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  • $Id tag in comment headers

    - by Bernhard
    When I read source from open source projects I often find a comment line with "$Id" at the header of the file, f. ex.: // $Id: addappwindowa.c 30792 2009-03-07 22:40:04Z neil $ Is there an "offical" syntax for this lines? (What does "30792" means? ) Are there editors that auto-generate these "$Id"s? Are there any tools that use this information?

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  • Dealing with whitespace in SVN?

    - by Eric the Red
    All of the SVN shops I've worked in have a strict rule - replace all tabs with spaces, to avoid whitespace conflicts and variations of tabs in different editors. Is this a very common standard? Does it really make a huge difference, and is it worth the trouble to push this standard to a group of developers new to SVN?

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  • Creating websites: Code by hand or use a visual editor?

    - by Peak
    What is currently the best way to code a (semi complicated) website that uses html, css, javascript and some server stuff (php?)? Would you code most of it by hand, use a visual editor for certains parts, are there standard quality editors nowadays? How do web developers go about doing this?

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  • whats is the fastest-best PHP IDE on windows?

    - by vegatron
    hi I've tried a few php IDEs , but still searching for the FASTEST one all Java based IDEs are too slow, I have 2 computers to work, my home pc which is too fast, and my laptop witch is good , but cant handle a heave software. and I have to work on them both, so I'm looking for the best free ide which is fast I'm not talking about text-editors , because I already have np++ and its great, but looking for extra features to help me save time.. any tips?

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  • Is it possible to figure out (approximately) what line of source code a kernel module is hung on, fr

    - by Mike Heinz
    I'm trying to debug what appears to be a completion queue issue: Apr 14 18:39:15 ST2035 kernel: Call Trace: Apr 14 18:39:15 ST2035 kernel: [<ffffffff8049b295>] schedule_timeout+0x1e/0xad Apr 14 18:39:15 ST2035 kernel: [<ffffffff8049a81c>] wait_for_common+0xd5/0x13c Apr 14 18:39:15 ST2035 kernel: [<ffffffffa01ca32b>] ib_unregister_mad_agent+0x376/0x4c9 [ib_mad] Apr 14 18:39:16 ST2035 kernel: [<ffffffffa03058f4>] ib_umad_close+0xbd/0xfd Is it possible to turn those hex numbers into something close to line numbers?

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  • Python indentation in "empty lines"

    - by niscy
    Which is preferred ("." indicating whitespace)? A) def foo(): x = 1 y = 2 .... if True: bar() B) def foo(): x = 1 y = 2 if True: bar() My intuition would be B (that's also what vim does for me), but I see people using A) all the time. Is it just because most of the editors out there are broken?

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  • "Distance" between colours in PHP

    - by Phil
    I'm looking for a function that can accurately represent the distance between two colours as a number or something. For example I am looking to have an array of HEX values or RGB arrays and I want to find the most similar colour in the array for a given colour eg. I pass a function a RGB value and the 'closest' colour in the array is returned

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  • What do these characters do in a URL/WebAddress?

    - by acidzombie24
    I notice these characters are all illegal #%<>?\/*+|:" I notice these are encoded (%NN where NN is the hex value) but can be replace without problem $,;=& @ (note the space which is typically encoded as + (but may be %20)) #%?/+ i understand. But whats do the following characters do? <>\*|": Note: I understand what : does in the domain part (its the port) as @ is a login but after the first / why is : illegal? (@ isnt)

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  • Audible Audio (.aa) file spec?

    - by Adam
    Does anyone know of a good resource on the Audible Audio (.aa) file spec? I'm trying to write a program that can use them, if no one knows of a resource, any tips on reverse engineering the spec my self? I opened it up in a Hex editor and poked around, looks like an MP3 but with a ton more header info.

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  • Is there a good GUI SVN app for Mac (better than XCode)

    - by Lawrence Johnston
    Hey everybody, I'm looking for a more robust and fully featured GUI SVN manager for Mac than what is built into XCode (which works, but only as long as you don't need anything beyond the bare basics and doesn't work for versioning scripts and such created in other editors). I can use the terminal commands, but I'd really like the option of using a GUI. On windows I use TortoiseSVN and Visual SVN, which do pretty much everything I need, but as far as I'm aware there's nothing even remotely resembling those on the Mac side.

