From: Andy Whitcroft <apw@shadowen.org>
Date: Thu, 23 Nov 2006 16:19:14 GMT
Subject: Re: sizeof(struct ...)
Message-ID: <4565CA02.20602@shadowen.org>
In-Reply-To: <4565C8F4.6000606@lsrfire.ath.cx>

René Scharfe wrote:
> Erik Mouw schrieb:
>> On Thu, Nov 23, 2006 at 04:45:09PM +0100, René Scharfe wrote:
>>>  Is there really a compiler that inserts padding between arrays of
>>> unsigned chars?
>> Yes, that compiler is called "gcc".
>>
>> #include <stdio.h>
>>
>> struct foo {
>>         unsigned char a[3];
>>         unsigned char b[3];
>> };
>>
>> int main(void)
>> {
>>         printf("%d\n", sizeof(struct foo));
>>         return 0;
>> }
>>
>> On i386 that prints 6, on ARM it prints 8.
> 
> Does it add 1 byte after a and and 1 after b or two after b?
> I suspect it's the latter case -- otherwise Gerrit's patch,
> which started this thread, wouldn't help solve his problem.
> Or the pad sizing follows complicated rules that I do not
> understand at the moment.
> 
> Time to look for an ARM emulator, it seems.

Perhaps we can look and see what a portable application like gzip or
bzip2 do in this situation.  They must have the same problem.