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Message-ID: <7f45d93905080212136ecb0cbb@mail.gmail.com>
Date: Tue, 02 Aug 2005 19:13:00 -0000
From: Shaun Jackman <sjackman@gmail.com>
Reply-To: Shaun Jackman <sjackman@gmail.com>
To: Dave Korn <dave.korn@artimi.com>
Subject: Re: memcpy to an unaligned address
Cc: gcc@sources.redhat.com
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	 <SERRANOFlF8HGmCvoXM000000dd@SERRANO.CAM.ARTIMI.COM>
X-SW-Source: 2005-08/txt/msg00074.txt.bz2

On 8/2/05, Dave Korn <dave.korn@artimi.com> wrote:
>   In order for anyone to answer your questions about the alignment of
> various types in a struct, don't you think you should perhaps have told u=
s a
> little about what those types actually are and how the struct is laid out?

Of course, my apologies. I was clearly overly terse. I declare the
structure packed as follows:

typedef struct {
	uint16_t a;
	uint32_t b;
} __attribute__((packed)) st;

void foo(st *s, int n)
{
	memcpy(&s->b, &n, sizeof n);
}

This code generates the unaligend store:
$ arm-elf-objdump -d packed.o
...
   0:   e24dd004        sub     sp, sp, #4      ; 0x4
   4:   e5801002        str     r1, [r0, #2]
   8:   e28dd004        add     sp, sp, #4      ; 0x4
   c:   e12fff1e        bx      lr
$ arm-elf-gcc --version | head -1
arm-elf-gcc (GCC) 4.0.1

Cheers,
Shaun