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davel ,
@davel@lemmy.ml avatar

Assembly code is for writing C compilers, and C compilers are for writing Lisp interpreters.

henfredemars ,

I saw a Scheme interpreter written in assembly running a C compiler written in Scheme.

davel ,
@davel@lemmy.ml avatar

https://lemmy.ml/pictrs/image/2b1e1b92-c532-4381-8498-e02fb3697156.jpeg

henfredemars , (edited )

There’s actually good reasons for this design. It’s easy to write a Scheme interpreter in assembly, but it’s hard to write a C compiler in assembly that handles everything correctly. Much rather write it in higher level language if possible and Scheme lowers the bar to getting there, so you can get away from using assembly as quickly as possible. Or you can copy somebody else’s Scheme implementation of a C compiler because now you’re platform independent.

Then you can write your C compiler in C (or steal a better compiler already written in C) and close the loop. For your final step, you use the C compiler to compile itself.

wewbull ,

Only the most very basic compilers. C compilers are in C mainly.

davel ,
@davel@lemmy.ml avatar

Not the first C compiler obviously. According to this Stack Overflow post, BCPL* begat B, which begat C. Language self-hosting is pretty fascinating.

*Perhaps BCPL was originally written in assembly; I’m not certain: github.com/SergeGris/BCPL-compiler

ulterno ,
@ulterno@lemmy.kde.social avatar

Talking about bootstrap here?

wewbull ,

Indeed

Revan343 ,

And that’s how you get the Thompson hack

RestrictedAccount ,

Back in High School in the 80’s me and a buddy wrote a Z-80 editor assembler in TRS-DOS BASIC.

It was not rocket science.

davel ,
@davel@lemmy.ml avatar

I never did get very far with the TRS-80 Editor Assembler, but that was my first exposure to such things.

I also remember the BASIC code for the Dancing Daemon which was replete with PEEKs and POKEs, such that much of it was written in machine code.

nobleshift ,
@nobleshift@lemmy.world avatar

https://lemmy.world/pictrs/image/353208bf-405a-4f59-999c-4eb0be766c27.jpeg

SpaceNoodle ,

Mebly I do, and mebly I don’t.

sag OP ,

I have Dyslexia ¯_(ツ)_/¯ Sorry.

lord_ryvan ,

You dropped this \

Short explanation: Type ¯\_(ツ)_/¯ to see ¯_(ツ)_/¯.

Long expanation: Lemmy supports formatting, like italic becomes italic. To stop this from happening, you can put a \ before it like _; the \ isn’t shown. This is why ¯_(ツ)/¯ becomes ¯(ツ)/¯. To show a \ you need an additional \ like so: \, and to make sure _ is shown and not turned into italic, it too needs . This is why ¯\_(ツ)_/¯ becomes ¯_(ツ)/¯

ulterno ,
@ulterno@lemmy.kde.social avatar

Alternatively, you can just use the `` enclosure, used for single line code.
That is a “grave accent” or a “backtick”, the key you will find on the left of the ‘1’ key and under the ‘Esc’ key on a standard (ISO, maybe) 104/105 key qwerty keyboard.

¯_(ツ)_/¯

AnUnusualRelic ,
@AnUnusualRelic@lemmy.world avatar

The backslash is known as an escape character in this context, because it removes (escapes) the special meaning of the following character.

It’s also used that way in most Unix shells.

theneverfox ,
@theneverfox@pawb.social avatar

I’m sorry, I have no idea what you’re talking about. Could you explain it in assembly?

lord_ryvan , 

<span style="color:#323232;">global _main
</span><span style="color:#323232;">    extern  _GetStdHandle@4
</span><span style="color:#323232;">    extern  _WriteFile@20
</span><span style="color:#323232;">    extern  _ExitProcess@4
</span><span style="color:#323232;">
</span><span style="color:#323232;">    section .text
</span><span style="color:#323232;">_main:
</span><span style="color:#323232;">    ; DWORD  bytes;    
</span><span style="color:#323232;">    mov     ebp, esp
</span><span style="color:#323232;">    sub     esp, 4
</span><span style="color:#323232;">
</span><span style="color:#323232;">    ; hStdOut = GetstdHandle( STD_OUTPUT_HANDLE)
</span><span style="color:#323232;">    push    -11
</span><span style="color:#323232;">    call    _GetStdHandle@4
</span><span style="color:#323232;">    mov     ebx, eax    
</span><span style="color:#323232;">
</span><span style="color:#323232;">    ; WriteFile( hstdOut, message, length(message), &bytes, 0);
</span><span style="color:#323232;">    push    0
</span><span style="color:#323232;">    lea     eax, [ebp-4]
</span><span style="color:#323232;">    push    eax
</span><span style="color:#323232;">    push    (message_end - message)
</span><span style="color:#323232;">    push    message
</span><span style="color:#323232;">    push    ebx
</span><span style="color:#323232;">    call    _WriteFile@20
</span><span style="color:#323232;">
</span><span style="color:#323232;">    ; ExitProcess(0)
</span><span style="color:#323232;">    push    0
</span><span style="color:#323232;">    call    _ExitProcess@4
</span><span style="color:#323232;">
</span><span style="color:#323232;">    ; never here
</span><span style="color:#323232;">    hlt
</span><span style="color:#323232;">message:
</span><span style="color:#323232;">    db      '¯\_(ツ)_/¯', 10
</span><span style="color:#323232;">message_end:
</span>
lightscription , (edited )