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  • How can I have my python file show its mercurial tag or revision as the module version?

    - by Chris R
    I'd like to add a --version command line option to my python application that will show the right version depending on the tagged status of the command: If the file comes from a version whose short hex ID was abcdef01 that was tagged TAG, --version should show this: MyApp Version TAG (abcdef01) If the file comes from the tip, --version should show this: MyApp (tip) If the file comes from an arbitrary, untagged revision abcdef02, --version should show this: MyApp (development, abcdef02) Is this possible? If so, how?

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  • How is the result of openssl_sign() encoded?

    - by Bozho
    The docs about openssl_sign() say that the signature is returned in the passed string argument. My question is - how is it encoded? Base64, Hex-string, anything else? I don't have php installed and I have to use this PHP code I was given simply in order to verify whether my Java implementation is correct, so don't ask me "have you tried it" ;)

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  • Useful software for netbook?

    - by Moayad Mardini
    I'm looking for recommendations of good software that are particularly useful for netbooks. Software that run great on small screens and low CPU/RAM requirments. I'll start off with the following : Operating Systems: Ubuntu Netbook Remix. Easy Peasy: A fork of Ubuntu Netbook Remix that was once called UBuntu EEE. It isn't just for eeePCs though. Definitely worth a look if vanilla Netbook Remix isn't cutting it. (MarkM) Damn Small Linux (Source) Windows 7: With trimming the installation or compressing the Windows directory to fit on an 8GB SSD. (Will Eddins) nLite: A utility to install a lightweight version of Windows XP without the unnecessary components (like Media Player, Internet Explorer, Outlook Express, MSN Explorer, Messenger...). Utilites: TouchFreeze: To disable the touch pad while typing (Source) InSSIDer: Not only does it make it easier to find and keep a wireless connection, but it turns a netbook into the perfect mobile tool for troubleshooting wireless networks. (phenry) AltMove: Adds more functionality to your mouse for interacting with windows. (Rob) ASUS Font Resizer Utility and other tools by ASUS, specific to ASUS Eee PC series. Internet: Run FileZilla FTP client for a small screen : You can hide a lot of FileZilla's interface parts in the View menu, even the directory trees. Go into Settings = Interface and move the message log next to the transfer queue, if you haven't hidden them both or you want to see them. Select a theme with 16x16 icons. (Source) IDEs and Text Editors: Best lightweight IDE/Text Editor: A question on Stack Overflow that has many good suggestions of IDEs and general text editors for programmers. What’s a good linux C/C++ IDE for a low-res screen?: IDEs for Linux-powered netbooks. Online tools: Dropbox: Since the Netbook has limited disk space, you would like to use Cloud Apps like Dropbox and Ubuntu One so that you don't run out of space especially if you are on a holiday. Later when you go back to your desktop with big hard disk,you can take out the files from your dropbox repo. (Manish Sinha) Google products: like Docs, Calendar and Reader (aviraldg) Web sites and software lists: Netbookfiles.com: Netbook specific software downloads. Software Apps to Maximise your Netbook Battery Power: Netbooks are known for their portability. Not only are they small and lightweight but with their increased power efficiency, batteries can last much longer than conventional laptops. This also means you no longer have to carry a power adapter with you! Several brands emphasis the longevity of the battery as a strong selling point, and for those people who travel a lot, it sure is. Free Must-Have Netbook Apps: Finding software for netbooks can present challenges due to limited hard drive space, processor power, RAM, and screen real-estate. That doesn't mean you have to do without essential programs. The apps below cover all the bases -- entertainment, productivity, security, and communication -- without compromising on performance or usability. Best of all, they're free! Useful Netbook Software: With short battery lives and small resolution screens Netbooks, unlike many other computers on the market, could so with some specific software for their use. Now, not all of those I’ve found are specifically designed for Netbooks, but all are relevant. And they’re designed for Windows XP. The question is community wiki, so feel free to edit it. Updated, thank you all for suggestions.

