span class="o">+</span><span class="mi">8</span><span class="p">(</span><span class="nx">FP</span><span class="p">),</span> <span class="nx">BX</span>
<span class="nx">MOVQ</span> <span class="nx">AX</span><span class="p">,</span> <span class="nx">s</span><span class="o">+</span><span class="mi">24</span><span class="p">(</span><span class="nx">FP</span><span class="p">)</span>
<span class="nx">MOVQ</span> <span class="nx">BX</span><span class="p">,</span> <span class="nx">s</span><span class="o">+</span><span class="mi">32</span><span class="p">(</span><span class="nx">FP</span><span class="p">)</span>
<span class="nx">RET</span>
</pre></section>
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<header><h1>Presenter Notes</h1></header>
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<header><h1>Side Note</h1></header>
<section><p>To get more information on how the internal structure of []byte and strings please visit:</p>
<p><a class="reference external" href="http://blog.golang.org/go-slices-usage-and-internals">http://blog.golang.org/go-slices-usage-and-internals</a></p></section>
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<header><h1>Presenter Notes</h1></header>
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<header><h1>Fallback for 386 and ARM</h1></header>
<section><p>typehack_arm.s:</p>
<pre><span class="c1">//; func ToByteSlice(s string) (bs []byte)</span>
<span class="nx">TEXT</span> <span class="err">·</span><span class="nx">ToByteSlice</span><span class="p">(</span><span class="nx">SB</span><span class="p">),</span><span class="nx">NOSPLIT</span><span class="p">,</span><span class="err">$</span><span class="mi">0</span>
<span class="nx">B</span> <span class="err">·</span><span class="nx">toByteSlice</span><span class="p">(</span><span class="nx">SB</span><span class="p">)</span>
<span class="c1">//; func ToString(bs []byte) (s string)</span>
<span class="nx">TEXT</span> <span class="err">·</span><span class="nx">ToString</span><span class="p">(</span><span class="nx">SB</span><span class="p">),</span><span class="nx">NOSPLIT</span><span class="p">,</span><span class="err">$</span><span class="mi">0</span>
<span class="nx">B</span> <span class="err">·</span><span class="nx">toString</span><span class="p">(</span><span class="nx">SB</span><span class="p">)</span>
</pre>
<p>typehack_386.s:</p>
<pre><span class="c1">//; func ToByteSlice(s string) (bs []byte)</span>
<span class="nx">TEXT</span> <span class="err">·</span><span class="nx">ToByteSlice</span><span class="p">(</span><span class="nx">SB</span><span class="p">),</span><span class="nx">NOSPLIT</span><span class="p">,</span><span class="err">$</span><span class="mi">0</span>
<span class="nx">JMP</span> <span class="err">·</span><span class="nx">toByteSlice</span><span class="p">(</span><span class="nx">SB</span><span class="p">)</span>
<span class="c1">//; func ToString(bs []byte) (s string)</span>
<span class="nx">TEXT</span> <span class="err">·</span><span class="nx">ToString</span><span class="p">(</span><span class="nx">SB</span><span class="p">),</span><span class="nx">NOSPLIT</span><span class="p">,</span><span class="err">$</span><span class="mi">0</span>
<span class="nx">JMP</span> <span class="err">·</span><span class="nx">toString</span><span class="p">(</span><span class="nx">SB</span><span class="p">)</span>
</pre></section>
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<header><h1>Presenter Notes</h1></header>
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<header><h1>example_test.go</h1></header>
<section><pre><span class="kn">package</span> <span class="nx">typehack_test</span>
<span class="kn">import</span> <span class="s">"fmt"</span>
<span class="kn">import</span> <span class="nx">typehack</span> <span class="s">"."</span>
<span class="kd">func</span> <span class="nx">ExampleToByteSlice</span><span class="p">()</span> <span class="p">{</span>
