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Linux Getting Extensive x86 Assembly Code Refresh
jones_supa writes: A massive x86 assembly code spring cleaning has been done in a pull request that is to end up in Linux 4.1. The developers have tried testing the code on many different x86 boxes, but there's risk of regression when exposing the code to many more systems in the days and weeks ahead. That being said, the list of improvements is excellent. There are over 100 separate cleanups, restructuring changes, speedups and fixes in the x86 system call, IRQ, trap and other entry code, part of a heroic effort to deobfuscate a decade old spaghetti assembly code and its C code dependencies.
Technical Debt haunts you.
The only way to truly understand C code is to read the disassembly. Otherwise you are only assuming what the compiler is emitting.
if they want to audit those stale old things for correctness and performance, and make them more readable for future generations, and
do the testing and review to make sure they haven't fucked them up
then good for them. i mean really good for them.
any code - especially the kernel - isn't a concrete artifact, its a process. an organism.
heathy organisms eliminate their wastes
and a 2% performance bump in system call overhead isn't anything to sneeze at
Who can sight read assembly anymore?
Everybody who is interested in "How Things Work" can read assemblly code. Those who depend on hopes and prayers do not.
Time is what keeps everything from happening all at once.
It's not a major refresh, only a modest one, and it doesn't really fix the readability issues (which would require a complete rewrite). Linux assembly is a mostly unreadable, badly formatted, macro-happy mess. The assembly in the BSDs is much more elegant and minimalistic.
-Matt
I do enjoy how we tech people less-than-quietly display our scorn of all the varying fields in IT that aren't our own. Because, hah, stupid Javascript developer, couldn't explain northbridge from south! Or what DMA is! He probably doesn't know a single assembly instruction! Clearly an inferior being.
Javascript guy meanwhile regards the C guy as a primitive, bearded man from the hills who labors all day on some stupid library that is ten layers of stack between that mortar and pestle and the awesome browser-art he's creating.
Systems administrators wish everyone would run off and die because they are all irritating, stupid whiners.
DBAs are just smug because nobody else understands their schemas and, hey, this is where it all happens.
Networking would rather be back below the hold, No, the network isn't broken, your app is buggy or the stupid website you're trying to load is just slow..
Help desk guys meanwhile consider themselves the cocks of the walk because, generally, their camaraderie and opportunity to interact with more regular people means their souls haven't been totally crushed.
I'm sure you're right, though they have something to do with micokernels. There was Linus interview from a few years back explaining his preference for the monolithic approach, and he explained that modules were introduced to give most of the benefits of the microkernel, without the drawbacks.
I'd have to see that interview to believe that's exactly what he said. In this essay by him, he says
but doesn't at all tie that to microkernels.
Loadable kernel modules in UN*Xes date back at least to SunOS 4.1.3 and AIX 3.0 in the early 1990's. I'm not sure they were introduced to compete with microkernels.
I don't really know why.
Users will say "But it works, we don't want to change waaagh scary" while simultaneously reporting 237 bugs all of which are OMG critical. Management will assume that it's cheaper, because existing stuff is already there so it's wasteful not to use it.
Now it's true that once a load of crufty business rules have built up with 17 levels of nested conditionals it can be risky to try and replicate it for fear of missing some obscure case that's bound to occur at an inconvenient time for a key customer. There's no documentation, of course. Or if there is it's the source code, six revisions behind, pasted into a word document with three screenshots taken as BMPs so the whole thing is 1.5G. This alone can make you say "sod it".
I can't find the correct phrase but maybe it's just a false analogy with physical things. Like reusing wood from an old shed to build a deck possibly is cheaper.
Confucius say, "Find worm in apple - bad. Find half a worm - worse."
You're operating on the mistaken assumption that code that works now will always work and never need to be modified. You can't leave anything but the simplest things alone forever, because changes to the context/world will eventually require changes to it. If it's spaghetti code, that's going to be causing future bugs that are going to be non-obvious and difficult to discover.
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I am "in Software" since ~25 years. I also hold a degree as a Software Engineer.
People who obsess about rewriting old code just because it's old tend to forget that in that old code are many bug fixes for edge cases found over the years. It was well documented and part of my education to know and understand that rewriting often caused those same bugs to surface again.
Best practice is to run both the old and new software in tandem for a while and verify the results. In reality no organization besides NASA will do that.
it's in my head