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  • Setting up RADIUS + LDAP for WPA2 on Ubuntu

    - by Morten Siebuhr
    I'm setting up a wireless network for ~150 users. In short, I'm looking for a guide to set RADIUS server to authenticate WPA2 against a LDAP. On Ubuntu. I got a working LDAP, but as it is not in production use, it can very easily be adapted to whatever changes this project may require. I've been looking at FreeRADIUS, but any RADIUS server will do. We got a separate physical network just for WiFi, so not too many worries about security on that front. Our AP's are HP's low end enterprise stuff - they seem to support whatever you can think of. All Ubuntu Server, baby! And the bad news: I now somebody less knowledgeable than me will eventually take over administration, so the setup has to be as "trivial" as possible. So far, our setup is based only on software from the Ubuntu repositories, with exception of our LDAP administration web application and a few small special scripts. So no "fetch package X, untar, ./configure"-things if avoidable. UPDATE 2009-08-18: While I found several useful resources, there is one serious obstacle: Ignoring EAP-Type/tls because we do not have OpenSSL support. Ignoring EAP-Type/ttls because we do not have OpenSSL support. Ignoring EAP-Type/peap because we do not have OpenSSL support. Basically the Ubuntu version of FreeRADIUS does not support SSL (bug 183840), which makes all the secure EAP-types useless. Bummer. But some useful documentation for anybody interested: http://vuksan.com/linux/dot1x/802-1x-LDAP.html http://tldp.org/HOWTO/html_single/8021X-HOWTO/#confradius UPDATE 2009-08-19: I ended up compiling my own FreeRADIUS package yesterday evening - there's a really good recipe at http://www.linuxinsight.com/building-debian-freeradius-package-with-eap-tls-ttls-peap-support.html (See the comments to the post for updated instructions). I got a certificate from http://CACert.org (you should probably get a "real" cert if possible) Then I followed the instructions at http://vuksan.com/linux/dot1x/802-1x-LDAP.html. This links to http://tldp.org/HOWTO/html_single/8021X-HOWTO/, which is a very worthwhile read if you want to know how WiFi security works. UPDATE 2009-08-27: After following the above guide, I've managed to get FreeRADIUS to talk to LDAP: I've created a test user in LDAP, with the password mr2Yx36M - this gives an LDAP entry roughly of: uid: testuser sambaLMPassword: CF3D6F8A92967E0FE72C57EF50F76A05 sambaNTPassword: DA44187ECA97B7C14A22F29F52BEBD90 userPassword: {SSHA}Z0SwaKO5tuGxgxtceRDjiDGFy6bRL6ja When using radtest, I can connect fine: > radtest testuser "mr2Yx36N" sbhr.dk 0 radius-private-password Sending Access-Request of id 215 to 130.225.235.6 port 1812 User-Name = "msiebuhr" User-Password = "mr2Yx36N" NAS-IP-Address = 127.0.1.1 NAS-Port = 0 rad_recv: Access-Accept packet from host 130.225.235.6 port 1812, id=215, length=20 > But when I try through the AP, it doesn't fly - while it does confirm that it figures out the NT and LM passwords: ... rlm_ldap: sambaNTPassword -> NT-Password == 0x4441343431383745434139374237433134413232463239463532424542443930 rlm_ldap: sambaLMPassword -> LM-Password == 0x4346334436463841393239363745304645373243353745463530463736413035 [ldap] looking for reply items in directory... WARNING: No "known good" password was found in LDAP. Are you sure that the user is configured correctly? [ldap] user testuser authorized to use remote access rlm_ldap: ldap_release_conn: Release Id: 0 ++[ldap] returns ok ++[expiration] returns noop ++[logintime] returns noop [pap] Normalizing NT-Password from hex encoding [pap] Normalizing LM-Password from hex encoding ... It is clear that the NT and LM passwords differ from the above, yet the message [ldap] user testuser authorized to use remote access - and the user is later rejected...

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  • dvd drive I/O error?

