assembly - GNU GAS 汇编中是否有代表当前地址的符号？

Question

我很想知道是否有任何特殊的 GAS 语法可以实现与 NASM 示例中相同的效果:

SECTION .data       

    msg:    db "Hello World",10,0  ; the 0-terminated string.
    len:    equ $-msg              ; "$" means current address.

特别是我对代表当前地址的符号 $ 感兴趣。

Answer 1

摘自 info as (GNU Binutils 2.21.90)，或在线查看 GAS 手册:https://sourceware.org/binutils/docs/as/Dot.html

5.4 The Special Dot Symbol

The special symbol . refers to the current address that as is assembling into. Thus, the expression melvin: .long . defines melvin to contain its own address.

Assigning a value to . is treated the same as a .org directive. Thus, the expression .=.+4 is the same as saying .space 4.

msg:    .ascii "Hello World!\n"       # not zero-terminated, use .asciz for that
msglen = . - msg                      # A .equ directive would be equivalent

这是相同 idiom used in NASM (len equ $ - symbol) 的 GAS 版本让汇编器为您计算某物的长度。