Subject: Re: structure alignment on arm in NetBSD? (resend without html)
To: Martin Fouts <>
From: Matt Thomas <>
List: tech-toolchain
Date: 10/15/2007 10:28:04
On Oct 15, 2007, at 9:45 AM, Martin Fouts wrote:

> Deep in the heart of gcc sources,
> In src/gnu/dist/gcc4/gcc/config/arm/netbsd-elf.h I found the comment
> /* VERY BIG NOTE: Change of structure alignment for NetBSD/arm.
>    There are consequences you should be aware of...
>    Normally GCC/arm uses a structure alignment of 32 for compatibility
>    with armcc.  This means that structures are padded to a word
>    boundary.  However this causes problems with bugged NetBSD kernel
>    code (possibly userland code as well - I have not checked every
>    binary).  The nature of this bugged code is to rely on sizeof()
>    returning the correct size of various structures rounded to the
>    nearest byte (SCSI and ether code are two examples, the vm system
>    is another).  This code breaks when the structure alignment is 32
>    as sizeof() will report a word=3Drounded size.  By changing the
>    structure alignment to 8. GCC will conform to what is expected by
>    NetBSD.
> (rest elided...)
> Is this comment still accurate?

Yes.  Also, NetBSD does not use short-enums either.