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• Debugging SQL Server Slowness: Same Database, Different Servers

  - by Craig Walker

  For a while now we've been having anecdotal slowness on our newly-minted (VMWare-based) SQL Server 2005 database servers. Recently the problem has come to a head and I've started looking for the root cause of the issue. Here's the weird part: on the stored procedure that I'm using as a performance test case, I get a 30x difference in the execution speed depending on which DB server I run it on. This is using the same database (mdf) and log (ldf) files, detached, copied, and reattached from the slow server to the fast one. This doesn't appear to be a (virtualized) hardware issue: he slow server has 4x the CPU capacity and 2x the memory as the fast one. As best as I can tell, the problem lies in the environment/configuration of the servers (either operating system or SQL Server installation). However, I've checked a bunch of variables (SQL Server config options, running services, disk fragmentation) and found nothing that has made a difference in testing. What things should I be looking at? What tools can I use to investigate why this is happening?

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• Ruby on Rails website hosting

  - by sfactor

  i want to start a website. it'll be a small community based website. i've learned a fair bit of ruby on rails and am planning to use it. however, i have never deployed a production website before. i've just practiced in my local computer. i wanted to know what are the things i need to deploy the website on the internet. what is the best place to get a domain name and web hosting, esp for ruby on rails sites. how are cloud based services like amazon EC2 etc different from a traditional web host. which is a better choice. what else might i need to do to deploy a website. also i may happen to have a fair bit of users in the future. so how to go about planning for scalability issues. how to sites like twitter, fmylife.com etc all go about these things.

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• Applications on the Web/Cloud the way to go? over Desktop apps?

  - by jiewmeng

  i am currently a mainly web developer, but is quite attracted to the performance and great integration with the OS (eg. Windows 7, Jump Lists, Taskbar Thumbnails, etc) something like WPF/C# can provide to the user, improving workflow and productivity. privacy and performance seems like a major downside of web/cloud apps compared to desktop apps. applications on the cloud/web work on the go, increased popularity of smartphones/netbooks majority of users may not benefit as much from increased performance of desktop apps, eg. internet surfing, word processing, probably benefit more from decreased startup times, lower costs and data on the cloud desktop applications increased performance benefits power users like 3D rendering, HD video/photo editing, gamers (i wonder if such processing maybe offset to cloud processing) integration with OS increases productivity (maybe such features can be adapted to a web version? maybe with a local desktop app to work with Web App API) more control over privacy (maybe fixed by encryption?) local data access (esp. large files) guaranteed and fast (YouTube HD fast enough most of the time) work not affected by intermittent/slow/availability internet connections (i know this is changing tho) what do you think?

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• Convert latitude and longitude into northings and eastings

  - by Rippo

  Hi I have the following UK postcode dy8 3xt and know that the latitude and longitude is:- 54.452772 -2.156082 I also know that the Eastings, Northings for the postcode is:- 389490 283880 However I am struggling to find the equation that converts lat/long to northings and Eastings, I would prefer to have the equation in both in jScript and c# (I am being greedy)! Can anyone help? EDIT Thanks for your help so far guys, I am starting to learn something here esp. the terminology... Some more info, if you click on this link you can see the results I am looking for. The postcode I entered projects to lat/lng using WG S84 and the grid ref projects to OSGB. So my question is how is this done? WHAT I LEARNT Thanks to all that answered, I finally got led to here which I can confirm works great

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• Windows mobile phone for business application - or design way out of scrolling problem

  - by Peter

  We have a business application written for Windows mobile. It has people doing inventories. The fastest way to do this is to keep one hand on the product being counted and the other on the phone. The five-way lets you hit enter to accept the current correct inventory (the norm) or to move one left to remove one. This is very fast. If I am two low, I have a quick glance at the phone- move my eyes back to count the next row - and with my right hand hit the five way "left left enter". Very fast. Our problem is that with I-Mate out of business, we cannot find a modern cell phone that has a decent size screen and a five way. Everyone is going to candy bar and flicks. That works great if it is two hands and you are looking at the phone, but not efficient for us. Other than the $1,500 ruggadized units, is there anybody who makes a business style Windows Mobile with a five way? If not, any ideas on how to design the phone to make it easier without a five way to quickly enter data like this?

