Date: Fri, 8 Jun 2001 17:53:50 -0700 (PDT) From: John Polstra <jdp@polstra.com> To: hackers@freebsd.org Cc: milunovic@sendmail.ru Subject: Re: ELF p_offset & p_vaddr Message-ID: <200106090053.f590roD50858@vashon.polstra.com> In-Reply-To: <Pine.BSF.4.21.0106082028430.1244-100000@scorpion.cosmos.all.net> References: <Pine.BSF.4.21.0106082028430.1244-100000@scorpion.cosmos.all.net>
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In article <Pine.BSF.4.21.0106082028430.1244-100000@scorpion.cosmos.all.net>,
milunovic <milunovic@sendmail.ru> wrote:
>
> I'm little confused.I'm reading ELF specification and I found that
> p_offset and p_vaddr should be congrunet to module PAGE_SIZE.
> So is this correct ? If it isn't can anybody tell me what is correct.
It is correct. It is done that way so that the file can be loaded
into memory simply by mapping it. Mapping occurs on page boundaries.
> #define PAGE_SIZE 4096
> p_offset % PAGE_SIZE == p_vaddr % PAGE_SIZE
Yes, that's correct. For example, notice that the final 3 digits are
the same here in the "VMA" and "File off" columns. PAGE_SIZE == 4096
== 0x1000.
blake$ objdump -h /usr/bin/id
/usr/bin/id: file format elf32-i386
Sections:
Idx Name Size VMA LMA File off Algn
0 .interp 00000019 080480f4 080480f4 000000f4 2**0
CONTENTS, ALLOC, LOAD, READONLY, DATA
1 .note.ABI-tag 00000018 08048110 08048110 00000110 2**2
CONTENTS, ALLOC, LOAD, READONLY, DATA
2 .hash 000000d8 08048128 08048128 00000128 2**2
CONTENTS, ALLOC, LOAD, READONLY, DATA
3 .dynsym 00000230 08048200 08048200 00000200 2**2
CONTENTS, ALLOC, LOAD, READONLY, DATA
4 .dynstr 00000138 08048430 08048430 00000430 2**0
CONTENTS, ALLOC, LOAD, READONLY, DATA
5 .rel.bss 00000010 08048568 08048568 00000568 2**2
CONTENTS, ALLOC, LOAD, READONLY, DATA
6 .rel.plt 00000098 08048578 08048578 00000578 2**2
CONTENTS, ALLOC, LOAD, READONLY, DATA
7 .init 0000000b 08048610 08048610 00000610 2**2
CONTENTS, ALLOC, LOAD, READONLY, CODE
8 .plt 00000140 0804861c 0804861c 0000061c 2**2
CONTENTS, ALLOC, LOAD, READONLY, CODE
9 .text 00000928 0804875c 0804875c 0000075c 2**2
CONTENTS, ALLOC, LOAD, READONLY, CODE
10 .fini 00000006 08049084 08049084 00001084 2**2
CONTENTS, ALLOC, LOAD, READONLY, CODE
11 .rodata 0000035a 080490a0 080490a0 000010a0 2**5
CONTENTS, ALLOC, LOAD, READONLY, DATA
12 .data 0000000c 0804a3fc 0804a3fc 000013fc 2**2
CONTENTS, ALLOC, LOAD, DATA
13 .eh_frame 00000004 0804a408 0804a408 00001408 2**2
CONTENTS, ALLOC, LOAD, DATA
14 .ctors 00000008 0804a40c 0804a40c 0000140c 2**2
CONTENTS, ALLOC, LOAD, DATA
15 .dtors 00000008 0804a414 0804a414 00001414 2**2
CONTENTS, ALLOC, LOAD, DATA
16 .got 00000058 0804a41c 0804a41c 0000141c 2**2
CONTENTS, ALLOC, LOAD, DATA
17 .dynamic 00000088 0804a474 0804a474 00001474 2**2
CONTENTS, ALLOC, LOAD, DATA
18 .bss 00000130 0804a4fc 0804a4fc 000014fc 2**3
ALLOC
19 .comment 000000c8 00000000 00000000 000014fc 2**0
CONTENTS, READONLY
20 .note 00000050 00000000 00000000 000015c4 2**0
CONTENTS, READONLY
John
--
John Polstra jdp@polstra.com
John D. Polstra & Co., Inc. Seattle, Washington USA
"Disappointment is a good sign of basic intelligence." -- Chögyam Trungpa
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