i actually write a shared object loader, which loads with the gcc created shared-objects (ELF) on a cortex-m4 controller. Loading, dependency resolving and relocating etc works fine. But the shared object has some strange symbols in the .dynsym section which i dont know how to handle.
readelf --dyn-sym libfoo.so
Num: Wert Size Typ Bind Vis Ndx Name
0: 00000000 0 NOTYPE LOCAL DEFAULT UND
1: 000005c8 0 SECTION LOCAL DEFAULT 8
2: 00000874 0 SECTION LOCAL DEFAULT 16
3: 00000000 0 NOTYPE GLOBAL DEFAULT UND printf
4: 0000082d 32 FUNC GLOBAL DEFAULT 12 foo3
5: 0000087c 0 NOTYPE GLOBAL DEFAULT 18 __bss_start__
6: 00000000 0 NOTYPE GLOBAL DEFAULT UND __libc_init_array
7: 00000728 0 NOTYPE GLOBAL DEFAULT 12 _mainCRTStartup
8: 000005c8 0 FUNC GLOBAL DEFAULT 8 _init
9: 00000000 0 NOTYPE GLOBAL DEFAULT UND __libc_fini_array
10: 00000000 0 NOTYPE WEAK DEFAULT UND __deregister_frame_info
11: 00000000 0 NOTYPE WEAK DEFAULT UND _ITM_registerTMCloneTable
12: 00000898 0 NOTYPE GLOBAL DEFAULT 18 __bss_end__
13: 00000728 0 NOTYPE GLOBAL DEFAULT 12 _start
14: 00000000 0 NOTYPE WEAK DEFAULT UND software_init_hook
15: 00000000 0 NOTYPE WEAK DEFAULT UND _ITM_deregisterTMCloneTab
16: 00000000 0 NOTYPE GLOBAL DEFAULT UND memset
17: 00000000 0 NOTYPE GLOBAL DEFAULT UND main
18: 00000000 0 NOTYPE WEAK DEFAULT UND hardware_init_hook
19: 000005e0 0 FUNC GLOBAL DEFAULT 9 _fini
20: 00000000 0 NOTYPE GLOBAL DEFAULT UND atexit
21: 00000000 0 NOTYPE WEAK DEFAULT UND __stack
22: 00000000 0 NOTYPE GLOBAL DEFAULT UND exit
23: 00000000 0 NOTYPE WEAK DEFAULT UND _Jv_RegisterClasses
24: 00000000 0 NOTYPE WEAK DEFAULT UND __register_frame_info
Why do the shared object need a reference to a main-function and to the __libc_init_array function? Especially the symbol to __libc_init_array makes no sense to me... This function normaly initializes the __preinit_array, _init and __init_array, but this job should be done by my loader not by the object itself, or i am wrong?
Is there anywhere a step-by-step documentation how to initialize a loaded shared-object with all its dependencies?
This is the way, how i build my shared-object:
gcc -std=gnu99 -W -Wall -Wstrict-prototypes -Wmissing-prototypes -ffunction-sections -fdata-sections -mfloat-abi=soft -mcpu=cortex-m4 -mthumb -mlong-calls -Os -g -c -fPIC -o foo.o foo.c
gcc -shared -fPIC -Wl,-soname,libfoo.so -T./shared.ld -o libfoo.so foo.o
There is just another question: Without the -mlong-calls option, my gcc generates invalid opcode in the .plt section... what i'm doing wrong?
EDIT: My foo.c is verry simple:
#include <stdio.h>
#include <string.h>
void foo3 (void)
{
printf("Hello from shared-object");
}
This is my shared.ld:
OUTPUT_FORMAT("elf32-littlearm", "elf32-bigarm", "elf32-littlearm")
OUTPUT_ARCH(arm)
SECTIONS
{
.interp : { *(.interp) }
.note.ABI-tag : { *(.note.ABI-tag) }
.gnu.version : { *(.gnu.version) }
.gnu.version_d : { *(.gnu.version_d) }
.gnu.version_r : { *(.gnu.version_r) }
.dynamic : { *(.dynamic) }
.hash : { *(.hash) }
.dynsym : { *(.dynsym) }
.dynstr : { *(.dynstr) }
.rel.dyn : { *(.rel.dyn) }
.rela.dyn : { *(.rela.dyn) }
.rel.plt : { *(.rel.plt) }
.rela.plt : { *(.rela.plt) }
.plt : { *(.plt) }
.got : { *(.got.plt) *(.got) }
.init ALIGN(32 / 8) :
{
KEEP (*(.init))
}
.fini ALIGN(32 / 8) :
{
KEEP (*(.fini))
}
.preinit_array ALIGN(32 / 8) :
{
PROVIDE(__preinit_array_start = .);
KEEP (*(.preinit_array))
PROVIDE(__preinit_array_end = .);
}
.init_array ALIGN(32 / 8) :
{
PROVIDE(__init_array_start = .);
KEEP (*(.init_array*))
PROVIDE(__init_array_end = .);
}
.fini_array ALIGN(32 / 8) :
{
PROVIDE(__fini_array_start = .);
KEEP (*(.fini_array*))
PROVIDE(__fini_array_end = .);
}
.text ALIGN(32 / 8) :
{
*(.text .text.*)
}
.rodata ALIGN(32 / 8) :
{
*(.rodata .rodata.*)
}
.data ALIGN(32 / 8) :
{
*(.data .data.*)
}
.bss ALIGN(32 / 8) :
{
PROVIDE(__bss_start__ = .);
*(.bss .bss.*)
*(COMMON)
PROVIDE(__bss_end__ = .);
}
}
NOTICE: The reference to _printf_ is set to the the printf of my main program at linktime - just for testing purpose.
thanks for your help :-)
