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study/tools/SourceBrowser/lxr/lxr-0.3.1/lxr-0.3/http/blurb.html
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study/tools/SourceBrowser/lxr/lxr-0.3.1/lxr-0.3/http/blurb.html
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
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<HTML>
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<HEAD>
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<TITLE>Linux Cross-Reference</TITLE>
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</HEAD>
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<BODY BGCOLOR=WHITE>
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<H1 ALIGN=CENTER>
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Cross-Referencing Linux<BR>
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<A HREF="http:source/">
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<I>Browse the code</I></A></H1>
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<HR><H2>Motivation</H2>
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The Linux Cross-Reference project is the testbed application of a
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general hypertext cross-referencing tool. (Or the other way around.)
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<P>
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The main goal of the project is to create a versatile
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cross-referencing tool for relatively large code repositories. The
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project is based on stock web technology, so the codeview client may
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be chosen from the full range of available web browsers. On the
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server side, any Unix-based web server with cgi-script capability
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should do nicely.
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<P>
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The main feature of the indexer is of course the ability to jump
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easily to the declaration of any global identifier. Indeed, even all
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<I>references</I> to global identifiers are indexed. Quick access to
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function declarations, data (type) definitions and preprocessor macros
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makes code browsing just that tad more convenient. At-a-glance
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overview of e.g. which code areas that will be affected by changing a
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function or type definition should also come in useful during
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development and debugging.
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<P>
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Other bits of hypertextual sugar, such as e-mail and include file
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links, are provided as well, but is on the whole, well, sugar. Some
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minimal visual markup is also done. (Style sheets are considered as a
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way to do this in the future.)
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<HR><H2>Technicalities</H2>
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The index generator is written in <A HREF="http://www.perl.org">Perl</A>
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and relies heavily on Perl's regular expression facilities. The
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algorithm used is very brute force and extremely sloppy. The
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rationale behind the sloppiness is that too little information renders
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the database useless, while too much information simply means the
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users have to think and navigate at the same time.
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<P>
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The Linux source code, with which the project has initially been
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linked, presents the indexer with some very tough obstacles.
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Specifically, the heavy use of preprocessor macros makes the parsing a
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virtual nightmare. We want to index the information in the
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preprocessor directives as well as the actual C code, so we have to
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parse both at once, which leads to no end of trouble. (Strict parsing
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is right out.) Still, we're pretty satisfied with what the indexer
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manages to get out of it.
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<P>
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There's also the question of actually broken code. We want to
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reasonably index all code portions, even if some of it is not entirely
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syntactically valid. This is another reason for the sloppiness.
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<P>
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There are obviously disadvantages to this approach. No scope checking
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is done, and the most annoying effect of this is mistaking local
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identifers for references to global ones with the same name. This
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particular problem (and others) can only be solved by doing (almost)
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full parsing. The feasibility of combining this with the fuzzy way
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indexing is currently done is being looked into.
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<P>
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An identifier is a macro, typedef, struct, enum, union, function,
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function prototype or variable. For the Linux source code between
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50000 and 60000 identifiers are collected. The individual files of the
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sourcecode are formatted on the fly and presented with clickable
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identifiers.
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<P>
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It is possible to search among the identifiers and the entire
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kernel source text. The freetext search is implemented using <A
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HREF="http://glimpse.cs.arizona.edu">Glimpse</A>, so all the
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capabilities of Glimpse are available. Especially the regular expression
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search capabilities are useful.
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<HR><H2>Availability</H2>
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The code for the indexer is released under the
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<A HREF="http://www.gnu.org">GNU</A>
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<A HREF="http://www.gnu.org/copyleft/copyleft.html">Copyleft</A>
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license. Go to <A HREF="http://lxr.linux.no">LXR main site</A> to
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get the latest version.
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<HR><H2>Contacting the authors</H2>
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We would very much like to receive feedback on this project. If you
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find it useful or have suggestions on how to make improvements, feel
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free to send us e-mail. We hope that this will be a useful tool, both
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for experienced developers and beginners wanting to explore the Linux
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sourcecode.
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<HR>
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<ADDRESS>
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<A HREF="mailto:lxr@linux.no">
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Arne Georg Gleditsch and Per Kristian Gjermshus</A>
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</ADDRESS>
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</BODY>
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</HTML>
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