问题描述
关于以下小代码，这在另一篇文章中进行了说明，有关结构的大小以及正确对齐数据的所有可能性:
Concerning the following small code, which was illustrated in another post about the size of structure and all the possibilities to align data correctly :
struct
{
char Data1;
short Data2;
int Data3;
char Data4;
} x;
unsigned fun ( void )
{
x.Data1=1;
x.Data2=2;
x.Data3=3;
x.Data4=4;
return(sizeof(x));
}
我得到了相应的反汇编(64位)
I get the corresponding disassembly (with 64 bits)
0000000000000000 <fun>:
0: 55 push %rbp
1: 48 89 e5 mov %rsp,%rbp
4: c6 05 00 00 00 00 01 movb $0x1,0x0(%rip) # b <fun+0xb>
b: 66 c7 05 00 00 00 00 movw $0x2,0x0(%rip) # 14 <fun+0x14>
12: 02 00
14: c7 05 00 00 00 00 03 movl $0x3,0x0(%rip) # 1e <fun+0x1e>
1b: 00 00 00
1e: c6 05 00 00 00 00 04 movb $0x4,0x0(%rip) # 25 <fun+0x25>
25: b8 0c 00 00 00 mov $0xc,%eax
2a: 5d pop %rbp
2b: c3 retq
我不知道如何计算位于右侧的术语，似乎是所使用的address of local variables.而且，我不知道用%rip register
I don't know how to calculate the terms located on the right which seems to be the address of local variables used. Moreover, I don't know to calculate it with %rip register
您能否举一个显示%rip与%rsp或%rbp之间的链接的示例，即特别是在使用move指令时在地址的计算中.
Could you give an example which shows the link between %rip and %rsp or %rbp, i.e especially in the computation of address when I use move instructions.
推荐答案
RIP寻址始终相对于RIP(64位指令指针)寄存器.因此它只能用于全局变量. 0偏移量等于RIP寻址指令之后的下一条指令的地址.例如:
RIP addressing is always relative to RIP (64bit Instruction Pointer) register. So it can be use for global variables only. The 0 offset is equal to address of the following instruction after the RIP-addressed instruction. For example:
mov al,[rip+2] al=53
jmp short next (length=2 bytes)
db 53
next:
mov bl,[rip-7] (length=6 bytes) bl=53
通常不会直接在代码中混入数据，除非立即添加，但这表明如果您实际运行偏移很小的代码会发生什么情况.
You wouldn't normally mix data right in with your code, except as an immediate, but this shows what would happen if you actually ran code with very small offsets.
在代码中，您无法查看和检查偏移量(看到四个零)，因为您已分解了.o.拆卸时，使用objdump -drwC显示符号名称/重定位.当您将此对象链接到可执行文件时，它们将由链接器填充.
In your code you cannot see and check offsets (you see four zeros) because you disassembled a .o. Use objdump -drwC to show symbol names / relocations when disassembling. They will be filled by the linker when you link this object into an executable.
访问相对于`rbp的本地人的示例:
Example for accessing locals relative to `rbp:
push rbp ;save rbp
mov rbp,rsp ;rbp = pointer to return address (8 bytes)
sub rsp,64 ;reserve 64 bytes for local variables
mov rax,[rbp+8]; rax = the last stack-passed qword parameter (if any)
mov rdx,[rbp]; rdx = return address
mov rcx,[rbp-8]; rcx = first qword local variable (this is undefined now)
mov r8, [rbp-16]; r8 = second qword local variable (this is undefined now)
.
.
mov rsp,rbp
pop rbp
ret
这篇关于了解intel汇编中的％rip注册的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！