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

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

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?

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1 に答える 1

18

単純型を返す関数の場合:

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

残りはスタックに置かれます。

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

もちろん、ここでの「引数」は 4 バイト オブジェクトを意味します。引数が 4 バイトを超える場合、分割されます。

-[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

返された値 (最大 16 バイト) は、r0、r1、r2、r3 に配置されます。

構造体を返す関数の場合:r0戻り値のポインターを格納するために使用されます。

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
于 2010-03-14T13:45:33.190 に答える