assembly - relocation truncated to fit r_386_8 against .bss'

Question

When i type ld -m elf_i386 -o loop loop.asm, i get the error stated in the title, any idea what causes it? Sorry if the code looks bad, fairly new to assembly.

cr equ 13 
lf equ 10 

section .bss
numA resb 1

section .text

global _start:

mov [numA],byte 0
call loop1
jmp endend
loop1:
xor cx,cx
mov al, $numA
cmp cx, 0x0A
jle else 
inc al
jmp end
else:
dec al
jmp end
end:
mov [$numA], al
inc cx
cmp cx,20
jle loop1

endend:
mov dl,$numA
mov ah,2
int 21h

Answer 1

In NASM, $numA is the same as numA. A leading $ stops the assembler from considering it as a register name. Thus you can write mov eax, [$eax] to load the eax register from a symbol called eax. (So you could link with C which used int eax = 123;)

So mov [$numA], al looks weird, but it's really just mov [numA], al and isn't the source of the error.

---

You're getting the error from mov dl,$numA which does a mov dl, imm8 of the low byte of the address.

The linker warns you because the address of numA doesn't fit in 1 byte, so the r_386_8 relocation would have had to truncate the address.

The _8 tells you it's a relocation that asks the linker to fill in 8 bits (1 byte) as an absolute address. (8-bit relative branch displacements have a different relocation type, although normally you'd use a 32-bit displacement for jumping to a symbol in another file.)

The r_386 tells you it's an i386 relocation as opposed to some type of r_x86_64 relocation (which could be absolute or RIP-relative), or a MIPS jump-target relocation (which would need to right-shift the offset by 2). Possibly related: Relocations in the System V gABI (generic ABI, for which the i386 SysV psABI is a "processor supplement").