AT&T语法和Intel语法x86汇编的区别

AT&T语法和Intel语法x86汇编的区别<转自 北风北的猪>

x86汇编一直存在两种不同的语法，intel语法和AT&T语法，在intel的官方文档中使用intel语法，Windows也使用intel语法，而UNIX平台的汇编器一直使用AT&T语法。 linux下，x86汇编AT&T语法用GAS编译，Intel语法用NASM编译。 AT&T和Intel语法没有好坏之分，只是语法有差异而已。 GAS的语法主要有： * 寄存器名前缀% * 操作数是源在前，目的在后。与Intel语法刚好相反。 * 操作数长度在指令名后缀，b表示8位，w表示16位，l表示32位，如movl %ebx,%eax。 * 立即操作数（常量）用$标示，如addl $5,%eax * 变量加不加$有区别。如movl $foo, %eax表示把foo变量地址放入寄存器%eax。movl foo,%eax表示把foo变量值放入寄存器%eax。 hello_world例子 NASM (hello.asm) section .text ;section declaration ;we must export the entry point to the ELF linker or global _start ;loader. They conventionally recognize _start as their ;entry point. Use ld -e foo to override the default. _start: ;write our string to stdout mov edx,len ;third argument: message length mov ecx,msg ;second argument: pointer to message to write mov ebx,1 ;first argument: file handle (stdout) mov eax,4 ;system call number (sys_write) int 0x80 ;call kernel ;and exit mov ebx,0 ;first syscall argument: exit code mov eax,1 ;system call number (sys_exit) int 0x80 ;call kernel section .data ;section declaration msg db "Hello, world!",0xa ;our dear string len equ $ - msg ;length of our dear string GAS (hello.S) .text # section declaration # we must export the entry point to the ELF linker or .global _start # loader. They conventionally recognize _start as their # entry point. Use ld -e foo to override the default. _start: # write our string to stdout movl $len,%edx # third argument: message length movl $msg,%ecx # second argument: pointer to message to write movl $1,%ebx # first argument: file handle (stdout) movl $4,%eax # system call number (sys_write) int $0x80 # call kernel # and exit movl $0,%ebx # first argument: exit code movl $1,%eax # system call number (sys_exit) int $0x80 # call kernel .data # section declaration msg: .ascii "Hello, world!\n" # our dear string len = . - msg # length of our dear string Fornasmexample: $ nasm -f elf hello.asm Forgasexample: $ as -o hello.o hello.S This makeshello.oobject file. Second step is producing executable file itself from the object file by invoking linker: $ ld -s -o hello hello.o 看一些例子： +-----------------------------------+---------------------------------------------+ |          Intel Code                         |         AT&T Code                                     | +-----------------------------------+---------------------------------------------+ | mov      eax,1                              | movl     $1,%eax                                     | | mov      ebx,0ffh                         | movl     $0xff,%ebx                                | | int         80h                                | int         $0x80                                        | | mov      ebx, eax                          | movl     %eax, %ebx                                | | mov      eax,[ecx]                         | movl     (%ecx),%eax                              | | mov      eax,[ebx+3]            | movl     3(%ebx),%eax                             | | mov      eax,[ebx+20h]               | movl     0x20(%ebx),%eax                    | | add       eax,[ebx+ecx*2h]           | addl      (%ebx,%ecx,0x2),%eax            | | lea        eax,[ebx+ecx]                | leal       (%ebx,%ecx),%eax                  | | sub       eax,[ebx+ecx*4h-20h]    | subl      -0x20(%ebx,%ecx,0x4),%eax | +-----------------------------------+----------------------------------------------+ cmp eax,ebx ---- cmpl %ebx,%eax 参考： Linux Assembly HOWTO,3.2. GAS,   6.2. Hello, world!    GCC-Inline-Assembly-HOWTO,3. GCC Assembler Syntax.    这个gnu的as manual有更详细的说明，还有针对不同硬件的： Using as,   9.13 80386 Dependent Features