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Things I learned while writing an x86 emulator (2023)

timdbg.com

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Re: Things I learned while writing an x86 emulator (2023)

#12

Post by actionfromafar »

sdsd wrote: post #4

What a cool person. I really enjoy writing assembly, it feels so simple and I really enjoy the vertical aesthetic quality. The closest I've ever come to something like OP (which is to say, not close at all) was when I was trying to help my JS friend understand the stack, and we ended up writing a mini vm with its own little ISA: https://gist.github.com/darighost/2d880fe27510e0c90f75680bfe... This could have gone much…

You should leverage that into your friend teaching you JS, maybe.

Re: Things I learned while writing an x86 emulator (2023)

#16

Post by waynecochran »

Intel architecture is loaded with historical artifacts. The switch in how segment registers were used as you went from real mode to protected mode was an incredible hardware hack to keep older software working. I blame Intel for why so many folks avoid assembly language. I programmed in assembly for years using TI's 84010 graphics chips and the design was gorgeous -- simple RISC instruction set, flat address space, and bit addressable! If during the earlier decades folks were programming using chips with more elegant designs, far more folks would be programming in assembly language (or at least would know how to).

Re: Things I learned while writing an x86 emulator (2023)

#17

Post by x0x0 »

trealira wrote: post #9
dmitrygr wrote: post #5

I've written fast emulators for a dozen non-toy architectures and a few JIT translators for a few as well. x86 still gives me PTSD. I have never seen a messier architecture. There is history, and a reason for it, but still ... damn

Studying the x86 architecture is kind of like studying languages with lots of irregularities and vestigial bits, and with competing grammatical paradigms, e.g. French. Other architectures, like RISC-V and ARMv8, are much more consistent.

I think English may be a better example; we just stapled chunks of vulgar latin to an inconsistently simplified proto-germanic and then borrowed words from every language we met along the way. Add in 44 sounds serialized to the page with 26 letters and tada!

Re: Things I learned while writing an x86 emulator (2023)

#18

Post by CoastalCoder »

aengelke wrote: post #10

Bonus quirk: there's BSF/BSR, for which the Intel SDM states that on zero input, the destination has an undefined value. (AMD documents that the destination is not modified in that case.) And then there's glibc, which happily uses the undocumented fact that the destination is also unmodified on Intel [1]. It took me quite some time to track down the issue in my binary translator. (There's also TZCNT/LZCNT, which is B…

Can you imagine having to make all this logic work faithfully, let alone fast, in silicon?

X86 used to be Intel's moat, but what a nightmarish burden to carry.

Re: Things I learned while writing an x86 emulator (2023)

#19

Post by hajile »

waynecochran wrote: post #16

Intel architecture is loaded with historical artifacts. The switch in how segment registers were used as you went from real mode to protected mode was an incredible hardware hack to keep older software working. I blame Intel for why so many folks avoid assembly language. I programmed in assembly for years using TI's 84010 graphics chips and the design was gorgeous -- simple RISC instruction set, flat address space, a…

> I blame Intel for why so many folks avoid assembly language.

x86 (the worst assembly of any of the top 50 most popular ISAs by a massive margin) and tricky MIPS branch delay slots trivia questions at university have done more to turn off programmers from learning assembly than anything else and it's not even close.

This is one reason I'm hoping that RISC-V kills off x86. It actually has a chance of once again allowing your average programmer to learn useful assembly.

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