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Re: [Qemu-devel] [PATCH 2/2] target-mips/translate.c: Add judgement for
From: |
Aurelien Jarno |
Subject: |
Re: [Qemu-devel] [PATCH 2/2] target-mips/translate.c: Add judgement for msb and lsb |
Date: |
Tue, 29 Jul 2014 00:32:36 +0200 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Mon, Jul 28, 2014 at 11:01:02PM +0100, Peter Maydell wrote:
> On 28 July 2014 22:42, Aurelien Jarno <address@hidden> wrote:
> > On Mon, Jul 28, 2014 at 11:58:22PM +0800, Dongxue Zhang wrote:
> >> Use 'if' to make sure the real msb greater than the lsb. As the compiler
> >> may
> >> not do this.
> >
> > What are you trying to fix exactly? These cases are defined as
> > "unpredictable" in the MIPS ISA manual, which is what is implemented in
> > QEMU.
>
> This may be true, but the TCG README doesn't define negative
> lengths as being "unspecified behaviour" (ie guaranteed to at
> least not crash even if the result isn't specified), and in fact the
> implementation of tcg_gen_deposit will assert on negative lengths.
> We shouldn't implement guest unpredictable cases as "crash QEMU".
Well I tried this code under QEMU, and it clearly doesn't crash. It
seems the assert are not enabled with the default configuration options.
That said I agree it's something to avoid, but I don't think triggering
a RI exception is the thing to do (even if it is correct according the
MIPS ISA manual) when real silicon output a random result instead.
--
Aurelien Jarno GPG: 4096R/1DDD8C9B
address@hidden http://www.aurel32.net
- [Qemu-devel] [PATCH 1/2] target-mips/translate.c: Free TCG in OPC_DINSV, Dongxue Zhang, 2014/07/28
- [Qemu-devel] [PATCH 2/2] target-mips/translate.c: Add judgement for msb and lsb, Dongxue Zhang, 2014/07/28
- Re: [Qemu-devel] [PATCH 2/2] target-mips/translate.c: Add judgement for msb and lsb, Aurelien Jarno, 2014/07/28
- Re: [Qemu-devel] [PATCH 2/2] target-mips/translate.c: Add judgement for msb and lsb, Peter Maydell, 2014/07/28
- Re: [Qemu-devel] [PATCH 2/2] target-mips/translate.c: Add judgement for msb and lsb,
Aurelien Jarno <=
- Re: [Qemu-devel] [PATCH 2/2] target-mips/translate.c: Add judgement for msb and lsb, Peter Maydell, 2014/07/28
- Re: [Qemu-devel] [PATCH 2/2] target-mips/translate.c: Add judgement for msb and lsb, Aurelien Jarno, 2014/07/28
- Re: [Qemu-devel] [PATCH 2/2] target-mips/translate.c: Add judgement for msb and lsb, Elta, 2014/07/29
- Re: [Qemu-devel] [PATCH 2/2] target-mips/translate.c: Add judgement for msb and lsb, Aurelien Jarno, 2014/07/29
- Re: [Qemu-devel] [PATCH 2/2] target-mips/translate.c: Add judgement for msb and lsb, Dongxue Zhang, 2014/07/29
- Re: [Qemu-devel] [PATCH 2/2] target-mips/translate.c: Add judgement for msb and lsb, Peter Maydell, 2014/07/29
Re: [Qemu-devel] [PATCH 1/2] target-mips/translate.c: Free TCG in OPC_DINSV, Aurelien Jarno, 2014/07/28