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.

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.

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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").