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From: Peter Maydell <peter.maydell@linaro.org>
Date: Thu, 12 Nov 2015 16:10:04 +0000
Message-ID: <CAFEAcA9OVTCupHNjHCokcm6Teo+RNq7MTCC2DREEMFHWwai5hA@mail.gmail.com>
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Subject: Re: [Qemu-devel] [PATCH 1/4] target-tilegx: Add fpu header file
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To: Chen Gang <xili_gchen_5257@hotmail.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>, qemu-devel <qemu-devel@nongnu.org>, Richard Henderson <rth@twiddle.net>

On 12 November 2015 at 16:04, Chen Gang <xili_gchen_5257@hotmail.com> wrote:
> On 11/12/15 22:34, Richard Henderson wrote:
>> On 11/08/2015 06:43 AM, Chen Gang wrote:
>>
>>> +#if !defined(HOST_WORDS_BIGENDIAN)
>>> +    /* According to float(uns)sisf2 and float(uns)sidf2 in gcc tilegx.md */
>>> +    uint64_t exp : 8;             /* exp, 0x9e: 31 + TILEGX_F_EXP_FZERO */
>>> +    uint64_t uiknown0 : 2;        /* unknown */
>>
>> I would really rather you didn't use bitfields, because of exactly this sort of endianness problem.  Because, really, you can't trust this layout.  But I won't press this point, because it is complicated enough already.
>>
>
> Because of endianess issues, for me, I don't like bit fields either. But
> I can not find any other simpler ways than current.

> OK, I shall remove them.
>
>>> +#pragma pack(pop)
>>
>> Huh?  What are you attempting to do here?
>>
>
> It is for matching "#pragma pack(push, 1)" which is above all related
> struct/unions in this header file.

Please don't use 'pragma pack' or bitfields. If you need to pack
and unpack things from a target-CPU defined field use bit operations
and/or extract32/deposit32/extract64/deposit64.

thanks
-- PMM