    - by bobby
    i get dis error evry time i burn a cd/dvd thru my dvd drive...!! Nero Burning ROM bobby 4C85-200E-4005-0004-0000-7660-0800-35X3-0000-407M-MX37-**** (*) Windows XP 6.1 IA32 WinAspi: - NT-SPTI used Nero Version: 7.11.3. Internal Version: 7, 11, 3, (Nero Express) Recorder: Version: UL01 - HA 1 TA 1 - 7.11.3.0 Adapter driver: HA 1 Drive buffer : 2048kB Bus Type : default CD-ROM: Version: 52PP - HA 1 TA 0 - 7.11.3.0 Adapter driver: HA 1 === Scsi-Device-Map === === CDRom-Device-Map === ATAPI-CD ROM-DRIVE-52MAX F: CdRom0 HL-DT-ST DVDRAM GSA-H12N G: CdRom1 ======================= AutoRun : 1 Excluded drive IDs: WriteBufferSize: 83886080 (0) Byte BUFE : 0 Physical memory : 958MB (981560kB) Free physical memory: 309MB (317024kB) Memory in use : 67 % Uncached PFiles: 0x0 Use Inquiry : 1 Global Bus Type: default (0) Check supported media : Disabled (0) 11.6.2010 CD Image 10:43:02 AM #1 Text 0 File SCSIPTICommands.cpp, Line 450 LockMCN - completed sucessfully for IOCTL_STORAGE_MCN_CONTROL 10:43:02 AM #2 Text 0 File Burncd.cpp, Line 3186 HL-DT-ST DVDRAM GSA-H12N Buffer underrun protection activated 10:43:02 AM #3 Text 0 File Burncd.cpp, Line 3500 Turn on Disc-At-Once, using CD-R/RW media 10:43:02 AM #4 Text 0 File DlgWaitCD.cpp, Line 307 Last possible write address on media: 359848 ( 79:59.73) Last address to be written: 318783 ( 70:52.33) 10:43:02 AM #5 Text 0 File DlgWaitCD.cpp, Line 319 Write in overburning mode: NO (enabled: CD) 10:43:02 AM #6 Text 0 File DlgWaitCD.cpp, Line 2988 Recorder: HL-DT-ST DVDRAM G SA-H12N; CDR co de: 00 97 27 18; O SJ entry from: Pla smon Data systems Ltd. ATIP Data: Special Info [hex] 1: D0 00 A0, 2: 61 1B 12 (LI 97:27.18), 3: 4F 3B 4A ( LO 79:59.74) Additional Info [hex] 1: 00 00 00 (invalid), 2: 00 00 00 (invalid), 3: 00 0 0 00 (invalid) 10:43:02 AM #7 Text 0 File DlgWaitCD.cpp, Line 493 Protocol of DlgWaitCD activities: TRM_DATA_MODE1, 2048, config 0, wanted index0 0 blocks, length 318784 blo cks [G: HL-DT-ST DVDRAM GSA-H12N] -------------------------------------------------------------- 10:43:02 AM #9 Text 0 File ThreadedTransferInterface.cpp, Line 986 Prepare [G: HL-DT-ST DVDRAM GSA-H12N] for write in CUE-sheet-DAO