7 ms·

Show HN: Servasm – Literate web server in x86 assembler

117 points by zrkzrk 11y ago

mlitchard 11y ago
At first I was thinking "For the love of bog why?", but then I started reading, and couldn't stop reading.
deleted 11y ago
[deleted]
marktangotango 11y ago
If anyone finds this interesting, and would like to drill down into this type of low level code, I highly recomment "Programming from the Ground Up" by Jonathan Bartlett [1]. It is an excellent introduction to assembler, and programming in general. [1] http://freecomputerbooks.com/Programming-from-the-Ground-Up.html http://freecomputerbooks.com/Programming-from-the-Ground-Up....
- justwannasing 11y ago
  The non-spam link to download is here: http://download.savannah.gnu.org/releases/pgubook/ http://download.savannah.gnu.org/releases/pgubook/
Ellipsis753 11y ago
Interesting read and I like it. I'll have to read it more on my Desktop. I get a HTTPS error on my android phone however. You might be missing an intermediate certificate. (Just a heads up.)
- jaddison 11y ago
  As do I on my Android lollipop 5.1.
  - zrkzrk 11y ago
    Thanks, I will look into this. After running ssl test from ssl labs and I some alarming issues https://www.ssllabs.com/ssltest/analyze.html?d=zarkzork.com https://www.ssllabs.com/ssltest/analyze.html?d=zarkzork.com I should have done it earlier
    - jaddison 11y ago
      Surprisingly, I get this fairly often on my mobile. I'm not quite sure what's changed with the last version (or couple) of Android to trigger this. Over-secure, perhaps?
      - dmytrish 11y ago
        Android mobile browser requires the full signature chain of authorities who signed the site certificate[0]. It is done to avoid calls to CA servers and reduce network use on mobile devices. If a person does not concatenate authorities signatures to their site certificate, Firefox and mobile Chrome will alert, desktop Chrome and Safari won't. [0] https://en.wikipedia.org/wiki/OCSP_stapling https://en.wikipedia.org/wiki/OCSP_stapling
vezzy-fnord 11y ago
Annotations aside, this is actually more readable than a lot of C code I've seen.
- pmalynin 11y ago
  Thats funny because C is a one-to-one mapping over assembly. And frankly its not using any esoteric instructions such as "PUNPCKHQDQ" or "VFNMADD231PS"
  - TheLoneWolfling 11y ago
    What's wrong with "Unpack and interleave high-order quadwords from xmm1 and xmm2/m128 into xmm1." and "Multiply packed single-precision floating-point val-ues from ymm1 and ymm2/mem, negate the multi-plication result and add to ymm0 and put result in ymm0."? It's simple, right? (This is sarcasm, by the way.) Although I will point out that C has its esoterics also.
    - vardump 11y ago
      Both "esoteric" examples were just picked from a larger set of data packing and FMA (fused multiply add) operations that high performance real life code needs and uses. Intel doesn't generally add instructions no one needs. Unfortunately, compilers aren't indeed very good at picking optimal instructions when it could take good advantage of instructions such as these. No wonder, though. Packing and unpacking are often needed in SIMD context. There are a lot of such instructions, including shuffles and permutes. Individually they may sound esoteric, but actually cover a nice number of real life data shuffling needs and are extremely fast. Fused-multiply-add instructions can double effective FLOPS.
      - TheLoneWolfling 11y ago
        I am well aware of the potential advantages of such operations. And the difficulties associated with trying to use them well and identify when they can be an advantage. However, just because something is useful does not preclude it from being esoteric. In particular, there are an astounding number of such miscellaneous and less-often-used instructions in x86 and extensions, and trying to remember which ones exist, and which ones have which limitations, is... a fair feat. Hence, esoteric. Understood only by a few with special knowledge or interest.
vmorgulis 11y ago
It is very interesting. I like the simplicity of the system calls. With DynASM (a subproject of LuaJIT), it is possible to target more platforms with this kind beauty. http://luajit.org/dynasm_features.html http://luajit.org/dynasm_features.html
elmar 11y ago
Simply beautiful and elegant, probably very fast and with a very small memory footprint.
dingdingdang 11y ago
Would love to see benchmark on this versus nginx for fun!
- jandrese 11y ago
  Other than needing to fork for every request, this should be really fast because it uses the efficient sendfile() mechanism in the kernel to handle returning the file and most importantly only implements a bare minimum of support for the protocol. nginx is almost certainly going to be slower because it has to worry about different types of requests, different protocols, IPv4 vs. V6 sockets, CGI, etc... It's easy to make something fast when you only implement a very small number of features.
  - chralieboy 11y ago
    nginx is highly configurable at compile time. You can strip out a considerable amount of functionality (modules, in nginx lingo) for performance.
  - filsmick 11y ago
    IIRC, Nginx can use sendfile too, it's just not there by default because the transfer happens entirely in kernel space and hence you cannot apply filters like gzip on the response (correct me if I'm wrong).
  - dingdingdang 11y ago
    Yes, that's what my sense is: it would, within its very limited domain, beat nginx and co. fairly easily.. its interesting because this sort of thing could be made to be modular and thus feature extendable without the overhead if done in a smart enough fashion - many webservices today are sufficiently specialized that they only use a fraction of the features that modern webservers include.
e12e 11y ago
Very nice. However, I wonder who started this trend of bundling "better commented code" with "literate programming" though? I appreciate the layout and hyperlinks etc - but this really is just a well-structured assembly program laid out in a way that it won't assemble until after it's been through a pre-processor (I'm talking about the program as presented with html/css etc). It's pretty far from "literate programming". I suppose one could argue that if you manage to simplify the structure of your program to the point that it reads like prose, one has a "literate program". But it's a strange use of the term. The core idea is to have the code be incidental to the commentary, so that, among other things, one would update the commentary whenever one change the program. Laying out the comments in a funny way doesn't quite do that. I first saw this with the "literate" re-write of coffee script, but perhaps it's older? Perhaps the difference between "old" literate programming, and this style ("prose programming"?) is similar to the difference between unit testing and TDD, or between TDD and BDD?
