Re: c/507: Incorrect loading of addresses when compiling for PowerPC

[Franz Sirl <Franz dot Sirl-kernel at lauterbach dot com>]

The following reply was made to PR c/507; it has been noted by GNATS.

From: Franz Sirl <Franz.Sirl-kernel@lauterbach.com>
To: martin@malibunetworks.com,
 gcc-gnats@gcc.gnu.org
Cc:  
Subject: Re: c/507: Incorrect loading of addresses when compiling for PowerPC
Date: Wed, 6 Sep 2000 23:51:36 +0200

 On Tue, 05 Sep 2000, martin@malibunetworks.com wrote:
 > >Number:         507
 > >Category:       c
 > >Synopsis:       Incorrect loading of addresses when compiling for PowerPC
 > >Confidential:   no
 > >Severity:       critical
 > >Priority:       medium
 > >Responsible:    unassigned
 > >State:          open
 > >Class:          sw-bug
 > >Submitter-Id:   net
 > >Arrival-Date:   Tue Sep 05 14:26:00 PDT 2000
 > >Closed-Date:
 > >Last-Modified:
 > >Originator:     Martin Usher
 > >Release:        2.9 (ecos), also 2.7.2 (version shipped with Wind River's
 > > "Tornado 2.0" Organization:
 > >Environment:
 >
 > i586/NT4.0 cross compiling for PowerPC
 >
 > >Description:
 >
 > When loading a register with a 32 bit literal such as an address the
 > compiler emits this instruction sequence:-
 >
 > 	addis 9,0,sdata@ha
 > 	addi 0,9,sdata@l
 >
 > where 'sdata' is the address of a label. This will sometimes load the wrong
 > address into r0 because addi sign extends the number - if bit 16 (NOTE -
 > PowerPC uses 0 as LH/MSB so this is the MSB of the lower 16 bits) is set
 > this will sign extend and decrement the high part that had already been
 > loaded into r9.
 >
 > >How-To-Repeat:
 >
 > This is very easy to repeat once you know it is there. Neither compiler
 > options nor processor type affect the output. All you have to do is compile
 > any arbitary piece of code with the -S option to see this all over the
 > emitted code.
 >
 > >Fix:
 >
 > Use ori instead of addi as the second order.
 >
 > Note that GCC uses the 'simplified' order, 'li', in the instruction code
 > instead of addi, so expect the code sequence in the compiler to look like
 > "li reg,value" instead of addi "reg,reg,value"
 
 Have you actually looked at the hex code produced by this assembler code? The 
 @ha should correctly load a preadjusted high part of the address. Doesn't 
 this happen for you and your binutils?.
 
 Franz.