From: Grant Edwards <grante@visi.com>
To: ecos-discuss@sources.redhat.com
Subject: [ECOS] How to stop gcc padding structs???
Date: Sun, 28 Jan 2001 10:37:00 -0000 [thread overview]
Message-ID: <20010128124058.A9989@visi.com> (raw)
I'm again fighting with gcc trying (and failing) to get it to
stop putting padding bytes into structs. Have any eCosians
figured out how to prevent gcc from padding structs?
I ran into this problem before and gave up, finally having to
use hand-calculated constants instead of "sizeof (struct foo)"
in numerous places. For example, it's impossible to define an
Ethernet header structure that ends up having a size of 14
bytes!
In the following example, gcc insists that each of the "high"
structs occupies four bytes despite my putting a "packed"
attribute evryplace that doesn't generate a syntax warning.
typedef struct
{
volatile unsigned char data __attribute__((packed));
volatile unsigned char _xxx __attribute__((packed));
} high __attribute((packed));
typedef struct
{
high a __attribute__((packed));
high b __attribute__((packed));
high c __attribute__((packed));
} tDemo __attribute__((packed));
tDemo foo;
void *addr[] =
{
&foo,
&foo.a,
&foo.b,
&foo.c
};
testit: file format elf32-bigarm
Disassembly of section .data:
00008000 <addr>:
8000: 00008010 andeq r8, r0, r0, lsl r0
8004: 00008010 andeq r8, r0, r0, lsl r0
8008: 00008014 andeq r8, r0, r4, lsl r0
800c: 00008018 andeq r8, r0, r8, lsl r0
--
Grant Edwards
grante@visi.com
next reply other threads:[~2001-01-28 10:37 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-01-28 10:37 Grant Edwards [this message]
2001-01-29 0:27 ` Andrew Lunn
2001-01-29 7:24 ` Grant Edwards
2001-01-29 9:49 ` Jonathan Larmour
2001-01-29 9:53 ` Grant Edwards
2001-01-29 14:15 ` Jesper Skov
2001-01-28 13:34 Lewin A.R.W. Edwards
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