this is the problem:
When I link my scripts in C, using ld, when I generate elf32-i386 files as output format in ld, putting it as OUTPUT_FORMAT() in the ld script, I dont have any error, but if I try to put in this last OUTPUT_FORMAT() "binary" or try to output a file with .bin extension, I get a mixture of errors like:
kernel.o: In function `k_main':
kernel.c:(.text+0xe): undefined reference to `_GLOBAL_OFFSET_TABLE_'
kernelutils.o: In function `k_clear_screen':
kernelutils.c:(.text+0xc): undefined reference to `_GLOBAL_OFFSET_TABLE_'
kernelutils.o: In function `k_clear_screen_front':
kernelutils.c:(.text+0x56): undefined reference to `_GLOBAL_OFFSET_TABLE_'
kernelutils.o: In function `k_printf':
kernelutils.c:(.text+0xa0): undefined reference to `_GLOBAL_OFFSET_TABLE_'
kernelutils.o: In function `k_sleep_3sec':
kernelutils.c:(.text+0x152): undefined reference to `_GLOBAL_OFFSET_TABLE_'
kernelmalloc.o:kernelmalloc.c:(.text+0xc): more undefined references to `_GLOBAL_OFFSET_TABLE_' follow
This not only happens when compiling specific scripts, all scripts that try to use ld to link, or gcc since this calls ld, die in the attempt of get a binary with .bin extension.
When showing the symbols of one of the executables (kernel.o in the output of above) I see that the symbol _GLOBAL_OFFSET_TABLE_ isnt defined, and the most scary part, all the functions that returned error in the error output of above have their symbols removed, this is the nm output:
cristian@mymethodman:~/Desktop/kernel/0.0.3/Archivos$ nm kernel.o
U _GLOBAL_OFFSET_TABLE_
U k_clear_screen
U k_clear_screen_front
00000000 T k_main
U k_malloc
U k_printf
U k_sleep_3sec
00000000 T __x86.get_pc_thunk.bx
How I can solve this? I will leave the linker script below to ensure it isn a problem of the .ld file, with both "to get elf" and "to get binary" versions. Thanks in advance!
Ld scripts:
To get binary:
ENTRY(loader)
OUTPUT_FORMAT(binary)
SECTIONS {
/* The kernel will live at 3GB + 1MB in the virtual
address space, which will be mapped to 1MB in the
physical address space. */
. = 0xC0100000;
.text : AT(ADDR(.text) - 0xC0000000) {
*(.text)
*(.rodata*)
}
.data ALIGN (0x1000) : AT(ADDR(.data) - 0xC0000000) {
*(.data)
}
.bss : AT(ADDR(.bss) - 0xC0000000) {
_sbss = .;
*(COMMON)
*(.bss)
_ebss = .;
}
}
To get ELF:
ENTRY(loader)
OUTPUT_FORMAT(elf32-i386)
SECTIONS {
/* The kernel will live at 3GB + 1MB in the virtual
address space, which will be mapped to 1MB in the
physical address space. */
. = 0xC0100000;
.text : AT(ADDR(.text) - 0xC0000000) {
*(.text)
*(.rodata*)
}
.data ALIGN (0x1000) : AT(ADDR(.data) - 0xC0000000) {
*(.data)
}
.bss : AT(ADDR(.bss) - 0xC0000000) {
_sbss = .;
*(COMMON)
*(.bss)
_ebss = .;
}
}
As yo ucan see between both only changes the OUTPUT_FORMAT() line.
-fno-pic
. This is a good reason to use a GCC cross compiler for Operating System development. You can read about creating one here: wiki.osdev.org/GCC_Cross-Compiler – Abutting-fpie
with GCC but the linker is emitting GOT-relative relocation entries. I'm sure I've used an incorrect set of input flags for this to happen (even feeding the binaries into IDA Pro it reports to me that the binary uses "non-standard" relocations!). Any thoughts? Similar to the OP,_GLOBAL_OFFSET_TABLE_
is undefined and there is no.got
section. Indeed removing-fpic
from the argument set prevented the GOT-relative relocations (now ABS) (but still no.got
section). Would you mind helping me to understand? – Hoisch