svn commit: r47756 - head/zh_TW.UTF-8/books/handbook/basics
Li-Wen Hsu <[email protected]>
| Newsgroups | gmane.os.freebsd.devel.cvs.doc |
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| Message-ID | <[email protected]> |
Author: lwhsu (ports committer) Date: Sat Nov 7 18:19:27 2015 New Revision: 47756 URL: https://svnweb.freebsd.org/changeset/doc/47756 Log: Remove the binary format section of Traditoinal Chinese handbook chapter 3 Unix basics. This was removed from the English version in r42604 in 2013, Submitted by: RayCherng Yu <[email protected]> Approved by: wblock Differential Revision: https://reviews.freebsd.org/D4081 Modified: head/zh_TW.UTF-8/books/handbook/basics/chapter.xml Modified: head/zh_TW.UTF-8/books/handbook/basics/chapter.xml ============================================================================== --- head/zh_TW.UTF-8/books/handbook/basics/chapter.xml Sat Nov 7 17:51:58 2015 (r47755) +++ head/zh_TW.UTF-8/books/handbook/basics/chapter.xml Sat Nov 7 18:19:27 2015 (r47756) @@ -2925,146 +2925,6 @@ Swap: 256M Total, 38M Used, 217M Free, 1 </sect2> </sect1> - <sect1 xml:id="binary-formats"> - <title>Binary 的格式</title> - - <para>若要知道為何 &os; 是採用 &man.elf.5; 格式，必先瞭解當前 &unix; - 系統中三種<quote>影響最為重大</quote>的可執行檔相關背景：</para> - - <itemizedlist> - <listitem> - <para>&man.a.out.5;</para> - - <para>最古老、<quote>經典</quote> 的 &unix; object 檔格式。 - It uses a short and compact header with a magic - number at the beginning that is often used to characterize - the format (see &man.a.out.5; for more details). It - contains three loaded segments: .text, .data, and .bss plus - a symbol table and a string table.</para> - </listitem> - - <listitem> - <para><acronym>COFF</acronym></para> - - <para>The SVR3 object format. The header now comprises a - section table, so you can have more than just .text, .data, - and .bss sections.</para> - </listitem> - - <listitem> - <para>&man.elf.5;</para> - - <para>The successor to <acronym>COFF</acronym>, featuring - multiple sections and 32-bit or 64-bit possible values. One - major drawback: <acronym>ELF</acronym> was also designed - with the assumption that there would be only one ABI per - system architecture. That assumption is actually quite - incorrect, and not even in the commercial SYSV world (which - has at least three ABIs: SVR4, Solaris, SCO) does it hold - true.</para> - - <para>FreeBSD tries to work around this problem somewhat by - providing a utility for <emphasis>branding</emphasis> a - known <acronym>ELF</acronym> executable with information - about the ABI it is compliant with. See the manual page for - &man.brandelf.1; for more information.</para> - </listitem> - </itemizedlist> - - <para>FreeBSD comes from the <quote>classic</quote> camp and used - the &man.a.out.5; format, a technology tried and proven through - many generations of BSD releases, until the beginning of the 3.X - branch. Though it was possible to build and run native - <acronym>ELF</acronym> binaries (and kernels) on a FreeBSD - system for some time before that, FreeBSD initially resisted the - <quote>push</quote> to switch to <acronym>ELF</acronym> as the - default format. Why? Well, when the Linux camp made their - painful transition to <acronym>ELF</acronym>, it was not so much - to flee the <filename>a.out</filename> executable format as it - was their inflexible jump-table based shared library mechanism, - which made the construction of shared libraries very difficult - for vendors and developers alike. Since the - <acronym>ELF</acronym> tools available offered a solution to the - shared library problem and were generally seen as <quote>the way - forward</quote> anyway, the migration cost was accepted as - necessary and the transition made. FreeBSD's shared library - mechanism is based more closely on Sun's - &sunos; style shared library mechanism - and, as such, is very easy to use.</para> - - <para>So, why are there so many different formats?</para> - - <para>Back in the dim, dark past, there was simple hardware. This - simple hardware supported a simple, small system. <filename>a.out</filename> was - completely adequate for the job of representing binaries on this - simple system (a PDP-11). As people ported &unix; from this simple - system, they retained the <filename>a.out</filename> format because it was sufficient - for the early ports of &unix; to architectures like the Motorola - 68k, VAXen, etc.</para> - - <para>Then some bright hardware engineer decided that if he could - force software to do some sleazy tricks, then he would be able - to shave a few gates off the design and allow his CPU core to - run faster. While it was made to work with this new kind of - hardware (known these days as <acronym>RISC</acronym>), <filename>a.out</filename> - was ill-suited for this hardware, so many formats were developed - to get to a better performance from this hardware than the - limited, simple <filename>a.out</filename> format could - offer. Things like <acronym>COFF</acronym>, - <acronym>ECOFF</acronym>, and a few obscure others were invented - and their limitations explored before things seemed to settle on - <acronym>ELF</acronym>.</para> - - <para>In addition, program sizes were getting huge and disks (and - physical memory) were still relatively small so the concept of a - shared library was born. The VM system also became more - sophisticated. While each one of these advancements was done - using the <filename>a.out</filename> format, its usefulness was - stretched more and more with each new feature. In addition, - people wanted to dynamically load things at run time, or to junk - parts of their program after the init code had run to save in - core memory and swap space. Languages became more sophisticated - and people wanted code called before main automatically. Lots of - hacks were done to the <filename>a.out</filename> format to - allow all of these things to happen, and they basically worked - for a time. In time, <filename>a.out</filename> was not up to - handling all these problems without an ever increasing overhead - in code and complexity. While <acronym>ELF</acronym> solved many - of these problems, it would be painful to switch from the system - that basically worked. So <acronym>ELF</acronym> had to wait - until it was more painful to remain with - <filename>a.out</filename> than it was to migrate to - <acronym>ELF</acronym>.</para> - - <para>However, as time passed, the build tools that FreeBSD - derived their build tools from (the assembler and loader - especially) evolved in two parallel trees. The FreeBSD tree - added shared libraries and fixed some bugs. The GNU folks that - originally wrote these programs rewrote them and added simpler - support for building cross compilers, plugging in different - formats at will, and so on. Since many people wanted to build cross - compilers targeting FreeBSD, they were out of luck since the - older sources that FreeBSD had for <application>as</application> and <application>ld</application> were not up to the - task. The new GNU tools chain (<application>binutils</application>) does support cross - compiling, <acronym>ELF</acronym>, shared libraries, C++ - extensions, etc. In addition, many vendors are releasing - <acronym>ELF</acronym> binaries, and it is a good thing for - FreeBSD to run them.</para> - - <para><acronym>ELF</acronym> is more expressive than <filename>a.out</filename> and - allows more extensibility in the base system. The - <acronym>ELF</acronym> tools are better maintained, and offer - cross compilation support, which is important to many people. - <acronym>ELF</acronym> may be a little slower than <filename>a.out</filename>, but - trying to measure it can be difficult. There are also numerous - details that are different between the two in how they map - pages, handle init code, etc. None of these are very important, - but they are differences. In time support for - <filename>a.out</filename> will be moved out of the <filename>GENERIC</filename> - kernel, and eventually removed from the kernel once the need to - run legacy <filename>a.out</filename> programs is past.</para> - </sect1> - <sect1 xml:id="basics-more-information"> <title>更多資訊</title> _______________________________________________ [email protected] mailing list https://lists.freebsd.org/mailman/listinfo/svn-doc-all To unsubscribe, send any mail to "[email protected]"