DAO infos: ========== MCN: "" TOCType: 0x00; Se ssion Clo sed, disc fixated Tracks 1 to 1: Idx 0 Idx 1 Next T rk 1: TRM_DATA_MODE1, 2048/0x00, FilePos 0 307200 6531768 32, ISRC "" DAO layout: =========== ___Start_|____Track_|_Idx_|_CtrlAdr_|_____Size_|______NWA_|_RecDep__________ -150 | lead-in | 0 | 0x41 | 0 | 0 | 0x00 -150 | 1 | 0 | 0x41 | 0 | 0 | 0x00 0 | 1 | 1 | 0x41 | 318784 | 318784 | 0x00 318784 | lead-out | 1 | 0x41 | 0 | 0 | 0x00 10:43:02 AM #10 Text 0 File SCSIPTICommands.cpp, Line 240 SPTILockVolume - completed successfully for FSCTL_LOCK_VOLUME 10:43:02 AM #11 Text 0 File Burncd.cpp, Line 4286 Caching options: cache CDRom or Network-Yes, small files-Yes ( ON 10:43:03 AM #19 Text 0 File MMC.cpp, Line 18034 CueData, Len=32 41 00 00 14 00 00 00 00 41 01 00 10 00 00 00 00 41 01 01 10 00 00 02 00 41 aa 01 14 00 46 34 22 10:43:03 AM #20 Text 0 File ThreadedTransfer.cpp, Line 268 Pipe memory size 83836800 10:43:16 AM #21 Text 0 File Cdrdrv.cpp, Line 1405 10:43:16.806 - G: HL-DT-ST DVDRAM GSA-H12N : Queue again later 10:43:42 AM #22 SPTI -1502 File SCSIPassThrough.cpp, Line 181 CdRom1: SCSIStatus(x02) WinError(0) NeroError(-1502) Sense Key: 0x04 (KEY_HARDWARE_ERROR) Nero Report 2 Nero Burning ROM Sense Code: 0x08 Sense Qual: 0x03 CDB Data: 0x2A 00 00 00 4D 00 00 00 20 00 00 00 Sense Area: 0x70 00 04 00 00 00 00 10 53 29 A1 80 08 03 Buffer x0c7d9a40: Len x10000 0xDC 87 EB 41 6E AC 61 5A 07 B2 DB 78 B5 D4 D9 24 0x8D BC 51 38 46 56 0F EE 16 15 5C 5B E3 B0 10 16 0x14 B1 C3 6E 30 2B C4 78 15 AB D5 92 09 B7 81 23 10:43:42 AM #23 CDR -1502 File Writer.cpp, Line 306 DMA-driver error, CRC error G: HL-DT-ST DVDRAM GSA-H12N 10:43:55 AM #24 Phase 38 File dlgbrnst.cpp, Line 1767 Burn process failed at 48x (7,200 KB/s) 10:43:55 AM #25 Text 0 File SCSIPTICommands.cpp, Line 287 SPTIDismountVolume - completed successfully for FSCTL_DISMOUNT_VOLUME 10:44:01 AM #26 Text 0 File Cdrdrv.cpp, Line 11412 DriveLocker: UnLockVolume completed 10:44:01 AM #27 Text 0 File SCSIPTICommands.cpp, Line 450 UnLockMCN - completed sucessfully for IOCTL_STORAGE_MCN_CONTROL Existing drivers: Registry Keys: HKLM\Software\Microsoft\Windows NT\CurrentVersion\WinLogon Nero Report 3