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• How to scale a sprite image without losing color key information?

  - by Michael P

  Hello everyone, I'm currently developing a simple application that displays map and draws some markers on it. I'm developing for Windows Mobile, so I decided to use DirectDraw and Imaging interfaces to make the application fast and pretty. The map moves when user moves finger on the touchscreen, so the whole map moving/scrolling animation has to be fast, but it is not. On every map update I have to draw portion of the map, control buttons, and markers - buttons and markers are preloaded on DirectDraw surface as a mipmap. So the only thing I do is BitBlit from the mipmap to a back buffer, and from the back buffer to a primary surface (I can't use page flipping due to the windowed mode of my application). Previously I used premultiplied-alpha surface with 32 bit ARGB pixel format for images mipmap, everything was looking good, but drawing entire "scene" was horribly slow - i could forget about smooth map scrolling. Now I'm using mipmap with native (RGB565) pixel format and fuchsia (0xFF00FF) color key. Drawing is much better my mipmap surface is generated on program loading - images are loaded from files, scaled (with filtering) and drawn on mipmap. The problem is, that image scaling process blends pixel colors, and those pixels which are on the border of a sprite region are blended with surrounding fuchsia pixels resulting semi-fuchsia color that is not treated as color key. When I do blitting with color key option, sprites have small fuchsia-like borders, and it looks really bad. How to solve this problem? I can use alpha blitting, but it is too slow - even in ARGB 1555 format.

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• Simple Select Statement on MySQL Database Hanging

  - by AlishahNovin

  I have a very simple sql select statement on a very large table, that is non-normalized. (Not my design at all, I'm just trying to optimize while simultaneously trying to convince the owners of a redesign) Basically, the statement is like this: SELECT FirstName, LastName, FullName, State FROM Activity Where (FirstName=@name OR LastName=@name OR FullName=@name) AND State=@state; Now, FirstName, LastName, FullName and State are all indexed as BTrees, but without prefix - the whole column is indexed. State column is a 2 letter state code. What I'm finding is this: When @name = 'John Smith', and @state = '%' the search is really fast and yields results immediately. When @name = 'John Smith', and @state = 'FL' the search takes 5 minutes (and usually this means the web service times out...) When I remove the FirstName and LastName comparisons, and only use the FullName and State, both cases above work very quickly. When I replace FirstName, LastName, FullName, and State searches, but use LIKE for each search, it works fast for @name='John Smith%' and @state='%', but slow for @name='John Smith%' and @state='FL' When I search against 'John Sm%' and @state='FL' the search finds results immediately When I search against 'John Smi%' and @state='FL' the search takes 5 minutes. Now, just to reiterate - the table is not normalized. The John Smith appears many many times, as do many other users, because there is no reference to some form of users/people table. I'm not sure how many times a single user may appear, but the table itself has 90 Million records. Again, not my design... What I'm wondering is - though there are many many problems with this design, what is causing this specific problem. My guess is that the index trees are just too large that it just takes a very long time traversing the them. (FirstName, LastName, FullName) Anyway, I appreciate anyone's help with this. Like I said, I'm working on convincing them of a redesign, but in the meantime, if I someone could help me figure out what the exact problem is, that'd be fantastic.

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• Perl XML SAX parser emulating XML::Simple record for record

  - by DVK

  Short Q summary: I am looking a fast XML parser (most likely a wrapper around some standard SAX parser) which will produce per-record data structure 100% identical to those produced by XML::Simple. Details: We have a large code infrastructure which depends on processing records one-by-one and expects the record to be a data structure in a format produced by XML::Simple since it always used XML::Simple since early Jurassic era. An example simple XML is: <root> <rec><f1>v1</f1><f2>v2</f2></rec> <rec><f1>v1b</f1><f2>v2b</f2></rec> <rec><f1>v1c</f1><f2>v2c</f2></rec> </root> And example rough code is: sub process_record { my ($obj, $record_hash) = @_; # do_stuff } my $records = XML::Simple->XMLin(@args)->{root}; foreach my $record (@$records) { $obj->process_record($record) }; As everyone knows XML::Simple is, well, simple. And more importantly, it is very slow and a memory hog - due to being a DOM parser and needing to build/store 100% of data in memory. So, it's not the best tool for parsing an XML file consisting of large amount of small records record-by-record. However, re-writing the entire code (which consist of large amount of "process_record"-like methods) to work with standard SAX parser seems like an big task not worth the resources, even at the cost of living with XML::Simple. What I'm looking for is an existing module which will probably be based on a SAX parser (or anything fast with small memory footprint) which can be used to produce $record hashrefs one by one based on the XML pictured above that can be passed to $obj->process_record($record) and be 100% identical to what XML::Simple's hashrefs would have been.

