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<html><head> <title>Operating Systems FAQ :: Linkers</title> <link rel=stylesheet type="text/css" href="default.css"></head><body><TABLE border="0" width="100%"> <TR> <TD><H2><A name="linkers">Linkers</A></H2> </TD> </TR> <TR> <TD>Traditionally, you can't get far without a linker, and thats a fact. <p>Linkers are important tools in the production of an Operating System. <p>They come in many flavours sizes shapes and formats. Some are flexable and some are not. <p>There are important considerations to make when using a linker. <ul> <li><a href="#l1_1">Does it support the output formats I require?</a> <li><a href="#l1_2">Does it support the input formats I'm using?</a> <li><a href="#l1_3">Can I specify address ranges for code and data?</a> <li><a href="#l1_4">Can I produce flat binary files?</a> <li><a href="#l1_5">Can it handle 32bit code?</a> </ul> <p><a name="l1_1"><b>Does it support the output formats I require</b></a> <p>Some linkers only support one kind of output file format, others support every kind of format know to exist. Formats are often not proprietory, having specifications available means if you wish to use Win32/PE file format, you are not required to use Microsoft's Linker. <p><a name="l1_2"><b>Does it support the input formats I'm using?</b></a> <p>This can be important if your going to mix files around. For example, stock DJGPP distribution works with COFF files, and if you link in a TASM assembled OBJ/OMF file, DJGPP(LD) will not recognised it. <p>This is usually of less a concern than the other requirements. <p><a name="l1_3"><b>Can I specify address ranges for code and data?</b></a> <p>This can be very, very important! Especially if you want to product flat binary files. (Like an unrelocated kernel image). You need to be able to specify where the code starts and sometimes where the data begins. <p><a name="l1_4"><b>Can I produce flat binary files?</b></a> <p>As with the above option, this can be important, even if you only need to use it a couple of times. <p><a name-"l1_5"><b>Can it handle 32bit code?</b></a> <p>You might think this a redundant question in the age of "32bit" but there are many custom linkers out there that can't handle 32bit object files. </TD> </TR></TABLE><p> <TABLE border="0" width="100%"> <TR> <TD><H2><A name="linkers_jloc">Linkers :: JLoc</A></H2> </TD> </TR> <TR> <TD>JLoc is written by John Fines. <p> <pre>"This program is a linker/locator for use when you need morecontrol over placement of sections within the image, than a standardlinker provides." </pre> <p>JLoc can be tricky to use for first timers. Carefull reading of the documentation is required. Its not a get-up-and-go linker like all the other linkers. JLoc _requires_ you to write a custome script for each "executable" image you want to link. <p>JLoc gives you flexibility over HOW the object files are linked, regarding loaded addresses and so-forth. <p>JLoc can be obtained here, <a href="http://www.erols.com/johnfine/">http://www.erols.com/johnfine/</a> <p>needs more review!! <p><b>Pros</b> <ul> <li>Supports OMF/OBJ, DJGPP/COFF <li>Supports 32bit code <li>Supports flat binary file generation <li>Handles library files (OMF/OBJ) <li>OMF/OBJ debugging information <li>Free </ul> <p><b>Cons</b> <ul> <li>Does not support any output file formats other than flat binary and DOS/COM <li>Confusing to use for beginners <li>Can't create shared libraries </ul> </TD> </TR></table><p> <TABLE border="0" width="100%"> <TR> <TD><H2><A name="linkers_alink">Linkers :: ALink</A></H2> </TD> </TR> <TR> <TD>ALink (Anthony's Linker) was written as a companion to NASM, its aim to provide a Free linker that supports Nasm's output formats and support some