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Re: [Qemu-devel] qemu on armeb host

From: Josh Parsons
Subject: Re: [Qemu-devel] qemu on armeb host
Date: Mon, 25 Jul 2005 00:15:39 -0700

On Sat, 2005-07-23 at 19:14 +0200, Karel Gardas wrote:

> Interesting! What's the performance of x86 on ARM? I would guess something 
> like 386/16-25MHz? Also are you running on stock nslu2 or have you done 
> un-underclocking and now running on 266MHz?

Yes, this an un-underclocked nslu2.  I haven't run any benchmarks yet -
the real world app I was interested in (gnu prolog) was usably fast,

I attach the patches I needed to build a qemu-i386 linux-user emulator
for armeb.  I've split them into several patches, as the changes are a
little fiddily, and I think they will be more comprehensible split up
and given some explanation.  I'd like to see all of these incorporated
into the mainline qemu sources if possible.

There is only one issue not addressed by the patches: it seems that when
compiling for an arm host with -O2, gcc versions 3.3.5 and 3.3.6 at
least will generate incorrect code for translate-op.c.  I think it is to
do with the very large switch/case construct included from op.h in that
file.  The solution is to compile that file with -fno-schedule-insns,
but as this is apparently a gcc bug, I've not tried to fix it here.

Some explanation of the patches:

arm-bigendian-host.patch modifies arm.ld to allow linking a bigendian
binary if and only if a bigendian host was detected at compile time.

arm-build-fixes.patch brings some of the arm host code up to date with
the rest of qemu.  This would be needed to build for an arm little-
endian host too.

dyngen.patch corrects a bug in dyngen.c that resulted in incorrect
generation of op.h where the build system has a different byte order
from the host.  Not strictly armeb related, but as I am cross-compiling
for armeb on a i386 system, I needed it to build.

op-gen-label.patch addresses a qemu bug that occurs on arm systems, but
is not arm specific. The trouble is the generated code in op.c that
includes "dummy" calls to __op_gen_label1 and friends.  Because
__op_gen_label1 is defined in dyngen.h as a global variable, not a
function, it may be assigned an address at link time that is too far
away from the code in op.c for a relocation to generated.  The result is
a linker error. I've fixed this by using the gcc section attribute to
cause __op_gen_label[1-3] to be located in the text section, where they
can be guaranteed to be close enough to the code in op.c.  I'm not sure
if this is the best solution, but it works for me.  Maybe it would be
more portable to define the __op_gen_label symbols as functions, rather
than variables.

Josh Parsons
Philosophy Department
1238 Social Sciences and Humanities Bldg.
University of California
Davis, CA 95616-8673

Please avoid sending me Word or PowerPoint attachments.
See http://www.gnu.org/philosophy/no-word-attachments.html

Attachment: arm-bigendian-host.patch
Description: Text Data

Attachment: arm-build-fixes.patch
Description: Text Data

Attachment: dyngen.patch
Description: Text Data

Attachment: op-gen-label.patch
Description: Text Data

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