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Re: [Qemu-devel] [PATCH 4/5] tcg: reorder removal from lists in tb_phys_

From: Richard Henderson
Subject: Re: [Qemu-devel] [PATCH 4/5] tcg: reorder removal from lists in tb_phys_invalidate
Date: Mon, 28 Mar 2016 17:17:41 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0

On 03/28/2016 01:58 PM, Paolo Bonzini wrote:

On 28/03/2016 20:42, Sergey Fedorov wrote:
On 17/03/16 16:46, address@hidden wrote:
First the translation block is invalidated, for which a simple write
to tb->pc is enough.  This means that cpu-exec will not pick up anymore
the block, though it may still execute it through chained jumps.  This
also replaces the NULLing out of the pointer in the CPUs' local cache.

Although, using 'tb->pc' to mark a TB as invalid is probably not such a
good idea. There may be some cases when PC could become equal to -1. For
example, ARMv6-M uses PC >= 0xFFFFFFF0 to perform exception return. So
we'd better introduce a separate 'tb->valid' or 'tb->invalid' flag.

It is also possible to use tb->flags for that.  I suspect that all-ones
tb flags is never valid, but it could also be a #define.

That might work by accident, but it might not. You'd need to reserve a bit across all of the targets.


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