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• Mutex names - best practice?

  - by Argalatyr

  Related to this question, what is the best practice for naming a mutex? I realize this may vary with OS and even with version (esp for Windows), so please specify platform in answering. My interest is in Win XP and Vista. EDIT: I am motivated by curiousity, because in Rob Kennedy's comment under his (excellent) Answer to the above-linked Question, he implied that the choice of mutex name is non-trivial and should be the subject of a separate question. EDIT2: The referenced question's goal was to ensure only a single instance of an app is running.

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• Sharing large objects between ruby processes without a performance hit

  - by Gdeglin

  I have a Ruby hash that reaches approximately 10 megabytes if written to a file using Marshal.dump. After gzip compression it is approximately 500 kilobytes. Iterating through and altering this hash is very fast in ruby (fractions of a millisecond). Even copying it is extremely fast. The problem is that I need to share the data in this hash between Ruby on Rails processes. In order to do this using the Rails cache (file_store or memcached) I need to Marshal.dump the file first, however this incurs a 1000 millisecond delay when serializing the file and a 400 millisecond delay when serializing it. Ideally I would want to be able to save and load this hash from each process in under 100 milliseconds. One idea is to spawn a new Ruby process to hold this hash that provides an API to the other processes to modify or process the data within it, but I want to avoid doing this unless I'm certain that there are no other ways to share this object quickly. Is there a way I can more directly share this hash between processes without needing to serialize or deserialize it? Here is the code I'm using to generate a hash similar to the one I'm working with: @a = [] 0.upto(500) do |r| @a[r] = [] 0.upto(10_000) do |c| if rand(10) == 0 @a[r][c] = 1 # 10% chance of being 1 else @a[r][c] = 0 end end end @c = Marshal.dump(@a) # 1000 milliseconds Marshal.load(@c) # 400 milliseconds

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• Force creation of query execution plan

  - by Marc

  I have the following situation: .net 3.5 WinForm client app accessing SQL Server 2008 Some queries returning relatively big amount of data are used quite often by a form Users are using local SQL Express and restarting their machines at least daily Other users are working remotely over slow network connections The problem is that after a restart, the first time users open this form the queries are extremely slow and take more or less 15s on a fast machine to execute. Afterwards the same queries take only 3s. Of course this comes from the fact that no data is cached and must be loaded from disk first. My question: Would it be possible to force the loading of the required data in advance into SQL Server cache? Note My first idea was to execute the queries in a background worker when the application starts, so that when the user starts the form the queries will already be cached and execute fast directly. I however don't want to load the result of the queries over to the client as some users are working remotely or have otherwise slow networks. So I thought just executing the queries from a stored procedure and putting the results into temporary tables so that nothing would be returned. Turned out that some of the result sets are using dynamic columns so I couldn't create the corresponding temp tables and thus this isn't a solution. Do you happen to have any other idea?

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• ARMv6 FIQ, acknowledge interrupt

  - by fastmonkeywheels

  I'm working with an i.mx35 armv6 core processor. I have Interrupt 62 configured as a FIQ with my handler installed and being called. My handler at the moment just toggles an output pin so I can test latency with a scope. With the code below, once I trigger the FIQ it continues forever as fast as it can, apparently not being acknowledged. I'm triggering the FIQ by means of the Interrupt Force Register so I'm assured that the source isn't triggering it this fast. If I disable Interrupt 62 in the AVIC in my FIQ routine the interrupt only triggers once. I have read the sections on the VIC Port in the ARM1136JF-S and ARM1136J-S Technical Reference Manual and it covers proper exit procedure. I'm only having one FIQ handler so I have no need to branch. The line that I don't understand is: STR R0, [R8,#AckFinished] I'm not sure what AckFinished is supposed to be or what this command is supposed to do. My FIQ handler is below: ldr r9, IOMUX_ADDR12 ldr r8, [r9] orr r8, #0x08 @ top LED str r8,[r9] @turn on LED bic r8, #0x08 @ top LED str r8,[r9] @turn off LED subs pc, r14, #4 IOMUX_ADDR12: .word 0xFC2A4000 @remapped IOMUX addr My handler returns just fine and normal system operation resumes if I disable it after the first go, otherwise it triggers constantly and the system appears to hang. Do you think my assumption is right that the core isn't acknowledging the AVIC or could there be another cause of this FIQ triggering?

