This is what the System V ABI specifies:

R_X86_64_64 | S + A (ie Symbol value + Addend)

I assembled this shared object and PIE executable:

; PIE executable

        global _start
        extern msg

        section .text

_start:
        mov rdi, 1      ; stdout fd
        mov rsi, msg
        mov rdx, 9      ; 8 chars + newline
        mov rax, 1      ; write syscall
        syscall

        xor rdi, rdi    ; return code 0
        mov rax, 60     ; exit syscall
        syscall

; shared object
        global msg:data msg.end-msg
        section .data

msg: db "hi there", 10
 .end:

When performing readelf on the PIE executable, in the .rela.dyn I get these relocation entries:

000000001007  000100000001 R_X86_64_64       0000000000003000 msg + 0
000000003000  000100000005 R_X86_64_COPY     0000000000003000 msg + 00

As I understand it:

1. R_X86_64_64 performs the relocation inside the .text section – it changes the operand (which is located at offset 0x1007 in mem) to the value of the specified symbol (in this case, 0x3000)
2. R_X86_64_COPY tells the dynamic linker to look for the dynamic symbol in the shared object, and then copy the value of the dynamic symbol to address specified by the symbol (in this case 0x3000) + the base address the object was loaded at

Now if I apply the R_X86_64_64 relocation the way the ABI specified, I will just get 0x3000 as msg‘s address which is obviously incorrect! Shouldn’t I add load base address here too?

Is there something I’m missing?

Thanks in advance