A book teaching assembly language programming on the ARM 64 bit ISA

by elvis70 • 4 years ago

171 43 4 years ago

Sirened• 4 years ago

For all those learning (or even those who've learned :P), my favorite cheatsheet that I always pull up while writing ARMv8-A assembly is this one [1] from the University of Washington. ARMv8-A has a lot of fairly complex instructions and sometimes it's hard to remember all the odds and ends.

[1] https://courses.cs.washington.edu/courses/cse469/19wi/arm64....

ryao4• 4 years ago

Do you have one that can explain the operand syntax for the instructions that have operands starting with 'v' here:

https://gcc.godbolt.org/z/16a91n4zc

murderfs• 4 years ago

Those are NEON registers. v0.2d is the vector register v0, interpreted as two double words (i.e. two 64-bit elements).

ARM's documentation for this kind of thing is fairly good if you can find it: https://developer.arm.com/documentation/102474/0100/Fundamen...

PainfullyNormal2• 4 years ago

You will need to run a ARM Linux VM on the Macintosh - even on ARM-based Macs. Why? Apple. That's why.

I'm going to need a better answer than that. The whole reason I want to learn ARM is to get closer to the machine I'm actually using, not to get closer to a linux virtual machine that I will never use again running on the machine I'm actually using.

pmontra3• 4 years ago

https://github.com/below/HelloSilicon

PainfullyNormal2• 4 years ago

Oh, awesome. Thanks!

saagarjha• 4 years ago

Because they probably have Linux syscall numbers in their examples and those won’t work on macOS.

ryao4• 4 years ago

https://www.qemu.org/docs/master/user/main.html#linux-user-s...

QEMU can fix that.

canis-fam3• 4 years ago

Criticism appreciated.

Reasons are now explained in the README.

We promise a future chapter to bridge what is used elsewhere back to the Mac M1. And also, a chapter bridging to what is used on Windows ARM machines.

pmontra3• 4 years ago

Two notes to the author:

1. It would be nice to explain how to install an assembler (part of gcc?), how to run it on source code, how to run the program. Googled, not tested:

  as -o prog.o prog.s
  ld -o prog prog.o
  ./prog

2. Apparently GitHub accepts commits in the future because the last ones in this repo are timestamped Dec 23 2023.

masklinn2• 4 years ago

Apparently GitHub accepts commits in the future

Of course.

And this is made very annoying by github also insisting on reordering commits “chronologically” rather than topologically. If someone fucks up their local date (because they wanted to test something and forgot to reset it) you get a commit permanently pinned at the top of a branch until that date passes.

ryao4• 4 years ago

I am not the author, but I suspect qemu-user would be helpful here:

https://www.qemu.org/docs/master/user/main.html

He would just need to say how to get an assembler that would work. llvm-as might work, but I am not sure how to get it to produce code for another architecture offhand.

ptspts• 4 years ago

On my Ubuntu, there are many cross-assemblers (including ARM, RISC-V and PowerPC) and linkers available in packages. These packages have binutils in their name. Once installed, the assembler command has -as at the end of its name, and the linker has -ld there.

Kwpolska• 4 years ago

Why would GitHub prevent commits from the future? Git allows commit dates from the future and from before git was invented, and GitHub's job is to store git repositories.

pmontra3• 4 years ago

Locally git can't tell if the clock is in the future, unless it starts checking ntp servers or the like. However it's not its own business IMHO.

As a collaboration tool GitHub might refuse timestamps too much in the future, at least as an optional setting of the repository. If a coworker inadvertently moves the clock forward by an year when looking for the day of next new year eve, then makes a day worth of commits and pushes them, we'll have to delete those commits and make them again with the correct date.

canis-fam3• 4 years ago

Criticism appreciated.

The main README now contains install and build instructions.

The main body of the book will, over time, be updated to include build instructions for each example.

