CODEWITHSUNDEEP
assemblyrustlinkerldinstructions
罗旭皓
罗旭皓

Reputation: 91

How to properly link two object files without affecting rip relative addressing?

I have two object files, one is generated from assembly and another is compiled from rust. From the assembly I call a function in the rust (as below) so I need to link them together.

//boot.asm
section .text
...
extern _start
call _start
...

//main.rs
#![no_std]
#![no_main]

#[no_mangle]
pub extern fn _start() {
    let hello = b"hello_world!";
    ...
}

After compile I found there are a .rodata section and a .text section in the rust object file, and there are instructions that use rip-relative addressing to address the "hello world" string in the .rodata section:

//section .text
...
  let hello = b"hello world!";
2017e7: 48 8d 05 2e ea ff ff    lea    -0x15d2(%rip),%rax
2017ee: 48 89 44 24 30          mov    %rax,0x30(%rsp)
...

I also have .rodata section and .text section in the assembly. However, during linking the linker just merge the two .rodata sections and two .text sections into one .rodata section and one .text section, which affects the rip-relative addressing, causing my program not working working. Can anybody tell me how should I make modifications to resolve the problem? This is my linker script, Should I modify it?

ENTRY(start)

SECTIONS {
    . = 0x00100000;

    .boot :
    {
        *(.multiboot_header)
    }

    .text :
    {
        *(.text)
    }
}

Thank you for your help!

Upvotes: 3

Views: 973

Answers (1)

罗旭皓
罗旭皓

Reputation: 91

I figure it out. Thanks to the hints offered by Peter Cordes. The reason is that I compiled my rust code to an executable rather than a library. I should compile it into a library(a .a file) so the linker can calculate the offset of rip-relative addressing during link-time. If it's compiled into an executable then the offset is already calculated so the linker can't recalculate it and the problem I mentioned will arouse. Please forgive me that this is a silly mistake(how could you link an executable with other), I haven't look into such things seriously before.

Upvotes: 4

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