Do you want to show us what that looks like in assembly, ASCII from machine code? …ha, ha, ha, no!

Depends on the device, I know. Such a pain without the higher level languages.

What would it look like for ARM android touch screens? Just for one character…

But if some characters go missing or are exchanged for others for no discernable reason, then might that be an exploit on a EC or assembly level?

JoMiran ,
@JoMiran@lemmy.ml avatar

In college back in 1991. Also had to do PASCAL and FORTRAN but thankfully those two were in a single course.

expatriado ,

I also took PASCAL in the 90s, but it is considered a high level language, and writes similarly to other high lvl languages, assembly has a very different syntax

JoMiran ,
@JoMiran@lemmy.ml avatar

Oh, I know. I meant that we had to take courses on older languages as part of the curriculum. That was a funky little college program. The oddest experience for me was taking Python back in the day as the “new thing” then not seeing it again until it absolutely exploded ~10 years ago. That program is also why I ended up playing with Linux so early on. The professors truly seemed to have a passion for emerging technologies while not wanting anyone to forget what came before. Thankfully, no punch cards.

thejml ,

We used turbo pascal in school in the early 90’s. And it had assembly blocks… which I used copious amounts of because it was the only way to make the IBM PS/1’s do useful graphics.

finley ,

I remember watching assembly demos in the early-mid 90s and thinking those guys were wizards

gens ,

Pouet.net

JoYo ,
@JoYo@lemmy.ml avatar

I get the feeling that all of these assembly jokes are justifications to avoid learning assembly.

You can still make syscalls in assembly. Assembly isnt magic. It isn’t starting from the creation of matter and energy, it’s just very specific code.

NocturnalMorning ,

It’s just a joke friend.

MadhuGururajan ,

A very bad one if it requires switching off a large portion of your brain to find it funny.

Arsecroft ,
@Arsecroft@lemmy.sdf.org avatar

7597

JoYo ,
@JoYo@lemmy.ml avatar

I said so in my comment, try to keep up.

NocturnalMorning ,

I learned assembly for a few weeks when I first started a new job once (didn’t even have anything to do with my job), and I always felt like my brain was tired after trying to write in assembly. Just took so much more mental concentration than writing in c for example.

Cysioland ,
@Cysioland@lemmygrad.ml avatar

Assembly was easier to me than C/C++.

skullgiver ,
@skullgiver@popplesburger.hilciferous.nl avatar

Assembly isn’t that hard. It’s the same imperative programming, but more verbose, more work, and more random names and patterns to remember. If you can understand “x += 3 is the same as x = x + 3”, you can understand how the add instruction works.

I wouldn’t be able to write Rollercoaster Tycoon in assembly because keeping track of all that code in assembly files must be hell, but people pretending like you need to be some kind of wizard to write assembly code are exaggerating.

These days, you won’t be able to beat the compiler even if you wrote your code in assembly, maybe with the exception of bespoke SIMD algorithms. Writing assembly is something only kernel developers and microcontroller developers may need to do in their day to day life.

Reading assembly is still a valuable skill, though, especially if you come anywhere near native code. What you think you wrote and what the CPU is actually trying to do may not be the same, and a small bit of manual debugging work can help you get started resolving crashes that make no sense whatsoever. No need to remember thousands of instructions either, 99% of assembly code is just variations of copying memory, checking equality and jumping anyway. Look up the weird assembly instructions your disassembler spits out, they’re documented very well.

leisesprecher ,

Assembly is hard, because you need to understand your problem on multiple levels and get absolute zero guidance by compilers.

Even C guides you a tiny bit and takes away some of the low level details, so you have more mental capacity to actually solve your problem.

