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From: Max Filippov <jcmvbkbc@gmail.com>
Date: Sun, 22 May 2011 16:10:16 +0400
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Subject: Re: [Qemu-devel] [PATCH 21/26] target-xtensa: implement unaligned
	exception option
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To: Richard Henderson <rth@twiddle.net>
Cc: qemu-devel@nongnu.org

> > +static void gen_load_store_alignment(DisasContext *dc, int shift, TCGv_i32 addr)
> > +{
> > +    TCGv_i32 tmp = tcg_temp_local_new_i32();
> > +    tcg_gen_mov_i32(tmp, addr);
> > +    tcg_gen_andi_i32(addr, addr, ~0 << shift);
> > +    if (option_enabled(dc, XTENSA_OPTION_UNALIGNED_EXCEPTION)) {
> > +        int label = gen_new_label();
> > +        tcg_gen_brcond_i32(TCG_COND_EQ, addr, tmp, label);
> > +        gen_exception_cause_vaddr(dc, LOAD_STORE_ALIGNMENT_CAUSE, tmp);
> > +        gen_set_label(label);
> > +    }
> > +    tcg_temp_free(tmp);
> > +}
> 
> This is not the correct method for this.  Set ALIGNED_ONLY before
> defining the softmmu_templates.  Define do_unaligned_access to raise
> the exception.  See e.g. target-sparc/op_helper.c.

There are three alignment possibilities for xtensa: no unaligned exception, unaligned exception and hardware alignment.
In the first case unaligned access silently goes to aligned address. It looks like it cannot be done via do_unaligned_access, can it?
In the third case most unaligned accesses are handled transparently by the hardware. But e.g. unaligned access by multiprocessor synchronization instructions still cause alignment exception. Do I need to implement a different alignment checking mechanism for those unhandled cases?

Thanks.
-- Max