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  • Strange enduser experience with Liferay, Glassfish and Apache on RedHat

    - by Pete Helgren
    Tried multiple forums to get to the bottom of this. I hope I can get some direction here: Here is the stack I am working with: Red Hat Enterprise Linux Server release 5.6 (Tikanga) Liferay 6.0.6 on Glassfish 3.0.1 MySQL 5.0.77 Apache 2.2.3 The Liferay portal provides a variety of portlets to end users. Static content (web pages), static resources (primarily pdf and mp3 files 1mb - 80mb in size), File upload and download capabilities (primarily 40-60mb mp3 files) and online streaming of those MP3 files. Here is the strange end user experiences: Under normal load: (20-30) users uploading, downloading or streaming files and 20-30 accessing static content (some of it downloads), we see the following: 1) Clicking a link triggers the download of a portion of an MP3 (the portion is a few seconds long). 2) Clicking on a link tiggers the download of the page content rather than rendering. 3) Clicking a link causes the page to dump binary data to the end user rather than the expected content. 4) Clicking a link returns the text of a javascript file rather than rendering the page. Each occurrence is totally random (or appears so). Sometimes it works, sometimes it doesn't. It seems to have no relation to browser or client OS. The strange events seem to occur much more frequently when using an SSL connection rather than regular http. Apache serves as a proxy server only (reverse). It basically passes all the requests through to Glassfish. There isn't any static content proxy served by Apache. We rebuilt the entire stack from scratch and redeployed the portlet wars and still have the same issues. Liferay is running as a single server (not clustered). We disabled mod_cache in Apache. The problems are more frequent as the server load grows. This morning the load is pretty light and we are seeing few problems but the use of the site will grow, particularly tonight around 9pm CST through Wednesday morning. You could try the site (http://preview.bsfinternational.org) during those times and I would expect that you might experience one of the weirdnesses as you randomly click links on the site (https is invoked only when signed in). Again, https seems to exacerbate the issue. This seems very much like a caching issue but I don't know where in the stack to start peeling the onion. Apache? Liferay? Glassfish? MySQL? Maybe even Redhat? We are stumped and most forums we have posted to (LifeRay and Glassfish) have returned very few suggestions. I just need an idea of where to start looking. I understand that we could have a portlet EDIT: Opening the files in a Hex editor that appear to be pages that download rather than render, we see that the first 4000 characters are "junk" and then the "HTTP/1.1 ...." 'normal' header is seen. So something is dumping a jumble of characters up to offset 4000 (when viewing it in a Hex editor). Perhaps a clue? Ideas?

