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Re: [PATCH v1] MIPS: fix vmlinuz build when only 32bit math shell is ava

To: Alexander Clouter <alex@digriz.org.uk>
Subject: Re: [PATCH v1] MIPS: fix vmlinuz build when only 32bit math shell is available
From: Wu Zhangjin <wuzhangjin@gmail.com>
Date: Tue, 19 Jan 2010 18:27:29 +0800
Cc: Ralf Baechle <ralf@linux-mips.org>, linux-mips@linux-mips.org
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References: <42fa29d2007a40a31a0bb8fbf1091e11eb9b5ac2.1263893871.git.wuzhangjin@gmail.com> <20100119095556.GF32413@chipmunk>
Reply-to: wuzhangjin@gmail.com
Sender: linux-mips-bounce@linux-mips.org
Hi,

On Tue, 2010-01-19 at 09:55 +0000, Alexander Clouter wrote:
[...]
> >
> As a passing query, why do we have the high 32bit (0xffffffff....) spiel 
> if later we can just make VMLINU[XZ]_LOAD_ADDRESS the low half?  I see 
> the output of 'nm' shows:
> ----
> alex@berk:/usr/src/wag54g/linux$ nm vmlinux | head -n1
> 941019e4 t .ex0
> alex@berk:/usr/src/wag54g/linux$ nm vmlinuz | head -n1
> 944abb50 B .heap
> ----
> 

Mine:

$ mips64el-unknown-linux-gnu-nm vmlinux | head -n1
ffffffff80202304 t .ex0
$ mips64el-unknown-linux-gnu-nm vmlinuz | head -n1
ffffffff80b174e0 B .heap

and exactly, here is why we need to reserve the high 32bit:

$ cat arch/mips/Makefile | grep ^load | grep -v 0xffffffff
load-$(CONFIG_MIPS_SIM)         += 0x80100000
load-$(CONFIG_SGI_IP27)         += 0xc00000004001c000
load-$(CONFIG_SGI_IP27)         += 0xa80000000001c000
load-$(CONFIG_SGI_IP28)         += 0xa800000020004000

(Hi, Ralf, can we use the low 32bit directly?)

> However I am guessing it's some 64bit CPU requirement as my x86_64 
> kernel seems to have 0xffffffff....  Which raises the question, why is 
> AR7 not just using VMLINUX_LOAD_ADDRESS=0x94100000?
> 
> > 1. Append "the high 32bit of VMLINUX_LOAD_ADDRESS" as the prefix if it
> > exists.
> > 
> > 2. Get the sum of "the low 32bit of VMLINUX_LOAD_ADDRESS + VMLINUX_SIZE"
> > with printf "%08x" (08 herein is used to prefix the result with 0...)
> > 
> > The corresponding shell script is:
> > 
> >   A=$VMLINUX_LOAD_ADDRESS;
> >   # Append "the high 32bit of VMLINUX_LOAD_ADDRESS" as the prefix if it 
> > exists.
> >   [ "${A:0:10}" != "${A}" ] && echo -n ${A:2:8};
> >   # Get the sum of "the low 32bit of VMLINUX_LOAD_ADDRESS + VMLINUX_SIZE"
> >   printf "%08x" $(($VMLINUX_SIZE + 0x${A:(-8)}))
> > 
> Eugh, bash-ism's...
> ----
> alex@berk:/usr/src/wag54g/linux$ bash -c 'A=1234567890; echo ${A:0:5}'
> 12345
> alex@berk:/usr/src/wag54g/linux$ dash -c 'A=1234567890; echo ${A:0:5}'
> dash: Bad substitution
> ----

Ooh! really forget to test it with the dash, dash.... So, this revision
is also broken ;(

> 
> Your 'punishment', use Plan9 for a period of no less than a week! :)
>

I have never played with Plan9, but ubuntu, archlinux, gentoo... and
created my user with "useradd -s /bin/bash ....", so, I only work with
bash ;)

> You have to use the pattern matching approach I used in my original 
> patch, that's portable.  Look at 'man 1 dash' and search for 'substr' 
> for more details.

To consider "portable" and "good-looking", Perhaps it's better to use C
language here ;)

Thanks!

Regards,
        Wu Zhangjin


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