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• dynamically horizontal scalable key value store

  - by Zubair

  Hi, Is there a key value store that will give me the following: Allow me to simply add and remove nodes and will redstribute the data automatically Allow me to remove nodes and still have 2 extra data nodes to provide redundancy Allow me to store text or images up to 1GB in size Can store small size data up to 100TB of data Fast (so will allow queries to be performed on top of it) Make all this transparent to the client Works on Ubuntu/FreeBSD or Mac Free or open source I basically want something I can use a "single", and not have to worry about having memcached, a db, and several storage components so yes, I do want a database "silver bullet" you could say. Thanks Zubair Answers so far: MogileFS on top of BackBlaze - As far as I can see this is just a filesystem, and after some research it only seems to be appropriate for large image files Tokyo Tyrant - Needs lightcloud. This doesn't auto scale as you add new nodes. I did look into this and it seems it is very fast for queries which fit onto a single node though Riak - This is one I am looking into myself, but I don't have any results yet Amazon S3 - Is anyone using this as their sole persistance layer in production? From what I have seen it seems to be used for storage of images as complex queries are too expensive @shaman suggested Cassandra - definitely one I am looking into So far it seems that there is no database or key value store that fulfills the criteria I mentioned, not even after offering a bounty of 100 points did the question get answered!

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• Handling conflicting priorities and expectations in project development

  - by jasonk

  There are any number of situations in the standard day where priority conflicts exist for projects. Management wants maximum productivity from employees. Marketing wants maximum salability and fast turnaround. Ownership wants maximum profit. Customers want usability and low cost. Regardless of the origin of the demands, time and money are always the limiting factor in business. Sometimes project elements have intrinsic or goodwill benefits for which there is not a hard, fast way to measure with monetary means (e.g. arguments for an attractive UI appeal vs. functional but plain). Other elements of software may have a method of providing “mental breaks” or motivating “cool factor” for developers that can get them back on track on other bigger, complex issues. While they may sidetrack the project short term they may have greater results long term through improved job satisfaction, etc. Continued training is a must, but working it in can setup back progress. What are your suggestions for setting priorities? How do you evaluate requests/demands on your projects? What are your suggestions for communicating and passing those on to your team in a way that they stay focused?

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• What algorithms are suitable for this simple machine learning problem?

  - by user213060

  I have a what I think is a simple machine learning question. Here is the basic problem: I am repeatedly given a new object and a list of descriptions about the object. For example: new_object: 'bob' new_object_descriptions: ['tall','old','funny']. I then have to use some kind of machine learning to find previously handled objects that had similar descriptions, for example, past_similar_objects: ['frank','steve','joe']. Next, I have an algorithm that can directly measure whether these objects are indeed similar to bob, for example, correct_objects: ['steve','joe']. The classifier is then given this feedback training of successful matches. Then this loop repeats with a new object. a Here's the pseudo-code: Classifier=new_classifier() while True: new_object,new_object_descriptions = get_new_object_and_descriptions() past_similar_objects = Classifier.classify(new_object,new_object_descriptions) correct_objects = calc_successful_matches(new_object,past_similar_objects) Classifier.train_successful_matches(object,correct_objects) But, there are some stipulations that may limit what classifier can be used: There will be millions of objects put into this classifier so classification and training needs to scale well to millions of object types and still be fast. I believe this disqualifies something like a spam classifier that is optimal for just two types: spam or not spam. (Update: I could probably narrow this to thousands of objects instead of millions, if that is a problem.) Again, I prefer speed when millions of objects are being classified, over accuracy. What are decent, fast machine learning algorithms for this purpose?