As per date... I'm at a loss. I believe my own machines are set correctly.

ryao4• 4 years ago

In fact, we would argue that the study of assembly language is extremely important to the building of competent software engineers. Further, we would argue that teaching the x86 instruction set is cruel as that ISA was born in the 1970s and has simply gotten more muddled with age.
The MIPS instruction set is another ISA that is often covered in College level courses. While kinder and gentler than the x86 ISA, the MIPS processor isn't nearly as relevant as the ARM family.

I disagree. My university taught me MIPS assembly and its only utility has been in enabling me to understand x86_64 assembly poorly. When I look at the disassembly of my code, it is in x86_64 assembly, yet I realized yesterday that I have no clue what the difference is between signed and unsigned subtraction on x86_64. Had that been covered in my university class, I would not be in a position where I need to reverse engineer how that works by working out the math based on the very succinct documentation.

I only recently dabbled with aarch64 and POWER9 because I felt inspired to try to make ZFS' fletcher4 checksum algorithm run faster on various architectures. I had no success on POWER9 due to the Talos II workstation being severely memory bandwidth limited, but had fairly good success on x86_64 and aarch64, although the PRs with that code are still works in progress.

A guide for NEON and SVE would be great, since that is the only aspect of the aarch64 assembly that I did not understand well enough to muddle through it in my recent fletcher4 adventures, but that does not appear to be here. Thankfully, Clang did an awesome job compiling GNU C dialect vector extensions into efficient, easy to understand NEON assembly (even if I had no clue about the notation used for registers), so I did not need to learn the syntax.

For students, I would suggest learning x86_64, since that is what they are going to be using and if they can learn that, they can learn just about any assembly language (although the RISC-V Vector Extension might pose some trouble). The broader industry shift from x86_64 to aarch64 is still years away and ARM seems determined to kill it before it is here by suing Qualcomm for wanting to build ARM processors under the license they already paid ARM to give them. ARM can say whatever they want in court, but at the end of the day, ARM IP now looks toxic. I hope RISC-V can take the baton from aarch64. It could very well be our only hope for a x86_64-free future given ARM's major strategic mistake.

masklinn2• 4 years ago

ARM seems determined to kill it before it is here by suing Qualcomm for wanting to build ARM processors under the license they already paid ARM to give them

That is not what they are doing at all and it’s very dishonest of you to pretend it is.

klelatti• 4 years ago

Indeed. I'm really surprised that some seem to be saying that Arm trying to enforce the terms of contracts freely entered into by two of its customers is a bad thing for the wider ecosystem.

billfruit2• 4 years ago

Is learning any sort of Assembly language a good investment of time? Is that time better spent more usefully studying other topics that help solve interesting problems?

Are there interesting problems that require knowledgeable of Assembly language to solve?

Would Dijsktra, for example have adviced teaching for or against teaching Assembly language?

sandruso2• 4 years ago

Understanding lower levels can be satisfying for certain type of people. I find it very useful when you can reason about stuff that is mostly invisible to other people. But if you are building web apps then this stuff is 95% useless as you can’t leverage the knowledge because web apps are much higher level.

If you are curious about this stuff definitely look into it. It may be worth to you.

flohofwoe2• 4 years ago

Any sort of serious optimization work may require mulling over disassembly listings of compiler output (at least after you've exhausted the 'simple' high level optimization options).

DiscoDays• 4 years ago

Is learning any sort of Assembly language a good investment of time?

Learning to understand Arm architecture specifically or computer architecture in general can be invaluable. A particular Assembly syntax is just a way of expressing what you want to do.

I would suggest reading a book about computer architecture or taking a course. And if you are like me and are interested in what complicated things hardware does to fulfil the needs of software, you might want to first read a book on operating systems (like OSTEP by Arpaci-Dusseaus, which is marvel of accessibility and challenge for students), because it will make you ask relevant question.

rramadass• 4 years ago

Would Dijsktra, for example have adviced teaching for or against teaching Assembly language?