- jostylr 11y ago
  One functional feature that is missing is that of having blocks in different order. Jeremy Ashkenas argues that because of functions, we do not need that reordering. I disagree with that. I do think a large part of what makes literate programming powerful is that one can easily sculpt the order of the presentation. It elevates the code and comment to telling a story for humans. I think the code is not incidental, but is part of the aspect of the story, much like in a fictional story one has descriptive passages and dialog passages. If one updates the story, both may change or perhaps just one of them. My take on literate programming, using markdown: * minimal client at https://www.npmjs.com/package/litpro https://www.npmjs.com/package/litpro * core library and docs at https://github.com/jostylr/literate-programming-lib https://github.com/jostylr/literate-programming-lib
  - e12e 11y ago
    I agree that functions are not usually a good one-to-one fit for abstraction. If they were, we wouldn't need variables, loops, blocks etc. Now you could argue that we don't, we should just write code in lambda calculus -- but we don't do that. Especially for languages like assembler and C-like languages, it can be very nice to single out smaller sections of code. And while for eg: C, or I suppose a macro assembler, one might be able to in-line a lot of such blocks -- having to stay at the "block-semantic"-level of the host language can make some things pretty hard to communicate to the human reader in a good way. Ruby might actually be a good candidate for "simple" literate programming, in the sense that one probably could, and perhaps sometimes should, program ruby much like smalltalk -- no method/function longer than five lines or so, except for the most exceptional circumstances. Even then, I think one would find patterns that would make sense to abstract out of the "function level", or "language level". At the other end of the spectrum is too much magic, just as with any meta-programming technique, such as proper macros. I had a most peculiar experience trying to write some (mostly procedural) java with noweb. It was typical intro programming stuff, basically some very simple data structures/algorithms. It was a very nice fit for literate programming, but not such a good fit for java -- while the literate program read nicely, and was well structured, the mangled java code was unwieldy -- it turned out I'd ended up generating a java program that did what I wanted. Now, that's not really a problem, we generate assembly programs that are unwieldy all the time -- but the point is it took some discipline and thought to write a literate program that was also readable in it's tangled form. Only an issue if people are expected to read/modify it in that state, obviously. And they are, as they'll have to debug it at some point ;-) > I think the code is not incidental That was a bit tongue-in-cheek -- I meant more in the sense that comments are incidental to code in most programming languages. > https://github.com/jostylr/literate-programming-lib https://github.com/jostylr/literate-programming-lib Very nice, thank you for sharing.
pointernil 11y ago
That's really fascinating and interesting and educating. Now every other http server implementation should need to explain every byte it is larger and every ms it is slower it terms of "why?" and "what for?" and "who gains from this?" ;) I don't know, for longer already I don't buy this tales about "it needs to be this large because..." ... mostly legacy, abstractions and ease of code maintenance etc. This took us all into the world in which the very smallest app on the phone reacting to a click with a "beep" takes how much memory? And the software development craft accepts unbelievable inefficiencies. Memory, Cpu manufactures for long time added to this fires by essentially mis-nurturing devs by optimizing in the background and by creating an environment of limitless virtual resources. I like how "battery-life" enforces, brings back some old ideas on efficiency and software craftsmanship. Humanity starts to deal with limits of its planet, its own limits and maybe this kind of thinking will bring back some level of limits into the virtual realms as well? I think we would gain from it.
- thoughtpolice 11y ago
  Are you being serious, or just trying to sound super philosophical about why "less is more"? I assume it's the latter, because it shouldn't take very much thought to see why HTTP servers are fairly complex pieces of software, given the purpose they serve - a class of software that is ruthlessly optimized in today's world - nor should it take very much thought to see this HTTP server is actually ridiculously inefficient compared to any modern one. You know, wasting all those precious CPU cycles you opine so much about? (Now, if you want to talk about the actual efficacy of HTTP vs other stateless protocols, that's a different story... But I doubt we're going to go there in a thread about an assembly HTTP server where people are ooh'ing over the achivement. Not that it isn't cool, TBQF.) Programmers at large really need to stop being pretend philosophers clutching at straws about "why things are so darn bad today!!!" (among other psuedo philosophical positions). They're mostly terrible at it, and it's almost always just so damn hamfisted and full of itself.
  - dang 11y ago
    Please be a little more charitable when commenting on HN. There is a long (albeit minority) tradition of thinking this way in computing, one that values small, intelligible systems as the best way for humans to work with computers. An example of this philosophy surfaced here recently (https://news.ycombinator.com/item?id=9689800 https://news.ycombinator.com/item?id=9689800) and there are countless others. HN itself has a rich history with this model. It was created by a practitioner of it, is written in a language inspired by it, and the smallness and intelligibility of the code are always on our minds when we work on it. We need more projects like this. They are deeply satisfying systems to build and work with, because they're human-scale in the way that behemoth software is not.