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• .post inside jQuery.validator.addMethod always returns false :(

  - by abdullah kahraman

  Hello! I am very new to jQuery and javascript programming. I have a program below that checks whether username is taken or not. For now, the PHP script always returns if(isset($_POST["username"]) )//&& isset($_POST["checking"])) { $xml="<register><message>Available</message></register>"; echo $xml; } Login function works, but username checking doesn't. Any ideas? Here is all of my code: $(document).ready(function() { jQuery.validator.addMethod("checkAvailability",function(value,element){ $.post( "login.php" , {username:"test", checking:"yes"}, function(xml){ if($("message", xml).text() == "Available") return true; else return false; }); },"Sorry, this user name is not available"); $("#loginForm").validate({ rules: { username: { required: true, minlength: 4, checkAvailability: true }, password:{ required: true, minlength: 5 } }, messages: { username:{ required: "You need to enter a username." , minlength: jQuery.format("Your username should be at least {0} characters long.") } }, highlight: function(element, errorClass) { $(element).fadeOut("fast",function() { $(element).fadeIn("slow"); }) }, success: function(x){ x.text("OK!") }, submitHandler: function(form){send()} }); function send(){ $("#message").hide("fast"); $.post( "login.php" , {username:$("#username").val(), password:$("#password").val()}, function(xml){ $("#message").html( $("message", xml).text() ); if($("message", xml).text() == "You are successfully logged in.") { $("#message").css({ "color": "green" }); $("#message").fadeIn("slow", function(){location.reload(true);}); } else { $("#message").css({ "color": "red" }); $("#message").fadeIn("slow"); } }); } $("#newUser").click(function(){ return false; }); });

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• Are there any radix/patricia/critbit trees for Python?

  - by Andrew Dalke

  I have about 10,000 words used as a set of inverted indices to about 500,000 documents. Both are normalized so the index is a mapping of integers (word id) to a set of integers (ids of documents which contain the word). My prototype uses Python's set as the obvious data type. When I do a search for a document I find the list of N search words and their corresponding N sets. I want to return the set of documents in the intersection of those N sets. Python's "intersect" method is implemented as a pairwise reduction. I think I can do better with a parallel search of sorted sets, so long as the library offers a fast way to get the next entry after i. I've been looking for something like that for some time. Years ago I wrote PyJudy but I no longer maintain it and I know how much work it would take to get it to a stage where I'm comfortable with it again. I would rather use someone else's well-tested code, and I would like one which supports fast serialization/deserialization. I can't find any, or at least not any with Python bindings. There is avltree which does what I want, but since even the pair-wise set merge take longer than I want, I suspect I want to have all my operations done in C/C++. Do you know of any radix/patricia/critbit tree libraries written as C/C++ extensions for Python? Failing that, what is the most appropriate library which I should wrap? The Judy Array site hasn't been updated in 6 years, with 1.0.5 released in May 2007. (Although it does build cleanly so perhaps It Just Works.)

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• How do I compile boost using __cdecl calling convention?

  - by Sorin Sbarnea

  I have a project compiled using __cdecl calling convention (msvc2010) and I compiled boost using the same compiler using the default settings. The project linked with boost but I at runtime I got an assert message like this: File: ...\boost\boost\program_options\detail\parsers.hpp Line: 79 Run-Time Check Failure #0 - The value of ESP was not properly saved across a function call. This is usually a result of calling a function declared with one calling convention with a function pointer declared with a different calling convention. There are the following questions: what calling convention does boost build with by default on Windows (msvc2010) how to I compile boost with __cdecl calling convention why boost wasn't able to prevent linking with code with different calling conventions? I understood that boost has really smart library auto-inclusion code.

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• JQuery - nested ul/li list, keep expanded after reload of page

  - by H4mm3rHead

  Hi, I have a nested ul/li list <ul> <li>first</li> <li>second <ul> <li>Third</li> </ul> </li> ... and so on I found this JQuery on the interweb to use as inspiration, but how to keep the one item i expanded open after the page has reloaded? <script type="text/javascript"> $(document).ready(function() { $('div#sideNav li li > ul').hide(); //hide all nested ul's $('div#sideNav li > ul li a[class=current]').parents('ul').show().prev('a').addClass('accordionExpanded'); //show the ul if it has a current link in it (current page/section should be shown expanded) $('div#sideNav li:has(ul)').addClass('accordion'); //so we can style plus/minus icons $('div#sideNav li:has(ul) > a').click(function() { $(this).toggleClass('accordionExpanded'); //for CSS bgimage, but only on first a (sub li>a's don't need the class) $(this).next('ul').slideToggle('fast'); $(this).parent().siblings('li').children('ul:visible').slideUp('fast') .parent('li').find('a').removeClass('accordionExpanded'); return true; }); }); </script>

