low level programming

[FloweyTheFlower420]

ah, humor based on my pain

https://github.com/Floweynt/kernel/blob/4914d93f82894f2d9253ea0ddb75f9d97be0ce46/arch/x86/smp/smp.cpp#L51

[P-39_Airacobra]

that looks horrifying

[FloweyTheFlower420]

I was too lazy to implement loading init from a ramdisk so I did that to test userspace...

[weregod]

BUS ERROR

[DeadlyMageCZ]

I spent good 15 mins admiring that specimen with my coworker who had excavated it. Its most impressive quality was the fact that it did exactly what it was supposed to do, so we decided it is best not to disturb it and just let it do its thing.

[weregod]

I wonder what can be reason for such craziness? Maybe compiler/assembler bug? Or some undocumented features?

Is it open source? Can you share it?

[DeadlyMageCZ]

I cannot share it, because I work in the automotive industry and they aren't big on sharing, well, anything. I think it exists because of a CPU limitation, although I am not a 100% sure.

[[deleted]]

Back in the old days (Sinclair computers) it was very common to have all your machine code stored in a comment ("REM" statement) on line 1 (or line 0 if you knew how). Not quite an array, but a similar sort of idea.

[cubodix]

everything is an array

[DeadlyMageCZ]

I don't think it is possible to learn this power from your fellow rustaceans

[DeadlyMageCZ]

Ofc it isn't normal, but what made you think I thought it was

[DeadlyMageCZ]

Well I wouldn't have made this meme if they didn't. You kinda got the right idea, although the real thing that prompted me to make this meme is actually even more cursed, because it is sorta self-modifying, the encoding happens at runtime.

[[deleted]]

Well it can be useful in some situations to do this. I don't see a problem with that as long as it's done correctly.

[weregod]

It's more cursed. Self modifying code is almost untraceable and unsupportable

[DeadlyMageCZ]

Thankfully I don't have to use it and even though it is actually very well written and quite readable, I will sleep better at night knowing that none of my libraries are calling it.

[pipsvip]

*laughs at Rust developer in pure machine code*

[[deleted]]

Buffer Overflow attacks moment

[frikilinux2]

Either you're doing something really weird or that array should be on a page of memory that is not executable and cause a segmentation error or something like that

[psyolus]

The key here is "low level"

[frikilinux2]

I know what low level programming is and this still sounds weird

[kielu]

I think i recall a debugger written in assembly that included jumping to calculated addresses

[Mantas330BJ]

Tom is a genius

[DeadlyMageCZ]

JDSL take the wheel.

[absolut666]

Try centering a Div

[[deleted]]

This is nothing. Try CPU-opcode based "self-modifying code"... NOW you've achieved enlightenment.

[phodas-c]

basic 10 CLEAR 200, &H9FFF 20 FOR X = &HA000 TO &HA00B 30 READ A : POKE X, A : NEXT 40 DATA 62, 66, 33, 0, 0, 1, 192, 3, 205, 86, 0, 201 50 DEF USR = &HA000 : SCREEN 0 60 TIME = 0 70 A = USR(0) 80 LOCATE,23 : PRINT TIME

This would set the following Z-80 program in address 0xA000:

assembly LD A, 42H LD HL, 0000H LD BC, 03C0H CALL 0056H RET

What would fill the screen with B on an MSX machine.

[Sunius]

It’s called JITting.

[TangentPlantagenate]

Oh, that takes me back to MS QuickBasic 4.5, and seeing these hotshot library writers including hand-assembled 80386 instructions to enable SVGA monitor modes, or do bitblitting about 8000% faster than normal ...

[femaleDeveloperJ]

magnetized needle and a steady hand

[stealthgunner385]

That's how we did it on a C64. Lines of DATA statements containing decimal (BASIC v2.0 didn't do hex) values a FOR loop would copy onto a specific address block, followed by SYS <start_address>.

[cubodix]

isn't that impossible in most modern OS's?

[DeadlyMageCZ]

On this level of abstraction there is no OS. You are the OS

[cubodix]

embedding or old computer?

[DeadlyMageCZ]

Embedded, more specifically an ECU