linux程序集“collect2：ld返回1退出状态”

Question

I entered the source code on a web site of online coding.

But I got error below the source code.

I think I omitted "main".

Since I learned Intel assmbly, I don't know how to fix it.

Could you help me?

Thank you for helping me in advance.

SECTION .DATA
    hello:     db 'Hello world!',10
    helloLen:  equ $-hello

SECTION .TEXT
    GLOBAL _START

_START:


; Write 'Hello world!' to the screen
mov eax,4            ; 'write' system call
mov ebx,1            ; file descriptor 1 = screen
mov ecx,hello        ; string to write
mov edx,helloLen     ; length of string to write
int 80h              ; call the kernel

; Terminate program
mov eax,1            ; 'exit' system call
mov ebx,0            ; exit with error code 0
int 80h              ; call the kernel

/usr/lib/gcc/i686-linux-gnu/4.6/../../../i386-linux-gnu/crt1.o: In function _start': (.text+0x18): undefined reference to main' collect2: ld returned 1 exit status

Answer 1

If you are just using GCC as a linker and don't care about the C runtime then you can exclude it (as Jester pointed out) by passing -nostdlib to gcc . You then need to provide a _start symbol so the code would look like:

SECTION .DATA
    hello:     db 'Hello world!',10
    helloLen:  equ $-hello

SECTION .TEXT
    GLOBAL _start

_start:
; Write 'Hello world!' to the screen
    mov eax,4            ; 'write' system call
    mov ebx,1            ; file descriptor 1 = screen
    mov ecx,hello        ; string to write
    mov edx,helloLen     ; length of string to write
    int 80h              ; call the kernel

    ; Terminate program
    mov eax,1            ; 'exit' system call
    mov ebx,0            ; exit with error code 0
    int 80h              ; call the kernel

You'd assemble and link it like this:

nasm -f elf file.asm
gcc -m32 -nostdlib -o file file.o

Alternatively you can link directly with ld so you could also do this:

nasm -f elf file.asm
ld -melf_i386 -o file file.o

This would generate a 32-bit Linux executable called file

Using C Library/runtime

Although I don't think the following is what you intended, someone may find the following information useful:

You can use GCC and have the C library available to your assembly code by renaming _START to main . The C runtime contains an entry point called _start that handles initialization and then calls a function called main . You can take advantage of the C library but main has to setup the stack frame correctly and properly clean it up and return when finished since main will be treated as a C function. The code would look something like this:

EXTERN printf    ; Tell the assembler printf is provided outside our file

SECTION .DATA
    hello:     db 'Hello world!',10,0 ; Null terminate for printf
    helloLen:  equ $-hello-1          ; Exclude null by reducing len by 1

SECTION .TEXT
    GLOBAL main

; main is now a C function
main:
    push ebp              ; Setup stack frame
    mov  ebp, esp
    push ebx              ; We need to preserve EBX (C Calling convention)

    ; Write 'Hello world!' to the screen
    mov eax,4            ; 'write' system call
    mov ebx,1            ; file descriptor 1 = screen
    mov ecx,hello        ; string to write
    mov edx,helloLen     ; length of string to write
    int 80h              ; call the kernel

    ; Write 'Hello World!' with C printf
    push hello           ; push the address of string to print
    call printf          ; call printf in C library
    add esp, 4           ; Restore stack pointer
                         ; push hello pushed 4 bytes on stack

    mov  eax, 0x0        ; Return value of 0
    pop  ebx             ; Restore EBX
    leave
    ret                  ; Return to C runtime which will cleanup and exit

This example uses both int 0x80 system call to write standard output, and uses C printf to do the same. You can assemble and link to an executable called file with:

nasm -f elf file.asm
gcc -m32 -o file file.o