of the more popular executable formats. <p>ALink can be obtained here, <a href="http://www.geocities.com/SiliconValley/Network/4311/index.html">http://www.geocities.com/SiliconValley/Network/4311/index.html</a> <p>need more of a review!! <p><b>Pros</b> <ul> <li>Its Free <li>Supports input formats OMF/OBJ, Win32/COFF Objects <li>Supports output as DOS/COM, DOS/EXE, Win32/PE <li>Can build Win32/PE DLL files <li>Can set the code address <li>Suppots .LIB (OBJ) Library files </ul> <p><b>Cons</b> <ul> <li>Doesnt support flat binary images <li>Strips debugging information <li>Can't create shared libraries </ul> </TD> </TR></table><p> <TABLE border="0" width="100%"> <TR> <TD><H2><A name="linkers_ld">Linkers :: LD (GNU)</A></H2> </TD> </TR> <TR> <TD>LD, the King of linkers. Supports more input and output formats than any other linker in existance. Also the most flexable of the listed linkers. Supports custom linking via scripts. Its advanced featers are hard to use if you dont know what you are doing. <p>LD has the most going for it in terms of functionality compared to the other linkers (Thats _my_ opinion anyway...) but lacking OMF/OBJ support is a BIG omission. <p>This description is based on the LD sources, that can compile to support all formats. Please be aware that the LD that comes with DJGPP is very limited in its output formats (DJGPP/COFF, A.Out, flat binary) and so to with the LD that is part of Linux etc. <p><b>Pros</b> <ul> <li>Supports most known input formats (Elf, DJGPP/COFF, Win32/COFF, A.Out, etc) <li>Supports most known output formats (Elf, Win32/PE, A.Out, COFF, etc) <li>Supports creation of shared libraries <li>Can create flat binary files <li>Can specify code/data addresses <li>Supports DWARF and ECOFF and STABS debugging information <li>Its Free </ul> <p><b>Cons</b> <ul> <li>Does not support OMF/OBJ file format <li>Can get complex writing custom linking scripts <li>Can't create shared libraries </ul> </TD> </TR></table><p> <TABLE border="0" width="100%"> <TR> <TD><H2><A name="linkers_tlink">Linkers :: TLink / TLink32 (Borland)</A></H2> </TD> </TR> <TR> <TD>TLink is the linker that comes with Borland C and their assembler TASM. The difference between TLink and TLink32 is that TLink32 creates ONLY Win32/PE (and DLL) files where as TLink creates Dos and Win16 files. <p><b>Pros</b> <ul> <li>Supports Win32/COFF and OMF/OBJ <li>Has support for libraries <li>Supports creating Win32/PE files and DLL's <li>Supports OMF/OBJ (and DWARF?) debugging information </ul> <p><b>Cons</b> <ul> <li>Lacking in both input and output fileformats <li>Can't create flat binary images <li>Can't create shared libraries </ul> </TD> </TR></table><p> <TABLE border="0" width="100%"> <TR> <TD><H2><A name="linkers_link">Linkers :: Link / NLink (Microsoft)</A></H2> </TD> </TR> <TR> <TD>There are really three fundamentally different linkers.<p>Versions 1.x through 3.x can only produce DOS output. Technically, the_really_ early ones can only produce .com files, and IIRC, starting with2.x they can also produce .exe files.<p>Starting with version 4.x, MS Link can also produce NE format output files.These accept OMF/OBJ format with some MS extensions.<p>Starting with version 6.x, MS link can produce only PE format output files.<p>These accept either COFF/PE or 32-bit OMF/OBJ format object files andproduce (only) PE files as output. They support a few things missing fromthe Borland linker such as the ability to specify the entry point. Debugformats supported include COFF and CodeView.