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From: HongWoo Lee <hongwoo7@gmail•com>
To: linuxppc-dev@lists•ozlabs.org
Subject: Question about powerpc branch instructions
Date: Fri, 07 Aug 2009 17:47:00 +0900	[thread overview]
Message-ID: <4A7BEA04.7030006@gmail.com> (raw)

Hi~

I want to know about bl instruction and the difference between branch 
instructions.
I found this code segment.

{{{
....
bl  go_to_real
insrdi  r18, r19, 32, 0
....
}}}

And I found the explanation about branch instructions in PowerISA 2.06 
document.

{{{
b target_addr (AA=0 LK=0)
ba target_addr (AA=1 LK=0)
bl target_addr (AA=0 LK=1)
bla target_addr (AA=1 LK=1)

If AA=0 then the branch target address is the sum of LI || 0b00 
sign-extended and the address of this instruction,
with the high-order 32 bits of the branch target address set to 0 in 
32-bit mode.

If AA=1 then the branch target address is the value LI || 0b00 
sign-extended,
with the high-order 32 bits of the branch target address set to 0 in 
32-bit mode.

If LK=1 then the effective address of the instruction following the 
Branch instruction is placed into the Link Register.
}}}

Questions
#1: Is there any special reason to concatenate 0b00 ?  Why 0b00 ??
#2: Is b similar to the jmp in x86 ? and bl is similar to the call in x86 ?

Thanks in advance.

HongWoo.

next             reply	other threads:[~2009-08-07  8:46 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-08-07  8:47 HongWoo Lee [this message]
2009-08-07  8:52 ` Question about powerpc branch instructions Benjamin Herrenschmidt
2009-08-07 19:37 ` Scott Wood

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