Dijkstra makes a distinction between Computing Science and Computer Engineering. The former is the Theoretical Science part i.e. Mathematical Logic, Automata, Algorithms, Computability, Complexity etc. The latter is the design of practical machines where we can realize the running of algorithms from the former domain. Dijkstra did both but his interests/focus were more in the former domain.

However, he called the General-purpose Computer "A Radical Novelty" from the pov that it allowed us to do any computation that we can think of (subject to Mathematical limitations/Computability) unlike any other previous man-made inventions. Many of his EWDs talk about this. Given that Assembly language is the native language of a Computer and all Higher-level language abstraction constructs have to map to it there is great value in learning the structure of Assembly language and how to program using it. There is also the beauty of Engineering involved, where layers of abstraction come together in a harmonious manner to give you a Machine with almost limitless capabilities. Also note that Assembly language is the Computer Architecture view for a Programmer while Computer Organization is the engineering implementation of it.

The following two books are highly recommended for further understanding:

1) Code: The Hidden Language of Computer Hardware and Software by Charles Petzold.

2) Structured Computer Organization by Andrew Tanenbaum.

microtherion• 4 years ago

Writing assembly language is a rather specialized skill that few people need to master nowadays.

Being able to read it, on the other hand, I find really useful for debugging. You can follow execution into places where you don't have code at hand, find code that was not translated the way you expected (e.g. due to surprising aggressive optimizations), etc.

anta402• 4 years ago

> Are there interesting problems that require knowledgeable of Assembly language to solve?

If you find reverse engineering interesting, at minimum being able to read assembly is a must. I only learn assembly for fun, e.g writing SNES/Sega/Atari games.

As a mobile application developer, obviously assembly is practically useless for work.

celrod• 4 years ago

yet I realized yesterday that I have no clue what the difference is between signed and unsigned subtraction on x86_64

It's two's complement. There is no difference between signed and unsigned for addition, subtraction, or multiplication. https://en.m.wikipedia.org/wiki/Two%27s_complement

renox• 4 years ago

In the value no, in the condition code registers status, there may be differences.

uptakeinhibitor• 4 years ago

You might be interested in this repo that converts asmtutor to Arm64. It's not the most faithful port though:

https://github.com/lirorc/arm-asm-examples

boberoni• 4 years ago

I’m a noob at assembly and this was something that I never figured out:

For assembly languages, how does package management work? As an example, how would I “import” code from my co-worker or from an open source library on GitHub?

My first thought is that “maybe this is what a linker does…”, but what sort of toolchains exist for dependency management in assembly programming? What’s the analogy to pip, npm, cargo, etc.?

robinsonb5• 4 years ago

The idea of having dependency and package management system as an inherent part of a language's ecosystem is pretty new, and there isn't really any such thing even for C, let alone assembly language. So the short answer is "that's your problem", to solve however you wish! Personally I use git submodules.

AshamedCaptain• 4 years ago

Your operating system's package manager is the one going to do that.

flohofwoe2• 4 years ago

What’s the analogy to pip, npm, cargo, etc.?

mkdir and cp basically (or git submodules if you want to get fancy)

dboreham• 4 years ago

It's what the linker does.

shadowofneptune• 4 years ago

Even being able to use that assembly source as listed is not a guarantee. There's no standard macro language, even if two assemblers share most of their syntax. As other posts have said, binary compatibility is more important.

wyldfire• 4 years ago

The way you can interact with other code is via symbolic references. Indeed, the linker resolves most of these references. These are stored in an object file as a "relocation".

It's considerably less convenient than a package system.

anta402• 4 years ago

> What’s the analogy to pip, npm, cargo, etc.?

AFAIK no one build such convenient tool for assembly programming. So, simply put the the library codes inside your project folder, configure your Makefile/batch file, tell the linker where to find required .a/.lib files, etc.

More manual work, eh.

canis-fam3• 4 years ago

Thank you for the post here. Interest in the book has exploded.

I've already implemented some of the criticism written here. It is appreciated.

-- book's author

A book teaching assembly language programming on the ARM 64 bit ISA

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