Can't set file offset of program header
Guilherme Destefani
gd@helixbrasil.com.br
Mon Mar 8 17:48:00 GMT 2004
Hello.
I'm trying to add a section to an elf file, suitable for execution
(executable or shared library), with a special phdr.p_type (numeric one)
So I've got the default linker script, and made a PHDR definition that
resemble the result made by default by the linker.
The problem is that, if this session has the type PT_LOAD, the linker
calculate the file offset and put the value into p_offset of the program
header just fine, like this:
====================This script====================
PHDRS
{
headers PT_PHDR PHDRS
FLAGS ( 5 ) ;
interp PT_INTERP ;
text PT_LOAD FILEHDR PHDRS ;
data PT_LOAD ;
dynamic PT_DYNAMIC ;
extra PT_LOAD
FLAGS ( 0 ) ;
note PT_NOTE ;
/* eh_frame_hdr PT_GNU_EH_FRAME
FLAGS ( 4 ) ; */
}
====================Result into==(readelf -l)======
LOAD 0x1b1000 0x0820e000 0x0820e000 0x00104 0x00104 0x1000
NOTE 0x000000 0x00000000 0x00000000 0x00000 0x00000 0x4
========================END========================
but if the session has another type (non standard, or even PT_NOTE) the
linker set the p_offset to zero:
====================This script====================
PHDRS
{
headers PT_PHDR PHDRS
FLAGS ( 5 ) ;
interp PT_INTERP ;
text PT_LOAD FILEHDR PHDRS ;
data PT_LOAD ;
dynamic PT_DYNAMIC ;
extra 8
FLAGS ( 0 ) ;
note PT_NOTE ;
/* eh_frame_hdr PT_GNU_EH_FRAME
FLAGS ( 4 ) ; */
}
====================Result into==(readelf -l)======
<unknown>: 8 0x000000 0x0820e000 0x0820e000 0x00104 0x00104 0x1
NOTE 0x000000 0x00000000 0x00000000 0x00000 0x00000 0x4
========================END========================
Please, what I'm doing wrong?
The application user for this test was the gimp,
file app/gimp-1.2 ;ls -lh app/gimp-1.2
app/gimp-1.2: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV),
dynamically linked (uses shared libs), not stripped
-rwxr-xr-x 1 Gui gui 15M Mar 8 14:20 app/gimp-1.2
And I've attached both scripts and the full readelf -l
By the way, if I try to execute the program with some extra area mapped
into memory and the mapping is not writeable, the program segfault. I
know that is a kernel issue, but do you have a clue why this happens?
Thanks in advance,
--
Guilherme Destefani
Computer Engineer
Helix S.A.
gd _at_ helixbrasil _dot_ com _dot_ br
Brazil - Parana - Curitiba
(+5541) 362-1313
-------------- next part --------------
Elf file type is EXEC (Executable file)
Entry point 0x806b47c
There are 7 program headers, starting at offset 52
Program Headers:
Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
PHDR 0x000034 0x08048034 0x08048034 0x000e0 0x000e0 R E 0x4
INTERP 0x000114 0x08048114 0x08048114 0x00034 0x00034 R 0x4
[Requesting program interpreter: /lib/ld-linux.so.2]
LOAD 0x000000 0x08048000 0x08048000 0x18d9c4 0x18d9c4 R E 0x1000
LOAD 0x18d9e0 0x081d69e0 0x081d69e0 0x2276c 0x37514 RW 0x1000
DYNAMIC 0x1af478 0x081f8478 0x081f8478 0x00110 0x00110 RW 0x4
<unknown>: 8 0x000000 0x0820e000 0x0820e000 0x00104 0x00104 0x1
NOTE 0x000000 0x00000000 0x00000000 0x00000 0x00000 0x4
Section to Segment mapping:
Segment Sections...
