A question about head.S

A question about head.S

[Pei-Jie Hong]

In arch/ppc/kernel/head.S, there are lines looks like
bne 4f or b 5f, I know they are branch instructions, but what
about 4f or 5f. Are they the relative length? and what is the unit,
I mean if 4f is a number , is it number of instructions or number
of bytes or words?

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Re: A question about head.S

[Grant Erickson]

>From 'info as':

Local Symbol Names
------------------

   Local symbols help compilers and programmers use names temporarily.
There are ten local symbol names, which are re-used throughout the
program.  You may refer to them using the names `0' `1' ... `9'.  To
define a local symbol, write a label of the form `N:' (where N
represents any digit).  To refer to the most recent previous definition
of that symbol write `Nb', using the same digit as when you defined the
label.  To refer to the next definition of a local label, write
`Nf'--where N gives you a choice of 10 forward references.  The `b'
stands for "backwards" and the `f' stands for "forwards".


--
 Grant M. Erickson                    University of Minnesota Alumni
  o mail:erick205@tc.umn.edu                              1996 BSEE
  o http://www.tc.umn.edu/~erick205/                      1998 MSEE

On Fri, 28 Apr 2000, Pei-Jie Hong wrote:
> In arch/ppc/kernel/head.S, there are lines looks like
> bne 4f or b 5f, I know they are branch instructions, but what
> about 4f or 5f. Are they the relative length? and what is the unit,
> I mean if 4f is a number , is it number of instructions or number
> of bytes or words?


** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/

Re: A question about head.S

[Jerry Van Baren]

You can use numbers for local (temporary) labels followed by 'f' for
forward or 'b' for back.  The instruction bne 4f goes to the label '4'
further down in the program.  If it was bne 4b, it would go to the
label '4' previously seen in the file.  This is good for short logical
jumps and loops.  Use the feature with care, massive confusion
otherwise ensues.

gvb


At 04:29 PM 4/28/00 +0200, Pei-Jie Hong wrote:

>In arch/ppc/kernel/head.S, there are lines looks like
>bne 4f or b 5f, I know they are branch instructions, but what
>about 4f or 5f. Are they the relative length? and what is the unit,
>I mean if 4f is a number , is it number of instructions or number
>of bytes or words?
>


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Re: A question about head.S

[Wolfgang Denk]

In message <3909A05A.E1901D52@cern.ch> you wrote:
>
> In arch/ppc/kernel/head.S, there are lines looks like
> bne 4f or b 5f, I know they are branch instructions, but what
> about 4f or 5f. Are they the relative length? and what is the unit,
> I mean if 4f is a number , is it number of instructions or number
> of bytes or words?

You will also see labels "4:" and "5:" etc. in the text.  "4f"  means
"label  4  searching  forward",  while  "5b"  means "label 5 seaching
backwards".

Wolfgang Denk

--
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd@denx.de
Heavier than air flying machines are impossible.
                    -- Lord Kelvin, President, Royal Society, c. 1895

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