<p>Here I should note that I'm listing only the relatively mainstream versionsof MS link. They've also produced versions that produce various otherformats of output, mostly for OS/2 and/or Windows 3.x VxDs (e.g. LE and LXformat). </TD> </TR></table><p> <TABLE border="0" width="100%"> <TR> <TD><H2><A name="linkers_val">Linkers :: VAL</A></H2> </TD> </TR> <TR> <TD>VALink is an old old linker that has been floating around for ages. It is showing its age quite well. <p><b>There exists an Enhnaced VALink that needs a review!</b> <p><b>Pros</b> <ul> <li>Its free <li>Supports makeing DOS/EXE files. </ul> <p><b>Cons</b> <ul> <li>Can ONLY handle 16bit code. </ul> </TD> </TR></table><p> <TABLE border="0" width="100%"> <TR> <TD><H2><A name="linkers_wlink">Linkers :: WLink (Watcom Linker)</A></H2> </TD> </TR> <TR> <TD>WLink is the linker that comes with Watcom C/C++. Supports a wide range of options and is flexable to a degree. <p>But it can be quite braindead at times and its support for generating ELF files is broken and seriously flawed. <p><b>Pros</b> <ul> <li>Supports range of input formats, OMF/OBJ, Win32/COFF, ELF <li>Supports library files <li>Supports many output file formats from EXE, LE, Win32/PE, Novell NLM files, Pharlap files, QNX, OS2, etc. <li>Handles setting code offset address <li>Supports Watcom, Codeview and Dward debugging information </ul> <p><b>Cons</b> <ul> <li>ELF output is broken <li>Cant do flat binary files </ul> </TD> </TR></table><p> <TABLE border="0" width="100%"> <TR> <TD><H2><A name="linkers_comp">Comparisson</A></H2> </TD> </TR> <TR> <TD> <table border="1" cellspacing="1" cellpadding="4" nowrap> <tr> <th nowrap>Name</th> <th nowrap>Input</th> <th nowrap>Output</th> <th>Flat Binary Images</th> <th nowrap>Set Code<br>Address</th> <th nowrap>Library<br>Support</th> <th>Supports Debug Info</th> <th>32bit Code</th> </tr> <tr> <td>JLoc</td> <td align="CENTER">OMF/OBJ</td> <td align="CENTER">DOS/COM</td> <td align="CENTER">Y</td> <td align="CENTER">Y</td> <td align="CENTER">N</td> <td align="CENTER">OMF/OBJ</td> <td align="CENTER">Y</td> </tr> <tr> <td>ALink</td> <td align="CENTER">OMF/OBJ<br>Win32/COFF<br>DJGPP/COFF</td> <td align="CENTER">DOS/COM<br>DOS/EXE<br>Win32/PE<br>Win32/DLL</td> <td align="CENTER">N</td> <td align="CENTER">Y</td> <td align="CENTER">Y</td> <td align="CENTER">N</td> <td align="CENTER">Y</td> </tr> <tr> <td>LD</td> <td align="CENTER">OMF/OBJ<br>OMF/COFF<br>DJGPP/COFF<br>Win32/COFF<br>A.OUT<br>ELF</td> <td align="CENTER">ELF<br>A.OUT<br>Win32/PE<br>Win32/DLL<br>+more</td> <td align="CENTER">Y</td> <td align="CENTER">Y</td> <td align="CENTER">Y</td> <td align="CENTER">ECOFF<br>DWARF<br>STABS</td> <td align="CENTER">Y</td> </tr> <tr> <td>Tlink<br>Tlink32</td> <td align="CENTER">OMF/OBJ<br>Win32/COFF</td> <td align="CENTER">DOS/EXE<br>DOS/COM<br>Win32/DLL<br>Win32/PE</td> <td align="CENTER">N</td> <td align="CENTER">Y</td> <td align="CENTER">Y</td> <td align="CENTER">OMF/OBJ</td> <td align="CENTER">Y</td> </tr> <tr> <td>Link<br>NLink</td> <td align="CENTER">OMF/OBJ, Win32/COFF</td> <td align="CENTER">DOS/EXE<br>DOS/COM<BR>Win32/PE<br>Win32/DLL<br>LE</td> <td align="CENTER">N</td> <td align="CENTER">Y</td> <td align="CENTER">Y</td> <td align="CENTER">CODEVIEW<br>DWARF</td> <td align="CENTER">Y</td> </tr> <tr> <td>Val</td> <td align="CENTER">OMF/OBJ</td> <td align="CENTER">DOS/EXE</td> <td align="CENTER">N</td> <td align="CENTER">N</td> <td align="CENTER">N</td> <td align="CENTER">Y</td> <td align="CENTER">N</td> </tr> <tr> <td>Wlink</td> <td align="CENTER">OMF/OBJ<br>Win32/COFF<br>ELF</td> <td align="CENTER">DOS/EXE<br>DOS/COM<br>LE<br>ELF<br>Win32/PE<br>Win32/DLL<br>Pharlap<br>Novell NLM<br>Causeway<br>QNX</td> <td align="CENTER">N</td> <td align="CENTER">Y</td> <td align="CENTER">Y</td> <td align="CENTER">WATCOM<br>CODEVIEW<br>DWARF</td> <td align="CENTER">Y</td> </tr> </table> </td> </tr></table></body></html>⌨️ 快捷键说明
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