svn commit: r47756 - head/zh_TW.UTF-8/books/handbook/basics
Li-Wen Hsu
lwhsu at FreeBSD.org
Sat Nov 7 18:19:28 UTC 2015
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 <raycherng at gmail.com>
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>
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