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Re: [Qemu-devel] [PATCH, RFC] Disable implicit self-modifying code suppo

From: Fabrice Bellard
Subject: Re: [Qemu-devel] [PATCH, RFC] Disable implicit self-modifying code support for RISC CPUs
Date: Sat, 03 Nov 2007 23:13:45 +0100
User-agent: Thunderbird (X11/20070212)

Blue Swirl wrote:
> Hi,
> RISC CPUs don't support self-modifying code unless the affected area
> is flushed explicitly. This patch disables the extra effort for SMC.
> The changes in this version would affect all CPUs except x86, but I'd
> like to see if there are problems with some target, so that the
> committed change can be limited. Without comments, I'll just disable
> SMC for Sparc, as there are no problems. So please comment, especially
> if you want to "opt in".
> For some reason, I can't disable all TB/TLB flushing, for example
> there was already one line with TARGET_HAS_SMC || 1, but removing the
> || 1 part causes crashing. Does anyone know why?

With the current QEMU architecture, you cannot disable self-modifying
code as you did. This is why I did not fully supported the
TARGET_HAS_SMC flag. The problem is that the translator make the
assumption that the RAM and the TB contents are consistent for example
when handling exceptions. Suppressing this assumption is possible but
requires more work.



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