117 points by zrkzrk 11y ago

mlitchard 11y ago

At first I was thinking "For the love of bog why?", but then I started reading, and couldn't stop reading.

deleted 11y ago

[deleted]

marktangotango 11y ago

If anyone finds this interesting, and would like to drill down into this type of low level code, I highly recomment "Programming from the Ground Up" by Jonathan Bartlett [1]. It is an excellent introduction to assembler, and programming in general. [1] http://freecomputerbooks.com/Programming-from-the-Ground-Up.html http://freecomputerbooks.com/Programming-from-the-Ground-Up....

justwannasing 11y ago
The non-spam link to download is here: http://download.savannah.gnu.org/releases/pgubook/ http://download.savannah.gnu.org/releases/pgubook/

Ellipsis753 11y ago

Interesting read and I like it. I'll have to read it more on my Desktop. I get a HTTPS error on my android phone however. You might be missing an intermediate certificate. (Just a heads up.)

jaddison 11y ago
As do I on my Android lollipop 5.1.
- zrkzrk 11y ago
  Thanks, I will look into this. After running ssl test from ssl labs and I some alarming issues https://www.ssllabs.com/ssltest/analyze.html?d=zarkzork.com https://www.ssllabs.com/ssltest/analyze.html?d=zarkzork.com I should have done it earlier
  - jaddison 11y ago
    Surprisingly, I get this fairly often on my mobile. I'm not quite sure what's changed with the last version (or couple) of Android to trigger this. Over-secure, perhaps?
    - dmytrish 11y ago
      Android mobile browser requires the full signature chain of authorities who signed the site certificate[0]. It is done to avoid calls to CA servers and reduce network use on mobile devices. If a person does not concatenate authorities signatures to their site certificate, Firefox and mobile Chrome will alert, desktop Chrome and Safari won't. [0] https://en.wikipedia.org/wiki/OCSP_stapling https://en.wikipedia.org/wiki/OCSP_stapling

vezzy-fnord 11y ago

Annotations aside, this is actually more readable than a lot of C code I've seen.