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• Kernel panic when altering system_call in entry.S

  - by EpsilonVector

  I'm trying to implement a system call counter, and as a result I included an int value in task_struct, and a function that increments it in a separate file. This function is supposed to be called from system_call right before it actually calls the required sys_call (I have my reasons to call it before and not after). However, if I place it before the sys_call then after compiling and booting there's a kernel panic ("tried to kill init_idle"), and if I place it right after the sys_call, it works. What's the difference and how do I overcome this? Here's the relevant code ENTRY(system_call) pushl %eax # save orig_eax SAVE_ALL GET_CURRENT(%ebx) testb $0x02,tsk_ptrace(%ebx) # PT_TRACESYS jne tracesys cmpl $(NR_syscalls),%eax jae badsys call update_counter /*This causes a kernel panic*/ call *SYMBOL_NAME(sys_call_table)(,%eax,4) movl %eax,EAX(%esp) # save the return value

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• Credit card payment method

  - by Rudy

  Hi guys, I'm creating a online webshop using ASP .net and C#. The website is supposed to receive payment by master card, visa, paypal, and e-transfer. Any reference how can I do that, esp for master card and visa. Is it done via web service? Do i hv to use a payment gateway? Is it possible to connect directly to MC and visa? I totally have no clue on this. Thanks!

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• C++ Primer (Stanley Lipmann) or The C++ programming language (special edition)

  - by Kim

  I have a Computer Science degree (long2 time ago) .. I do know Java OOP but i am now trying to pick up C++. I do have C and of course data structure using C or pascal. I have started reading Bjarne Stroustrup book (The C++ Programming Language - Special Edition) but find it extremely difficult esp. some section which i don't have exposure such as Recursive Descent Parser (chapter 6). In terms of the language i don't foresee i have problem but i have problem as mentioned cos' those topic are usually covered in a Master Degree program such as construction of compiler. I just bought a book called C++ primer (Stanley Lipmann) which i heard it is a very good book for C++. Only setback is it's of course no match with the amount of information from the original C++ creator. Please advice. Thanks.

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• How do I store complex objects in javascript?

  - by Colen

  Hello, I need to be able to store objects in javascript, and access them very quickly. For example, I have a list of vehicles, defined like so: { "name": "Jim's Ford Focus", "color": "white", isDamaged: true, wheels: 4 } { "name": "Bob's Suzuki Swift", "color": "green", isDamaged: false, wheels: 4 } { "name": "Alex's Harley Davidson", "color": "black", isDamaged: false, wheels: 2 } There will potentially be hundreds of these vehicle entries, which might be accessed thousands of times. I need to be able to access them as fast as possible, ideally in some useful way. For example, I could store the objects in an array. Then I could simply say vehicles[0] to get the Ford Focus entry, vehicles[1] to get the Suzuki Swift entry, etc. However, how do I know which entry is the Ford Focus? I want to simply ask "find me Jim's Ford Focus" and have the object returned to me, as fast as possible. For example, in another language, I might use a hash table, indexed by name. How can I do this in javascript? Or, is there a better way? Thanks.

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• Autocomplete and IE7 - slowness, sluggishness as overall pagesize grows?

