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x64 gcc: kernel binary grows up to 1MB
Posted: Wed May 10, 2006 11:41 am
by Guest
Hi, i have a problem with linking my kernel with gcc x86_x64.
Always when i link my kernel, it grows up to 1MB.
Yeah i read the article in the OS FAQ.
I wrote following linker script but it doesnt help:
Code: Select all
ENTRY(_start)
SECTIONS
{
.text 0x100000 :
{
code = .; _code = .; __code = .;
*(.text)
. = ALIGN(4096);
}
.data :
{
data = .; _data = .; __data = .;
*(.data)
. = ALIGN(4096);
}
.rodata :
{
rodata = .; _rodata = .; __rodata = .;
*(.rodata)
. = ALIGN(4096);
}
.bss :
{
bss = .; _bss = .; __bss = .;
*(.bss)
. = ALIGN(4096);
}
end = .; _end = .; __end = .;
}
I compile my kernel with following flags:
-ffreestanding -nostdlib -fno-builtin -fomit-frame-pointer -m64 -c -fno-zero-initialized-in-bss
Please help.
Thanks in advance.
Re:x64 gcc: kernel binary grows up to 1MB
Posted: Wed May 10, 2006 12:08 pm
by mystran
First of all, what binary format are you linking into?
Is this a raw binary? Or maybe ELF?
You either need a format that allows you to link sections to different locations at link time, or you need to specify where the binary is loaded, that is, what physical address (within file) corresponds to what logical address.
Re:x64 gcc: kernel binary grows up to 1MB
Posted: Wed May 10, 2006 2:31 pm
by YeXo
Where in the faq did you find that linker script?
I think you schould replace this code
by this
Re:x64 gcc: kernel binary grows up to 1MB
Posted: Thu May 11, 2006 6:46 am
by Guest
Thanks for your replies !
I tried to change it to:
But it still doesnt work.
I forgot to say that I link to ELF.
Re:x64 gcc: kernel binary grows up to 1MB
Posted: Thu May 11, 2006 7:00 am
by Solar
(I would feel much better if you had a name, other than "Guest". Pick a nick and use it, it makes things easier.)
The error doesn't have to be linker-script-related, it could be caused by your assembler code, or any of the commands you use to compile, assemble, and link your code.
Or, to put it like a computer would do: Insufficient input.
Re:x64 gcc: kernel binary grows up to 1MB
Posted: Thu May 11, 2006 10:20 am
by YeXo
Solar wrote:
The error doesn't have to be linker-script-related, it could be caused by your assembler code, or any of the commands you use to compile, assemble, and link your code.
Or, to put it like a computer would do: Insufficient input.
I agree it could by in other places, but if he has errors in het assembler code or in the code to compile or assemble at least one of his intermediate object files should be really big (circa 1mb).
Re:x64 gcc: kernel binary grows up to 1MB
Posted: Thu May 11, 2006 2:40 pm
by Solar
1) Who says it isn't?
2) I'm a bit fuzzy about all the possible permutations of [tt].org[/tt] and -Ttext, but I think I remember having had this "too-big" problem myself some day without ever touching the linker script.
Re:x64 gcc: kernel binary grows up to 1MB
Posted: Thu May 11, 2006 4:04 pm
by Candy
The "too-big" problem is that you insert a whole lot of space because you link something to binary implying a whole lot of space. He doesn't even use binary anywhere, he uses only ELF. That problem can't apply.
It can however be something similar. Does any object file being linked in stand out in size?
Re:x64 gcc: kernel binary grows up to 1MB
Posted: Thu May 11, 2006 4:38 pm
by paulbarker
From the gcc info pages:
`-fno-zero-initialized-in-bss'
If the target supports a BSS section, GCC by default puts
variables that are initialized to zero into BSS. This can save
space in the resulting code.
This option turns off this behavior because some programs
explicitly rely on variables going to the data section. E.g., so
that the resulting executable can find the beginning of that
section and/or make assumptions based on that.
The default is `-fzero-initialized-in-bss'.
You should be able to see whats going on now.