pmalynin 11y ago
Thats funny because C is a one-to-one mapping over assembly. And frankly its not using any esoteric instructions such as "PUNPCKHQDQ" or "VFNMADD231PS"
- TheLoneWolfling 11y ago
  What's wrong with "Unpack and interleave high-order quadwords from xmm1 and xmm2/m128 into xmm1." and "Multiply packed single-precision floating-point val-ues from ymm1 and ymm2/mem, negate the multi-plication result and add to ymm0 and put result in ymm0."? It's simple, right? (This is sarcasm, by the way.) Although I will point out that C has its esoterics also.
  - vardump 11y ago
    Both "esoteric" examples were just picked from a larger set of data packing and FMA (fused multiply add) operations that high performance real life code needs and uses. Intel doesn't generally add instructions no one needs. Unfortunately, compilers aren't indeed very good at picking optimal instructions when it could take good advantage of instructions such as these. No wonder, though. Packing and unpacking are often needed in SIMD context. There are a lot of such instructions, including shuffles and permutes. Individually they may sound esoteric, but actually cover a nice number of real life data shuffling needs and are extremely fast. Fused-multiply-add instructions can double effective FLOPS.
    - TheLoneWolfling 11y ago
      I am well aware of the potential advantages of such operations. And the difficulties associated with trying to use them well and identify when they can be an advantage. However, just because something is useful does not preclude it from being esoteric. In particular, there are an astounding number of such miscellaneous and less-often-used instructions in x86 and extensions, and trying to remember which ones exist, and which ones have which limitations, is... a fair feat. Hence, esoteric. Understood only by a few with special knowledge or interest.

vmorgulis 11y ago

It is very interesting. I like the simplicity of the system calls. With DynASM (a subproject of LuaJIT), it is possible to target more platforms with this kind beauty. http://luajit.org/dynasm_features.html http://luajit.org/dynasm_features.html

elmar 11y ago

Simply beautiful and elegant, probably very fast and with a very small memory footprint.

dingdingdang 11y ago

Would love to see benchmark on this versus nginx for fun!

jandrese 11y ago
Other than needing to fork for every request, this should be really fast because it uses the efficient sendfile() mechanism in the kernel to handle returning the file and most importantly only implements a bare minimum of support for the protocol. nginx is almost certainly going to be slower because it has to worry about different types of requests, different protocols, IPv4 vs. V6 sockets, CGI, etc... It's easy to make something fast when you only implement a very small number of features.
- chralieboy 11y ago
  nginx is highly configurable at compile time. You can strip out a considerable amount of functionality (modules, in nginx lingo) for performance.
- filsmick 11y ago
  IIRC, Nginx can use sendfile too, it's just not there by default because the transfer happens entirely in kernel space and hence you cannot apply filters like gzip on the response (correct me if I'm wrong).
- dingdingdang 11y ago
  Yes, that's what my sense is: it would, within its very limited domain, beat nginx and co. fairly easily.. its interesting because this sort of thing could be made to be modular and thus feature extendable without the overhead if done in a smart enough fashion - many webservices today are sufficiently specialized that they only use a fraction of the features that modern webservers include.

e12e 11y ago

Very nice. However, I wonder who started this trend of bundling "better commented code" with "literate programming" though? I appreciate the layout and hyperlinks etc - but this really is just a well-structured assembly program laid out in a way that it won't assemble until after it's been through a pre-processor (I'm talking about the program as presented with html/css etc). It's pretty far from "literate programming". I suppose one could argue that if you manage to simplify the structure of your program to the point that it reads like prose, one has a "literate program". But it's a strange use of the term. The core idea is to have the code be incidental to the commentary, so that, among other things, one would update the commentary whenever one change the program. Laying out the comments in a funny way doesn't quite do that. I first saw this with the "literate" re-write of coffee script, but perhaps it's older? Perhaps the difference between "old" literate programming, and this style ("prose programming"?) is similar to the difference between unit testing and TDD, or between TDD and BDD?