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  • The DOS DEBUG Environment

    - by MarkPearl
    Today I thought I would go back in time and have a look at the DEBUG command that has been available since the beginning of dawn in DOS, MS-DOS and Microsoft Windows. up to today I always knew it was there, but had no clue on how to use it so for those that are interested this might be a great geek party trick to pull out when you want the awe the younger generation and want to show them what “real” programming is about. But wait, you will have to do it relatively quickly as it seems like DEBUG was finally dumped from the Windows group in Windows 7. Not to worry, pull out that Windows XP box which will get you even more geek points and you can still poke DEBUG a bit. So, for those that are interested and want to find out a bit about the history of DEBUG read the wiki link here. That all put aside, lets get our hands dirty.. How to Start DEBUG in Windows Make sure your version of Windows supports DEBUG. Open up a console window Make a directory where you want to play with debug – in my instance I called it C221 Enter the directory and type Debug You will get a response with a – as illustrated in the image below…   The commands available in DEBUG There are several commands available in DEBUG. The most common ones are A (Assemble) R (Register) T (Trace) G (Go) D (Dump or Display) U (Unassemble) E (Enter) P (Proceed) N (Name) L (Load) W (Write) H (Hexadecimal) I (Input) O (Output) Q (Quit) I am not going to cover all these commands, but what I will do is go through a few of them briefly. A is for Assemble Command (to write code) The A command translates assembly language statements into machine code. It is quite useful for writing small assembly programs. Below I have written a very basic assembly program. The code typed out is as follows mov ax,0015 mov cx,0023 sub cx,ax mov [120],al mov cl,[120]A nop R is for Register (to jump to a point in memory) The r command turns out to be one of the most frequent commands you will use in DEBUG. It allows you to view the contents of registers and to change their values. It can be used with the following combinations… R – Displays the contents of all the registers R f – Displays the flags register R register_name – Displays the contents of a specific register All three methods are illustrated in the image above T is for Trace (To execute a program step by step) The t command allows us to execute the program step by step. Before we can trace the program we need to point back to the beginning of the program. We do this by typing in r ip, which moves us back to memory point 100. We then type trace which executes the first line of code (line 100) (As shown in the image below starting from the red arrow). You can see from the above image that the register AX now contains 0015 as per our instruction mov ax,0015 You can also see that the IP points to line 0103 which has the MOV CX,0023 command If we type t again it will now execute the second line of the program which moves 23 in the cx register. Again, we can see that the line of code was executed and that the CX register now holds the value of 23. What I would like to highlight now is the section underlined in red. These are the status flags. The ones we are going to look at now are 1st (NV), 4th (PL), 5th (NZ) & 8th (NC) NV means no overflow, the alternate would be OV PL means that the sign of the previous arithmetic operation was Plus, the alternate would be NG (Negative) NZ means that the results of the previous arithmetic operation operation was Not Zero, the alternate would be ZR NC means that No final Carry resulted from the previous arithmetic operation. CY means that there was a final Carry. We could now follow this process of entering the t command until the entire program is executed line by line. G is for Go (To execute a program up to a certain line number) So we have looked at executing a program line by line, which is fine if your program is minuscule BUT totally unpractical if we have any decent sized program. A quicker way to run some lines of code is to use the G command. The ‘g’ command executes a program up to a certain specified point. It can be used in connection with the the reset IP command. You would set your initial point and then run the G command with the line you want to end on. P is for Proceed (Similar to trace but slightly more streamlined) Another command similar to trace is the proceed command. All that the p command does is if it is called and it encounters a CALL, INT or LOOP command it terminates the program execution. In the example below I modified our example program to include an int 20 at the end of it as illustrated in the image below… Then when executing the code when I encountered the int 20 command I typed the P command and the program terminated normally (illustrated below). D is for Dump (or for those more polite Display) So, we have all these assembly lines of code, but if you have ever opened up an exe or com file in a text/hex editor, it looks nothing like assembly code. The D command is a way that we can see what our code looks like in memory (or in a hex editor). If we examined the image above, we can see that Debug is storing our assembly code with each instruction following immediately after the previous one. For instance in memory address 110 we have int and 111 we have 20. If we examine the dump of memory we can see at memory point 110 CD is stored and at memory point 111 20 is stored. U is for Unassemble (or Convert Machine code to Assembly Code) So up to now we have gone through a bunch of commands, but probably one of the most useful is the U command. Let’s say we don’t understand machine code so well and so instead we want to see it in its equivalent assembly code. We can type the U command followed by the start memory point, followed by the end memory point and it will show us the assembly code equivalent of the machine code. E is for a bunch of things… The E command can be used for a bunch of things… One example is to enter data or machine code instructions directly into memory. It can also be used to display the contents of memory locations. I am not going to worry to much about it in this post. N / L / W is for Name, Load & Write So we have written out assembly code in debug, and now we want to save it to disk, or write it as a com file or load it. This is where the N, L & W command come in handy. The n command is used to give a name to the executable program file and is pretty simple to use. The w command is a bit trickier. It saves to disk all the memory between point bx and point cx so you need to specify the bx memory address and the cx memory address for it to write your code. Let’s look at an example illustrated below. You do this by calling the r command followed by the either bx or cx. We can then go to the directory where we were working and will see the new file with the name we specified. The L command is relatively simple. You would first specify the name of the file you would like to load using the N command, and then call the L command. Q is for Quit The last command that I am going to write about in this post is the Q command. Simply put, calling the Q command exits DEBUG. Commands we did not Cover Out of the standard DEBUG commands we covered A, T, G, D, U, E, P, R, N, L & W. The ones we did not cover were H, I & O – I might make mention of these in a later post, but for the basics they are not really needed. Some Useful Resources Please note this post is based on the COS2213 handouts for UNISA A Guide to DEBUG - http://mirror.href.com/thestarman/asm/debug/debug.htm#NT

