关于目标C调用约定和参数传递的ARM问题 [英] Question about Objective C calling convention and argument passing on ARM

问题描述

我想知道如何客观C运行时处理的参数，当我打电话像

I want to know how objective C runtime handle arguments when I call a objective C method like

[NSString stringWithFomat:@"%@, %@", @"Hello", @"World"]

有三个参数为这一目标调用C，它是如何相比，ARM系统上典型的方式工作。我所知道的寄存器R0，R1，R2，R3将举行第4个参数，如何有额外的参数？它是如何把它们在堆栈上，后来弹出他们？

There are three arguments for this objective C call, how does it work compared to typical way on a ARM system. I have known register r0, r1, r2, r3 will hold first 4 arguments, how about there are additional arguments? How does it put them on a stack and pop them later?

推荐答案

有关函数返回一个简单类型：

For functions that returns a simple type:

r0 = self (NSString)
r1 = _cmd (@selector(stringWithFormat:))
r2 = 1st argument (@"%@, %@")
r3 = 2nd argument (@"Hello")

那么剩下的放在栈上：

then the rest is placed on the stack:

[sp,#0] = 3rd argument (@"World")
[sp,#4] = 4th argument (does not exist in your example)
...

当然，说法在这里是指一个4字节的对象。如果参数有> 4个字节那么它将被拆分出来，例如

Of course, "argument" here means a 4-byte object. If the argument has >4 bytes then it will be split out, e.g.

-[UIView initWithFrame:rect];

r0 = self
r1 = _cmd
r2 = rect.origin.x
r3 = rect.origin.y
[sp,#0] = rect.size.width
[sp,#4] = rect.size.height

返回值（高达16字节）将被放置在R0，R1，R2，R3

The returned value (up to 16 bytes) will be placed in r0, r1, r2, r3.

对于返回结构功能： R0 是用来存储返回值的指针

For functions that returns a struct: r0 is used to store the pointer of the return value.

NSRange retval = [self rangeOfString:string options:options range:range]

r0 = &retval (of type NSRange*)
r1 = self
r2 = _cmd (@selector(rangeOfString:options:range:))
r3 = string
[sp,#0] = options
[sp,#4] = range.location
[sp,#8] = range.length

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