Oh, and you have a standard library. Assembly seems to involve solving everything yourself. No simple function call to truncate a string or turn a char array to uppercase.

gens ,

Missing “;” on line 148.

skullgiver ,
@skullgiver@popplesburger.hilciferous.nl avatar

Unless you’re developing an OS or something, you’ll probably be using the C standard library and maybe a bunch of other libraries provided by most distros. Just because you’re doing assembly doesn’t mean you need to program syscalls manually.

Modern assemblers also come with plenty of macros to prevent common mistakes and provide common methods. For instance. NASM comes with things like %strcat to do string concatenation.

I suppose the lack of compiler warnings can be a challenge, but most low-level compilers don’t exactly provide guidance for when you design your program wrong.

No doubt Assembly is harder than Java or Python, but compared to languages like C, I don’t think it’s as hard as people pretend to it to be.

CanadaPlus ,

I wouldn’t be able to write Rollercoaster Tycoon in assembly because keeping track of all that code in assembly files must be hell, but people pretending like you need to be some kind of wizard to write assembly code are exaggerating.

Well, they’ve got a point for the bigger machine codes. Just the barebones specification for x86 is a doorstopper IIRC.

From what I’ve heard, writing big stuff in assembly comes down to play-acting the compiler yourself on paper, essentially.

skullgiver ,
@skullgiver@popplesburger.hilciferous.nl avatar

From what I’ve heard, writing big stuff in assembly comes down to play-acting the compiler yourself on paper, essentially.

I think that’s true for just about any programming languages, though the program you’re “compiling” is a human understanding of what you’re trying to accomplish. Things like val bar = foo.let { it.widget?.frub() ?: FrubFactory::defaultFrub(it) } don’t come naturally to the human mind, you’re already working through the logic required before you start typing.

As for the x86 instruction count: you don’t need to know all of them. For instance, here’s a quick graph of all of the instructions in systemctl on my system:

https://popplesburger.hilciferous.nl/pictrs/image/a35a14ee-93fa-45c7-ae88-95119c39cd2c.png

With the top 15 or maybe to 25 of these instructions, you can probably write any program you can think of, and what’s missing will probably be easily found (just search for “multiply” or “divide”). You don’t need to know punpckldq to write a program.

luciferofastora ,

What language is your pseudocode example modeled after? It vaguely reminds me of some iOs App code I helped debug (Swift?) but I never really learned the language so much as eyeballed it with educated guesses, and even with the few things I double checked it has been a few years, so I have no clue what is or isn’t legal syntax anymore.

skullgiver ,
@skullgiver@popplesburger.hilciferous.nl avatar

That’s Kotlin. Mostly used for programming for the JVM, though it compiles to native code as well these days. Very interesting for cross platform app development, although I rarely do that these days.

I think Swift has a similar syntax, but it doesn’t do some of the less obvious Kotlin tricks as far as I’m aware.

luciferofastora ,

I’ve heard of Kotlin in the context of Android apps, but never actually used or learned it. I did one mobile app dev project with Java in Android Studio, but never had any formal classes on it either and just learned as I went (the result was shit, but we got a decent grade for being able to evaluate the difficulties and shortcomings and point out learnings).

CanadaPlus , (edited )

TIL. I had tried to understand it a bit, but felt lost pretty fast, and then eventually found out that’s because it’s huge. Is there a good intro to the basic instructions you’re aware of?

By “play act the compiler” I mean a fairly elaborate system of written notes that significantly exceeds the size of the actual program. Like, it’s no wonder they started thinking about building machine compilers at that stage.

skullgiver , (edited )
@skullgiver@popplesburger.hilciferous.nl avatar

I believe this guide can get you started pretty quickly to get the basics down. There are tons of guides online, but most of them will give you the basics (“this is how to find a prime number”) and then leave you on your own. Once you know how instructions, calling conventions, and system calls work, the rest of assembly programming is just reading documentation or Googling “how do I X in assembly”.

What can help is using websites like godbolt.org to write simple C programs and looking at the compiled output. Look up instructions you don’t recognize and make sure you don’t enable optimizations, unless you want to deal with atrocities like VGF2P8AFFINEINVQB.

If you don’t mind getting started with old assembly, there are also more comprehensive guides for MS-DOS and old Windows that mostly involve 16 bit and 32 bit programs programming. 64 bit programming is different (uses more registers to pass variables, floating point support is guaranteed, etc.) but there aren’t as many good books on the topic anymore now that it’s become a niche.

