Re: [Tinycc-devel] Weird bitfield size handling, discrepancy with gcc

[Vincent Lefevre]

On 2016-10-18 09:59:36 +0200, Daniel Glöckner wrote:
> On Tue, Oct 18, 2016 at 09:41:49AM +0200, Vincent Lefevre wrote:
> > AFAIK, both are correct.
> 
> It depends on the ABI. The ARM EABI defines those details in
> http://infocenter.arm.com/help/topic/com.arm.doc.ihi0042f/IHI0042F_aapcs.pdf
> section 7.1.7. But I don't know if we adhere to those rules when
> compiling for ARM.

"For the purposes of calculating the alignment of the aggregate the
type of the member shall be the Fundamental Data Type upon which the
bit-field is based.[1]

[1] The intent is to permit the C construct struct {int a:8; char b[7];}
to have size 8 and alignment 4."

Assuming that there are similar requirements for other architectures,
the behavior of GCC now makes sense to me.

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Vincent Lefèvre <address@hidden> - Web: <https://www.vinc17.net/>
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