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Date: Fri, 1 Jul 2011 16:15:09 +0200
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From: Laurent Desnogues <laurent.desnogues@gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
Subject: Re: [Qemu-devel] [HelenOS-devel] [sparc64] Miscomputed minimum of a
 group of numbers in sparc64 emulation
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To: Jakub Jermar <jakub@jermar.eu>
Cc: HelenOS development mailing list <helenos-devel@lists.modry.cz>, qemu-devel@nongnu.org

On Fri, Jul 1, 2011 at 2:57 PM, Jakub Jermar <jakub@jermar.eu> wrote:
[...]
> When _not_ singlestepping via GDB's `stepi`, the testcase will fail and
> crash Qemu like this:
>
> qemu: fatal: Trap 0x0101 while trap level (5) >= MAXTL (5), Error state
> <register dumped here>
>
> On the other hand, when I attach GDB to Qemu and step through all
> instructions using `stepi`, the testcase will succeed and crash Qemu
> like this:
>
> qemu: fatal: Trap 0x0100 while trap level (5) >= MAXTL (5), Error state
> <registers dumped here>
>
> Mind the difference in the trap type - 0x100 for success, 0x101 for failure.
>
> This is how I run the test:
>
> Without GDB:
> $ qemu-system-sparc64 -bios ./testcase
>
> With GDB:
> $ qemu-system-sparc64 -bios ./testcase -s -S
>
> From another terminal:
> $ /usr/local/cross/sparc64/bin/sparc64-linux-gnu-gdb
> (gdb) set architecture sparc:v9
> (gdb) target remote localhost:1234
> (gdb) stepi
> ...
>
> Hope this helps to fix the problem.

You don't have to use gdb to reproduce the issue, just add -singlestep
when running qemu.

I find it odd that udivx is using cpu_cc_src and cpu_cc_src2.  Using
dedicated local temps seems to fix the issue.

HTH,

Laurent