I think there are quite a few guides out there for ARM these days, if you have something like a Raspberry Pi or an emulator you can also learn ARM assembly (which has fewer supported weird instructions, but also a tonne of weird stuff).

If you want to go deep, you can also check Ben Eater’s youtube channel where he shows step by step how an 8 bit computer on a breadboard works, how instructions relate to memory, and all that. With some intuition from that, learning amd64 assembly may be a lot easier than going from normal programming languages to assembly.

Edit: to get into understanding assembly programming, [Human Resource Machine[(store.steampowered.com/…/Human_Resource_Machine/) will explain the concepts of assembly programming without ever overtly explaining the concepts. Plus, it’s a fun puzzle game.

CanadaPlus ,

Thank you!

luciferofastora ,

Having toyed with video game reverse engineering, I definitely feel like I ought to learn a bit more. I understand mov, pointers and registers, and I think there was some inc and add in the code I read to try to figure out base pointers and pointer paths (using Cheat Engine), but I think knowing some more would serve me well there.

skullgiver ,
@skullgiver@popplesburger.hilciferous.nl avatar

Modern decompilers like the one packaged with Ghidra helps a lot for intuiting how instructions work. Unfortunately, a lot of video game code is obfuscated, so you’re probably more likely to run into weird instructions, but OK the other hand you’ll learn what they do faster than when you rarely encounter them.

If you want to write amd64 code, you can get away with mastering just one instruction, and that’s the kind of tomfoolery that obfuscated programs will try to use to make your life harder.

leo85811nardo ,

From my understanding, one of the actual use case of assembly is for cyber security engineers to dump assembly instructions from a compiled program, so they can check for any potential vulnerability. I’ve also seen assembly included in an embedded codebase (the overall project is in C), which I assume is for more optimized performance and deterministic behavior

AFKBRBChocolate ,

I had an assembly class in college. I didn’t love of at all. Got my first job after graduating and it was writing space shuttle engine control software, which was in assembly. I was kind of surprised at how fast it became natural after dealing with it full time. Still, it felt luxurious when we upgraded the controller and could do the software in C.

leisesprecher ,

“oh no, I had to do literal rocket science”

r00ty Admin ,
r00ty avatar

I used to write z80 asm without an assembler back when I was a LOT younger. The ZX spectrum manual I had, had the full instruction list with the byte values.

I think it was oddly easier than some higher level languages for some tasks.

But, making changes was an utter nightmare.

TunaCowboy ,

Syscalls are sitting right there, and you can always just link libc…

jaybone ,

Assembly used to be a required course for CS undergrads in the 90s. Is that no longer the case?

Also we had to take something called Computer Architecture, which was like an EE class designing circuits with gates and shit.

CanadaPlus ,

Which target did you use? Having to learn even a fraction of modern x86 would be ridiculous, but SPARC or something could be good to know, just to reduce the “magic box” effect.

jaybone ,

This was a long time ago. I’m pretty sure it was 8086.

0x0 ,

I learned MIPS as an undergrad. Pretty neat little RISC architecture.

trolololol ,

I learned mips as graduate. In undergrad had to build with logic gates for things like 2 digit decimal counter and my architecture classes were diagram blocks for a simple CPU. But by that time we knew how to do moderate complexity circuits in VHDL simulation, and we had to make a simple VHDL circuit run for real in FPGA.

LodeMike ,

Its still a thing

czardestructo ,
@czardestructo@lemmy.world avatar

Required course work for electrical engineers in the early 2000s.

trolololol ,

I had to learn assembly but was one topic of many we handled in architecture. Like one question of one exam. That was one of the toughest professors we had, class was about 2001

SomGye ,

I still had to do that in the late 2010s in college

Cethin ,

I think the university I went to phased out the EE requirements the year after me. Honestly, I think it should be required. Understanding how the computer “thinks” is such an important skill.

luciferofastora ,

I attended two different Bachelor’s courses, one with a very technical (2016-2018) and one with a more high level focus (2018-2023). The first did have a class where we learned how to go from logic gates to a full ALU as well as some actual EE classes, but I didn’t go far enough or memorise the list of classes to remember whether Assembly would have become a thing. We learned programming with first Processing, then C and C++.

The second had C as an elective course, and that was as technical and low-level as it ever got.

darklamer ,
@darklamer@lemmy.dbzer0.com avatar

It’s now been 18 years since the last time an employer paid me to write assembly, but it’s only been a year or so since the last time I had to read assembly at work (in order to verify what the compiler really was doing).

NauticalNoodle ,

I’ve been studying Arm Aarch32 lately. I have a software development academic background but I have always been interested in Architecture.

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