我感到困惑在FreeBSD 9.0/amd64上也是如此。 (我使用NASM的彙編),我所做的是:
$ cat foo.asm
global _start
_start:
mov rax, 4 ; write
mov rdi, 1 ; stdout
mov rsi, rsp ; address
mov rdx, 16 ; 16bytes
syscall
mov rax, 1 ; exit
syscall
$ nasm -f elf64 foo.asm && ld -o foo foo.o
$ ./foo | hd
00000000 00 00 00 00 00 00 00 00 01 00 00 00 00 00 00 00 |................|
00000010
$ ./foo 2 | hd
00000000 02 00 00 00 00 00 00 00 b8 dc ff ff ff 7f 00 00 |................|
00000010
$ ./foo 2 3 | hd
00000000 00 00 00 00 00 00 00 00 03 00 00 00 00 00 00 00 |................|
00000010
$ ./foo 2 3 4 | hd
00000000 00 00 00 00 00 00 00 00 04 00 00 00 00 00 00 00 |................|
00000010
$ ./foo 2 3 4 5 | hd
00000000 05 00 00 00 00 00 00 00 b0 dc ff ff ff 7f 00 00 |................|
00000010
我預期的argc在RSP,但事實並非如此。
我猜想內核(圖像激活器)設置寄存器。我搜索了源代碼樹,在/usr/src/sys/amd64/amd64/machdep.c(exec_setregs)中找到了以下代碼。
regs->tf_rsp = ((stack - 8) & ~0xFul) + 8;
regs->tf_rdi = stack; /* argv */
這些行看起來是說rsp是對齊的,實際數據是rdi。我改變了我的代碼,並獲得了預期的結果。
$ cat foo.asm
global _start
_start:
push rdi
mov rax, 4 ; write
mov rdi, 1 ; stdout
pop rsi
mov rdx, 16 ; 16bytes
syscall
mov rax, 1 ; exit
syscall
$ nasm -f elf64 foo.asm && ld -o foo foo.o
$ ./foo | hd
00000000 01 00 00 00 00 00 00 00 b0 dc ff ff ff 7f 00 00 |................|
00000010
$ ./foo 2 | hd
00000000 02 00 00 00 00 00 00 00 a8 dc ff ff ff 7f 00 00 |................|
00000010
$ ./foo 2 3 | hd
00000000 03 00 00 00 00 00 00 00 a8 dc ff ff ff 7f 00 00 |................|
00000010
$ ./foo 2 3 4 | hd
00000000 04 00 00 00 00 00 00 00 a8 dc ff ff ff 7f 00 00 |................|
00000010
$ ./foo 2 3 4 5 | hd
00000000 05 00 00 00 00 00 00 00 a8 dc ff ff ff 7f 00 00 |................|
00000010
你可以試試偏下?
嘗試在調試器中運行它以查看堆棧佈局是否符合您的期望。 – user786653
謝謝,我已經有一段時間了,通常8(%esp)有argc,但有時候不會,我想我會繼續努力吧! :) – timmmay