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  • Anatomy of a .NET Assembly - PE Headers

    - by Simon Cooper
    Today, I'll be starting a look at what exactly is inside a .NET assembly - how the metadata and IL is stored, how Windows knows how to load it, and what all those bytes are actually doing. First of all, we need to understand the PE file format. PE files .NET assemblies are built on top of the PE (Portable Executable) file format that is used for all Windows executables and dlls, which itself is built on top of the MSDOS executable file format. The reason for this is that when .NET 1 was released, it wasn't a built-in part of the operating system like it is nowadays. Prior to Windows XP, .NET executables had to load like any other executable, had to execute native code to start the CLR to read & execute the rest of the file. However, starting with Windows XP, the operating system loader knows natively how to deal with .NET assemblies, rendering most of this legacy code & structure unnecessary. It still is part of the spec, and so is part of every .NET assembly. The result of this is that there are a lot of structure values in the assembly that simply aren't meaningful in a .NET assembly, as they refer to features that aren't needed. These are either set to zero or to certain pre-defined values, specified in the CLR spec. There are also several fields that specify the size of other datastructures in the file, which I will generally be glossing over in this initial post. Structure of a PE file Most of a PE file is split up into separate sections; each section stores different types of data. For instance, the .text section stores all the executable code; .rsrc stores unmanaged resources, .debug contains debugging information, and so on. Each section has a section header associated with it; this specifies whether the section is executable, read-only or read/write, whether it can be cached... When an exe or dll is loaded, each section can be mapped into a different location in memory as the OS loader sees fit. In order to reliably address a particular location within a file, most file offsets are specified using a Relative Virtual Address (RVA). This specifies the offset from the start of each section, rather than the offset within the executable file on disk, so the various sections can be moved around in memory without breaking anything. The mapping from RVA to file offset is done using the section headers, which specify the range of RVAs which are valid within that section. For example, if the .rsrc section header specifies that the base RVA is 0x4000, and the section starts at file offset 0xa00, then an RVA of 0x401d (offset 0x1d within the .rsrc section) corresponds to a file offset of 0xa1d. Because each section has its own base RVA, each valid RVA has a one-to-one mapping with a particular file offset. PE headers As I said above, most of the header information isn't relevant to .NET assemblies. To help show what's going on, I've created a diagram identifying all the various parts of the first 512 bytes of a .NET executable assembly. I've highlighted the relevant bytes that I will refer to in this post: Bear in mind that all numbers are stored in the assembly in little-endian format; the hex number 0x0123 will appear as 23 01 in the diagram. The first 64 bytes of every file is the DOS header. This starts with the magic number 'MZ' (0x4D, 0x5A in hex), identifying this file as an executable file of some sort (an .exe or .dll). Most of the rest of this header is zeroed out. The important part of this header is at offset 0x3C - this contains the file offset of the PE signature (0x80). Between the DOS header & PE signature is the DOS stub - this is a stub program that simply prints out 'This program cannot be run in DOS mode.\r\n' to the console. I will be having a closer look at this stub later on. The PE signature starts at offset 0x80, with the magic number 'PE\0\0' (0x50, 0x45, 0x00, 0x00), identifying this file as a PE executable, followed by the PE file header (also known as the COFF header). The relevant field in this header is in the last two bytes, and it specifies whether the file is an executable or a dll; bit 0x2000 is set for a dll. Next up is the PE standard fields, which start with a magic number of 0x010b for x86 and AnyCPU assemblies, and 0x20b for x64 assemblies. Most of the rest of the fields are to do with the CLR loader stub, which I will be covering in a later post. After the PE standard fields comes the NT-specific fields; again, most of these are not relevant for .NET assemblies. The one that is is the highlighted Subsystem field, and specifies if this is a GUI or console app - 0x20 for a GUI app, 0x30 for a console app. Data directories & section headers After the PE and COFF headers come the data directories; each directory specifies the RVA (first 4 bytes) and size (next 4 bytes) of various important parts of the executable. The only relevant ones are the 2nd (Import table), 13th (Import Address table), and 15th (CLI header). The Import and Import Address table are only used by the startup stub, so we will look at those later on. The 15th points to the CLI header, where the CLR-specific metadata begins. After the data directories comes the section headers; one for each section in the file. Each header starts with the section's ASCII name, null-padded to 8 bytes. Again, most of each header is irrelevant, but I've highlighted the base RVA and file offset in each header. In the diagram, you can see the following sections: .text: base RVA 0x2000, file offset 0x200 .rsrc: base RVA 0x4000, file offset 0xa00 .reloc: base RVA 0x6000, file offset 0x1000 The .text section contains all the CLR metadata and code, and so is by far the largest in .NET assemblies. The .rsrc section contains the data you see in the Details page in the right-click file properties page, but is otherwise unused. The .reloc section contains address relocations, which we will look at when we study the CLR startup stub. What about the CLR? As you can see, most of the first 512 bytes of an assembly are largely irrelevant to the CLR, and only a few bytes specify needed things like the bitness (AnyCPU/x86 or x64), whether this is an exe or dll, and the type of app this is. There are some bytes that I haven't covered that affect the layout of the file (eg. the file alignment, which determines where in a file each section can start). These values are pretty much constant in most .NET assemblies, and don't affect the CLR data directly. Conclusion To summarize, the important data in the first 512 bytes of a file is: DOS header. This contains a pointer to the PE signature. DOS stub, which we'll be looking at in a later post. PE signature PE file header (aka COFF header). This specifies whether the file is an exe or a dll. PE standard fields. This specifies whether the file is AnyCPU/32bit or 64bit. PE NT-specific fields. This specifies what type of app this is, if it is an app. Data directories. The 15th entry (at offset 0x168) contains the RVA and size of the CLI header inside the .text section. Section headers. These are used to map between RVA and file offset. The important one is .text, which is where all the CLR data is stored. In my next post, we'll start looking at the metadata used by the CLR directly, which is all inside the .text section.

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