I am trying to learn writing assembly language for 64 bit Mac OS. I have no problem with 32 bit Mac OS and both 32 bit and 64 bit Linux.
我正在努力学习为64位Mac OS编写汇编语言。我对32位Mac OS以及32位和64位Linux没有任何问题。
However, Mac OS 64 bit is different and I couldn't figure out. Therefore I am here to ask for help.
但是，Mac OS 64位是不同的，我无法弄清楚。因此，我在这里寻求帮助。
I have not problem using system call to print. However, I would like to learn how to call C functions using 64 bit assembly language of Mac OS.
我没有使用系统调用打印的问题。但是，我想学习如何使用Mac OS的64位汇编语言调用C函数。
Please look at the following code
请查看以下代码
.data
_hello:
.asciz "Hello, world\n"
.text
.globl _main
_main:
movq $0, %rax
movq _hello(%rip), %rdi
call _printf
I use $ gcc -arch x86_64 hello.s
我使用$ gcc -arch x86_64 hello.s
to assemble and link.
组装和链接。
It generates binary code. However, I got a segmentation fault when running it.
它生成二进制代码。但是，运行它时出现了分段错误。
I tried adding "subq $8, %rsp" before calling _printf, still the same result as before.
我在调用_printf之前尝试添加“subq $ 8，％rsp”，仍然和以前一样。
What did I do wrong?
我做错了什么？
By the way, is that any way to debug this code on Mac? I tried adding -ggdb or -gstab or -gDWARF, and $gdb ./a.out, and can't see the code and set break points.
顺便说一下，这是在Mac上调试此代码的方法吗？我尝试添加-ggdb或-gstab或-gDWARF和$ gdb ./a.out，但无法查看代码并设置断点。
1 个解决方案
#1
8
You didn't say exactly what the problem you're seeing is, but I'm guessing that you're crashing at the point of the call to printf. This is because OS X (both 32- and 64-bit) requires that the stack pointer have 16-byte alignment at the point of any external function call.
你没有确切地说出你所看到的问题是什么，但我猜你在调用printf时崩溃了。这是因为OS X（32位和64位）要求堆栈指针在任何外部函数调用时具有16字节对齐。
The stack pointer was 16-byte aligned when _main was called; that call pushed an eight-byte return address onto the stack, so the stack is not 16-byte aligned at the point of the call to _printf. Subtract eight from %rsp before making the call in order to properly align it.
调用_main时，堆栈指针是16字节对齐的;该调用将一个8字节的返回地址压入堆栈，因此堆栈在调用_printf时不是16字节对齐的。在进行调用之前从％rsp中减去8，以便正确对齐它。
So I went ahead and debugged this for you (no magic involved, just use gdb, break main, display/5i $pc, stepi, etc). The other problem you're having is here:
所以我继续为你调试这个（没有魔法，只需使用gdb，break main，display / 5i $ pc，stepi等）。你遇到的另一个问题是：
movq _hello(%rip), %rdi
This loads the first eight bytes of your string into %rdi, which isn't what you want at all (in particular, the first eight bytes of your string are exceedingly unlikely to constitute a valid pointer to a format string, which results in a crash in printf). Instead, you want to load the address of the string. A debugged version of your program is:
这会将字符串的前八个字节加载到％rdi中，这根本不是您想要的（特别是，字符串的前八个字节极不可能构成指向格式字符串的有效指针，这会导致在printf崩溃）。相反，您想要加载字符串的地址。调试版程序是：
.cstring
_hello: .asciz "Hello, world\n"
.text
.globl _main
_main:
sub $8, %rsp // align rsp to 16B boundary
mov $0, %rax
lea _hello(%rip), %rdi // load address of format string
call _printf // call printf
add $8, %rsp // restore rsp
ret
#1
8
You didn't say exactly what the problem you're seeing is, but I'm guessing that you're crashing at the point of the call to printf. This is because OS X (both 32- and 64-bit) requires that the stack pointer have 16-byte alignment at the point of any external function call.
你没有确切地说出你所看到的问题是什么，但我猜你在调用printf时崩溃了。这是因为OS X（32位和64位）要求堆栈指针在任何外部函数调用时具有16字节对齐。
The stack pointer was 16-byte aligned when _main was called; that call pushed an eight-byte return address onto the stack, so the stack is not 16-byte aligned at the point of the call to _printf. Subtract eight from %rsp before making the call in order to properly align it.
调用_main时，堆栈指针是16字节对齐的;该调用将一个8字节的返回地址压入堆栈，因此堆栈在调用_printf时不是16字节对齐的。在进行调用之前从％rsp中减去8，以便正确对齐它。
So I went ahead and debugged this for you (no magic involved, just use gdb, break main, display/5i $pc, stepi, etc). The other problem you're having is here:
所以我继续为你调试这个（没有魔法，只需使用gdb，break main，display / 5i $ pc，stepi等）。你遇到的另一个问题是：
movq _hello(%rip), %rdi
This loads the first eight bytes of your string into %rdi, which isn't what you want at all (in particular, the first eight bytes of your string are exceedingly unlikely to constitute a valid pointer to a format string, which results in a crash in printf). Instead, you want to load the address of the string. A debugged version of your program is:
这会将字符串的前八个字节加载到％rdi中，这根本不是您想要的（特别是，字符串的前八个字节极不可能构成指向格式字符串的有效指针，这会导致在printf崩溃）。相反，您想要加载字符串的地址。调试版程序是：
.cstring
_hello: .asciz "Hello, world\n"
.text
.globl _main
_main:
sub $8, %rsp // align rsp to 16B boundary
mov $0, %rax
lea _hello(%rip), %rdi // load address of format string
call _printf // call printf
add $8, %rsp // restore rsp
ret