Re:x64 gcc: kernel binary grows up to 1MB
Posted: Fri May 12, 2006 8:00 am
by Guest
No, every object file has a normal size.
If i don't use `-fno-zero-initialized-in-bss' i still have same problem.
Re:x64 gcc: kernel binary grows up to 1MB
Posted: Fri May 12, 2006 8:04 am
by Solar
Please provide the command lines used in building (compiler, assembler, linker) as well as a quick list of any .org statements used in your ASM code, so we might be able to reproduce your problem.
I know I'm sounding like a technical helpdesk.
Re:x64 gcc: kernel binary grows up to 1MB
Posted: Fri May 12, 2006 5:17 pm
by Guest
To build the compiler and the linker i followed the instructions in the os faq (
http://www.osdev.org/osfaq2/index.php/G ... s-Compiler).
The error doesnt matter on the code.
I compiled:
Then i linked this code but the elf file was still 1MB.
I also tried to compile without the linker script, just
ld -o bla.elf main.o.
Now the file was OK (about 1.3kb).
Objdump gave me the following informations about the sections:
Code: Select all
test.elf: file format elf64-x86-64
Sections:
Idx Name Size VMA LMA File off Algn
0 .text 00000006 00000000004000e8 00000000004000e8 000000e8 2**2
CONTENTS, ALLOC, LOAD, READONLY, CODE
1 .eh_frame 00000038 00000000004000f0 00000000004000f0 000000f0 2**3
CONTENTS, ALLOC, LOAD, READONLY, DATA
2 .data 00000000 0000000000500128 0000000000500128 00000128 2**2
CONTENTS, ALLOC, LOAD, DATA
3 .bss 00000000 0000000000500128 0000000000500128 00000128 2**2
ALLOC
4 .comment 00000012 0000000000000000 0000000000000000 00000128 2**0
CONTENTS, READONLY
With the linker script i got (1MB file...):
Code: Select all
test.elf: file format elf64-x86-64
Sections:
Idx Name Size VMA LMA File off Algn
0 .text 00001000 0000000000200000 0000000000200000 00100000 2**2
CONTENTS, ALLOC, LOAD, READONLY, CODE
1 .data 00000000 0000000000201000 0000000000201000 00101000 2**2
CONTENTS, ALLOC, LOAD, DATA
2 .rodata 00000000 0000000000201000 0000000000201000 00102000 2**0
CONTENTS
3 .eh_frame 00000038 0000000000201000 0000000000201000 00101000 2**3
CONTENTS, ALLOC, LOAD, READONLY, DATA
4 .comment 00000fc8 0000000000201038 0000000000201038 00101038 2**0
CONTENTS, ALLOC, LOAD, READONLY, DATA
5 .bss 00000000 0000000000202000 0000000000202000 00102000 2**2
ALLOC
6 .note.GNU-stack 00000000 0000000000000000 0000000000000000 00102000 2**0
CONTENTS, READONLY
Notice that I linked .text to 0x200000 and the output file is still 1MB.
These informations might help.
Thanks in advance.
Re:x64 gcc: kernel binary grows up to 1MB
Posted: Sat May 13, 2006 4:13 am
by Guest
I played a bit with the starting addresses.
I found out that if i link the elf file to 1MB align addresses such
as 0x100000, 0x200000... the file will be 1MB
If i link the file to 0x200100 i get a 1.32kb output file.
Why ??
Re:x64 gcc: kernel binary grows up to 1MB
Posted: Fri May 19, 2006 3:09 am
by Pype.Clicker
that seriously looks like a bug in the binutils, if you ask me ... i'd check whether a newer version of binutils for x86-64 is available if i were you...
Re:x64 gcc: kernel binary grows up to 1MB
Posted: Fri May 19, 2006 4:56 am
by Solar
You "played a bit with the starting address", yet still you do not give sufficient information for us to reproduce the problem. (See my post from May 12th.)
If a toolchain behaves "illogical", then in 99% of all cases it is because you thought you did A, while actually you did B. Others can help you finding the problem, but only if you provide A and B.