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Re: [Qemu-devel] [PATCH 0/4] tcg: Add debug facilities for TCGv

From: Andreas Färber
Subject: Re: [Qemu-devel] [PATCH 0/4] tcg: Add debug facilities for TCGv
Date: Tue, 13 Dec 2011 14:11:47 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:8.0) Gecko/20111105 Thunderbird/8.0

Am 12.12.2011 16:58, schrieb Paul Brook:
>> For me the most annoying issue was that tcg_gen_qemu_{ld,st}* needs TCGv.
> You mean the value transferred is always TCGv sized, so ld32u requires an 
> additional truncation before doing 32-bit arithmetic?  Fixing that is 
> completely independent of making TCGv a separate type.

tcg_gen_qemu_{ld,st} (guest) differs from tcg_gen_{ld,st} (host) in that
they require a TCGv ret/arg (all use TCGv addr). I.e., to read an 8-bit
memory-mapped register on a 64-bit target with tcg_gen_qemu_ld8u we need
a TCGv temporary and trunc to i32 afterwards (smallest currently
available variable size) or unnecessarily blow up storage size to
target_long/TCGv everywhere.

So, yes, adding an _i32 version may make sense, to at least encapsulate
it at TCG level.

And without my patches I might have not noticed this design flaw. :)


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