jostylr 11y ago
One functional feature that is missing is that of having blocks in different order. Jeremy Ashkenas argues that because of functions, we do not need that reordering. I disagree with that. I do think a large part of what makes literate programming powerful is that one can easily sculpt the order of the presentation. It elevates the code and comment to telling a story for humans. I think the code is not incidental, but is part of the aspect of the story, much like in a fictional story one has descriptive passages and dialog passages. If one updates the story, both may change or perhaps just one of them. My take on literate programming, using markdown: * minimal client at https://www.npmjs.com/package/litpro https://www.npmjs.com/package/litpro * core library and docs at https://github.com/jostylr/literate-programming-lib https://github.com/jostylr/literate-programming-lib
- e12e 11y ago
  I agree that functions are not usually a good one-to-one fit for abstraction. If they were, we wouldn't need variables, loops, blocks etc. Now you could argue that we don't, we should just write code in lambda calculus -- but we don't do that. Especially for languages like assembler and C-like languages, it can be very nice to single out smaller sections of code. And while for eg: C, or I suppose a macro assembler, one might be able to in-line a lot of such blocks -- having to stay at the "block-semantic"-level of the host language can make some things pretty hard to communicate to the human reader in a good way. Ruby might actually be a good candidate for "simple" literate programming, in the sense that one probably could, and perhaps sometimes should, program ruby much like smalltalk -- no method/function longer than five lines or so, except for the most exceptional circumstances. Even then, I think one would find patterns that would make sense to abstract out of the "function level", or "language level". At the other end of the spectrum is too much magic, just as with any meta-programming technique, such as proper macros. I had a most peculiar experience trying to write some (mostly procedural) java with noweb. It was typical intro programming stuff, basically some very simple data structures/algorithms. It was a very nice fit for literate programming, but not such a good fit for java -- while the literate program read nicely, and was well structured, the mangled java code was unwieldy -- it turned out I'd ended up generating a java program that did what I wanted. Now, that's not really a problem, we generate assembly programs that are unwieldy all the time -- but the point is it took some discipline and thought to write a literate program that was also readable in it's tangled form. Only an issue if people are expected to read/modify it in that state, obviously. And they are, as they'll have to debug it at some point ;-) > I think the code is not incidental That was a bit tongue-in-cheek -- I meant more in the sense that comments are incidental to code in most programming languages. > https://github.com/jostylr/literate-programming-lib https://github.com/jostylr/literate-programming-lib Very nice, thank you for sharing.

pointernil 11y ago

That's really fascinating and interesting and educating. Now every other http server implementation should need to explain every byte it is larger and every ms it is slower it terms of "why?" and "what for?" and "who gains from this?" ;) I don't know, for longer already I don't buy this tales about "it needs to be this large because..." ... mostly legacy, abstractions and ease of code maintenance etc. This took us all into the world in which the very smallest app on the phone reacting to a click with a "beep" takes how much memory? And the software development craft accepts unbelievable inefficiencies. Memory, Cpu manufactures for long time added to this fires by essentially mis-nurturing devs by optimizing in the background and by creating an environment of limitless virtual resources. I like how "battery-life" enforces, brings back some old ideas on efficiency and software craftsmanship. Humanity starts to deal with limits of its planet, its own limits and maybe this kind of thinking will bring back some level of limits into the virtual realms as well? I think we would gain from it.

thoughtpolice 11y ago
Are you being serious, or just trying to sound super philosophical about why "less is more"? I assume it's the latter, because it shouldn't take very much thought to see why HTTP servers are fairly complex pieces of software, given the purpose they serve - a class of software that is ruthlessly optimized in today's world - nor should it take very much thought to see this HTTP server is actually ridiculously inefficient compared to any modern one. You know, wasting all those precious CPU cycles you opine so much about? (Now, if you want to talk about the actual efficacy of HTTP vs other stateless protocols, that's a different story... But I doubt we're going to go there in a thread about an assembly HTTP server where people are ooh'ing over the achivement. Not that it isn't cool, TBQF.) Programmers at large really need to stop being pretend philosophers clutching at straws about "why things are so darn bad today!!!" (among other psuedo philosophical positions). They're mostly terrible at it, and it's almost always just so damn hamfisted and full of itself.
- dang 11y ago
  Please be a little more charitable when commenting on HN. There is a long (albeit minority) tradition of thinking this way in computing, one that values small, intelligible systems as the best way for humans to work with computers. An example of this philosophy surfaced here recently (https://news.ycombinator.com/item?id=9689800 https://news.ycombinator.com/item?id=9689800) and there are countless others. HN itself has a rich history with this model. It was created by a practitioner of it, is written in a language inspired by it, and the smallness and intelligibility of the code are always on our minds when we work on it. We need more projects like this. They are deeply satisfying systems to build and work with, because they're human-scale in the way that behemoth software is not.