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Re: [Qemu-devel] best way to implement emulation of AArch64 tagged addre

From: Richard Henderson
Subject: Re: [Qemu-devel] best way to implement emulation of AArch64 tagged addresses
Date: Sat, 9 Apr 2016 08:57:55 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.7.1

On 04/08/2016 05:29 PM, Thomas Hanson wrote:
Looking at tcg_out_tlb_load():
If I'm reading the pseudo-assembler of the function names correctly, it looks
like in the i386 code we're already masking the address being checked:
     tgen_arithi(s, ARITH_AND + trexw, r1, TARGET_PAGE_MASK | (aligned ? s_mask
: 0), 0);
where  TARGET_PAGE_MASK is a simple all-1's mask in the appropriate upper bits.

Can we just poke some 0's into that mask in the tag locations?

No, because we'd no longer have a sign-extended 32-bit value, as fits in that immediate operand field. To load the constant you're asking for, we'd need a 64-bit move insn and another register.


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