<span class="nx">s</span> <span class="o">:=</span> <span class="s">"Hello, Gophers!"</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"ToByteSlice:"</span><span class="p">,</span> <span class="nx">typehack</span><span class="p">.</span><span class="nx">ToByteSlice</span><span class="p">(</span><span class="nx">s</span><span class="p">))</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"Raw s:"</span><span class="p">,</span> <span class="nx">s</span><span class="p">)</span>
<span class="c1">// Output:</span>
<span class="c1">// ToByteSlice: [72 101 108 108 111 44 32 71 111 112 104 101 114 115 33]</span>
<span class="c1">// Raw s: Hello, Gophers!</span>
<span class="p">}</span>
<span class="kd">func</span> <span class="nx">ExampleToString</span><span class="p">()</span> <span class="p">{</span>
<span class="nx">bs</span> <span class="o">:=</span> <span class="p">[]</span><span class="nb">byte</span><span class="p">(</span><span class="s">"Hello, Gophers!"</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"ToString:"</span><span class="p">,</span> <span class="nx">typehack</span><span class="p">.</span><span class="nx">ToString</span><span class="p">(</span><span class="nx">bs</span><span class="p">))</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"Raw bs:"</span><span class="p">,</span> <span class="nx">bs</span><span class="p">)</span>
<span class="c1">// Output:</span>
<span class="c1">// ToString: Hello, Gophers!</span>
<span class="c1">// Raw bs: [72 101 108 108 111 44 32 71 111 112 104 101 114 115 33]</span>
<span class="p">}</span>
</pre></section>
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<header><h1>Other examples</h1></header>
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<header><h1>Presenter Notes</h1></header>
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<header><h1>Thank you!</h1></header>
<section><p>Go Stockholm Meetup</p>
<p>23 May 2014</p>
<p>Daniel Lidén</p></section>
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<div id="toc" class="sidebar hidden">
<h2>Table of Contents</h2>
<table>
<caption>Table of Contents</caption>
<tr id="toc-row-1">
<th><a href="#slide1">Assembly in Go</a></th>
<td><a href="#slide1">1</a></td>
</tr>
<tr id="toc-row-2">
<th><a href="#slide2">Why use Assembly in Go?</a></th>
<td><a href="#slide2">2</a></td>
</tr>
<tr id="toc-row-3">
<th><a href="#slide3">How it works</a></th>
<td><a href="#slide3">3</a></td>
</tr>
<tr id="toc-row-4">
<th><a href="#slide4">The assembly function decleration</a></th>
<td><a href="#slide4">4</a></td>
</tr>
<tr id="toc-row-5">
<th><a href="#slide5">Before using Assembly in Go</a></th>
<td><a href="#slide5">5</a></td>
</tr>
<tr id="toc-row-6">
<th><a href="#slide6">Before writing Assembly in Go</a></th>
<td><a href="#slide6">6</a></td>
</tr>
<tr id="toc-row-7">
<th><a href="#slide7">Syntax</a></th>
<td><a href="#slide7">7</a></td>
</tr>
<tr id="toc-row-8">
<th><a href="#slide8">More Syntax</a></th>
<td><a href="#slide8">8</a></td>
</tr>
<tr id="toc-row-9">
<th><a href="#slide9">More Documentation and examples</a></th>
<td><a href="#slide9">9</a></td>
</tr>
<tr id="toc-row-10">
<th><a href="#slide10">Starting Point</a></th>
<td><a href="#slide10">10</a></td>
</tr>
<tr id="toc-row-11">
<th><a href="#slide11">Ok lets start with a basic example</a></th>
<td><a href="#slide11">11</a></td>
</tr>
<tr id="toc-row-12">
<th><a href="#slide12">typehack.go</a></th>
<td><a href="#slide12">12</a></td>
</tr>
<tr id="toc-row-13">
<th><a href="#slide13">example_test.go - ToByteSlice</a></th>
<td><a href="#slide13">13</a></td>
</tr>
<tr id="toc-row-14">
<th><a href="#slide14">example_test.go - ToString</a></th>
<td><a href="#slide14">14</a></td>
</tr>
<tr id="toc-row-15">
<th><a href="#slide15">Side Note</a></th>
<td><a href="#slide15">15</a></td>
</tr>
<tr id="toc-row-16">
<th><a href="#slide16">Fallback for 386 and ARM</a></th>
<td><a href="#slide16">16</a></td>
</tr>
<tr id="toc-row-17">
<th><a href="#slide17">example_test.go</a></th>
<td><a href="#slide17">17</a></td>
</tr>
<tr id="toc-row-18">
<th><a href="#slide18">Other examples</a></th>
<td><a href="#slide18">18</a></td>
</tr>
<tr id="toc-row-19">
<th><a href="#slide19">Thank you!</a></th>
<td><a href="#slide19">19</a></td>
</tr>
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