section manipulation directive--- .previous

博客围绕.previous指令的含义展开讨论，包含发件人、收件人、主题、日期等信息，发件人为Alan Modra，收件人为qiao guopei，日期是2000年8月4日周五。

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Quoted from: http://sources.redhat.com/ml/binutils/2000-08/msg00043.html
-------------------------------------

Re: means of .previous directive

To: qiao guopei <qiaogp at krdl dot org dot sg>
Subject: Re: means of .previous directive
From: Alan Modra <alan at linuxcare dot com dot au>
Date: Fri, 4 Aug 2000 21:23:56 +1000 (EST)
cc: binutils at sourceware dot cygnus dot com

On Fri, 4 Aug 2000, qiao guopei wrote:

> I saw a lot of .previous directive is used in Linux kernel. But I can
> not find the definition of .previous directive in GAS document. Could
> anyone help me?

It changes the current section (ie. where instructions/data are output) to
the previous section.  At least, that is the case when .popsection isn't
used.  Things are a little more complicated when .pushsection/.popsection
are used as .pushsection/.popsection saves/restores both the current
section and it's previous section.

eg. (from the gas elf testsuite)

 .data
	.byte 0
 .section A
	.byte 1
 .previous
	.byte 0
 .previous
	.byte 1
 .pushsection B
	.byte 2
 .previous
	.byte 1
 .previous
	.byte 2
 .pushsection C
	.byte 3
 .previous
	.byte 2
 .previous
	.byte 3
 .popsection
	.byte 2
 .previous
	.byte 1
 .previous
	.byte 2
 .popsection
	.byte 1
 .previous
	.byte 0
 .previous
	.byte 1

will put all the 0's in section .data, all the 1's in section A, all the
2's in section B, and all the 3's in section C

Alan Modra
-- 
Linuxcare.  Support for the Revolution.