  - by wchrisjohnson

  Hi, I have the autocomplete plugin (http://bassistance.de/jquery-plugins/jquery-plugin-autocomplete/, version 1.1 and 1.0.2) on a project to add pieces of "equipment" to a "project". On a fresh project the plugin works great; the data returned from the database comes back FAST, you can scroll the list fast, and can select an item and move on to the next one. Once I have a project established with equipment on it, and I go to add equipment, the performance is pretty bad. It takes 4-5 seconds to get the list of data back from the server, scrolling the list is painful, and the cursor takes several seconds to settle on an item. Repainting the page after the list goes away is slow. This is occurring in IE7, latest version. FF3 and Chrome are fine, very snappy. The pagesize is about 40K overall. I'm thinking this is an issue with the IE7 Javascript engine, or an edge case with this plugin and IE7; it works quickly enough in FF3+. I would appreciate any ideas, solutions, known issues, or thoughts on how to more specifically pin this down. I'd love to post sample code, but this is a corporate app, and I'm not how useful it would be given that the server side piece cannot be shown; ie: you can't pull it down and test it like a self contained piece of code.. Thanks in advance! Chris

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• [ebp + 6] instead of +8 in a JIT compiler

  - by David Titarenco

  I'm implementing a simplistic JIT compiler in a VM I'm writing for fun (mostly to learn more about language design) and I'm getting some weird behavior, maybe someone can tell me why. First I define a JIT "prototype" both for C and C++: #ifdef __cplusplus typedef void* (*_JIT_METHOD) (...); #else typedef (*_JIT_METHOD) (); #endif I have a compile() function that will compile stuff into ASM and stick it somewhere in memory: void* compile (void* something) { // grab some memory unsigned char* buffer = (unsigned char*) malloc (1024); // xor eax, eax // inc eax // inc eax // inc eax // ret -> eax should be 3 /* WORKS! buffer[0] = 0x67; buffer[1] = 0x31; buffer[2] = 0xC0; buffer[3] = 0x67; buffer[4] = 0x40; buffer[5] = 0x67; buffer[6] = 0x40; buffer[7] = 0x67; buffer[8] = 0x40; buffer[9] = 0xC3; */ // xor eax, eax // mov eax, 9 // ret 4 -> eax should be 9 /* WORKS! buffer[0] = 0x67; buffer[1] = 0x31; buffer[2] = 0xC0; buffer[3] = 0x67; buffer[4] = 0xB8; buffer[5] = 0x09; buffer[6] = 0x00; buffer[7] = 0x00; buffer[8] = 0x00; buffer[9] = 0xC3; */ // push ebp // mov ebp, esp // mov eax, [ebp + 6] ; wtf? shouldn't this be [ebp + 8]!? // mov esp, ebp // pop ebp // ret -> eax should be the first value sent to the function /* WORKS! */ buffer[0] = 0x66; buffer[1] = 0x55; buffer[2] = 0x66; buffer[3] = 0x89; buffer[4] = 0xE5; buffer[5] = 0x66; buffer[6] = 0x66; buffer[7] = 0x8B; buffer[8] = 0x45; buffer[9] = 0x06; buffer[10] = 0x66; buffer[11] = 0x89; buffer[12] = 0xEC; buffer[13] = 0x66; buffer[14] = 0x5D; buffer[15] = 0xC3; // mov eax, 5 // add eax, ecx // ret -> eax should be 50 /* WORKS! buffer[0] = 0x67; buffer[1] = 0xB8; buffer[2] = 0x05; buffer[3] = 0x00; buffer[4] = 0x00; buffer[5] = 0x00; buffer[6] = 0x66; buffer[7] = 0x01; buffer[8] = 0xC8; buffer[9] = 0xC3; */ return buffer; } And finally I have the main chunk of the program: void main (int argc, char **args) { DWORD oldProtect = (DWORD) NULL; int i = 667, j = 1, k = 5, l = 0; // generate some arbitrary function _JIT_METHOD someFunc = (_JIT_METHOD) compile(NULL); // windows only #if defined _WIN64 || defined _WIN32 // set memory permissions and flush CPU code cache VirtualProtect(someFunc,1024,PAGE_EXECUTE_READWRITE, &oldProtect); FlushInstructionCache(GetCurrentProcess(), someFunc, 1024); #endif // this asm just for some debugging/testing purposes __asm mov ecx, i // run compiled function (from wherever *someFunc is pointing to) l = (int)someFunc(i, k); // did it work? printf("result: %d", l); free (someFunc); _getch(); } As you can see, the compile() function has a couple of tests I ran to make sure I get expected results, and pretty much everything works but I have a question... On most tutorials or documentation resources, to get the first value of a function passed (in the case of ints) you do [ebp+8], the second [ebp+12] and so forth. For some reason, I have to do [ebp+6] then [ebp+10] and so forth. Could anyone tell me why?

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