00
01 .interp .note.ABI-tag
02 .interp .note.ABI-tag .hash .dynsym .dynstr .gnu.version .gnu.version_r .rel.dyn .rel.plt .init .plt .text .fini .rodata .eh_frame_hdr .eh_frame
03 .data .dynamic .ctors .dtors .jcr .got .bss
04 .dynamic
05 .extra
06
-------------- next part --------------
Elf file type is EXEC (Executable file)
Entry point 0x806b47c
There are 7 program headers, starting at offset 52
Program Headers:
Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
PHDR 0x000034 0x08048034 0x08048034 0x000e0 0x000e0 R E 0x4
INTERP 0x000114 0x08048114 0x08048114 0x00034 0x00034 R 0x4
[Requesting program interpreter: /lib/ld-linux.so.2]
LOAD 0x000000 0x08048000 0x08048000 0x18d9c4 0x18d9c4 R E 0x1000
LOAD 0x18d9e0 0x081d69e0 0x081d69e0 0x2276c 0x37514 RW 0x1000
DYNAMIC 0x1af478 0x081f8478 0x081f8478 0x00110 0x00110 RW 0x4
LOAD 0x1b1000 0x0820e000 0x0820e000 0x00104 0x00104 0x1000
NOTE 0x000000 0x00000000 0x00000000 0x00000 0x00000 0x4
Section to Segment mapping:
Segment Sections...
00
01 .interp .note.ABI-tag
02 .interp .note.ABI-tag .hash .dynsym .dynstr .gnu.version .gnu.version_r .rel.dyn .rel.plt .init .plt .text .fini .rodata .eh_frame_hdr .eh_frame
03 .data .dynamic .ctors .dtors .jcr .got .bss
04 .dynamic
05 .extra
06
-------------- next part --------------
/* Script for -z combreloc: combine and sort reloc sections + md5 hash sections*/
OUTPUT_FORMAT("elf32-i386", "elf32-i386",
"elf32-i386")
OUTPUT_ARCH(i386)
ENTRY(_start)
SEARCH_DIR("/usr/i386-redhat-linux/lib"); SEARCH_DIR("/usr/lib"); SEARCH_DIR("/usr/local/lib"); SEARCH_DIR("/lib");
/* Do we need any of these for elf?
__DYNAMIC = 0; */
PHDRS
{
headers PT_PHDR PHDRS
FLAGS ( 5 ) ;
interp PT_INTERP ;
text PT_LOAD FILEHDR PHDRS ;
data PT_LOAD ;
dynamic PT_DYNAMIC ;
extra 8 /*PT_LOAD*/
FLAGS ( 0 ) ;
note PT_NOTE ;
/* eh_frame_hdr PT_GNU_EH_FRAME
FLAGS ( 4 ) ; */
}
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END_TEXT = ABSOLUTE (.) - MEM_OFFSET ;
/* Adjust the address for the data segment. We want to adjust up to
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}
-------------- next part --------------
/* Script for -z combreloc: combine and sort reloc sections + md5 hash sections*/
OUTPUT_FORMAT("elf32-i386", "elf32-i386",
"elf32-i386")
OUTPUT_ARCH(i386)
ENTRY(_start)
SEARCH_DIR("/usr/i386-redhat-linux/lib"); SEARCH_DIR("/usr/lib"); SEARCH_DIR("/usr/local/lib"); SEARCH_DIR("/lib");
/* Do we need any of these for elf?
__DYNAMIC = 0; */
PHDRS
{
headers PT_PHDR PHDRS
FLAGS ( 5 ) ;
interp PT_INTERP ;
text PT_LOAD FILEHDR PHDRS ;
data PT_LOAD ;
dynamic PT_DYNAMIC ;
extra PT_LOAD
FLAGS ( 0 ) ;
note PT_NOTE ;
/* eh_frame_hdr PT_GNU_EH_FRAME
FLAGS ( 4 ) ; */
}
SECTIONS
{
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. = 0x08048000;
MEM_OFFSET = ABSOLUTE (.) ;
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*/crtn.o(.init_array .fini_array .preinit_array)
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