我该怎么做就IPhone内联汇编？ [英] How do I do inline assembly on the IPhone?

问题描述

它是如何做的？哪些步骤，我需要采取和什么是陷阱，陷阱有没有考虑？

How is it done? What steps do I need to take and what pitfalls and gotchas are there to consider?

推荐答案

我已经得到这个工作，由于一些内部帮助过的苹果Devforums ，如果​​你是一个专门的IPhone开发商应该注册。

I've gotten this to work, thanks to some inside help over at the Apple Devforums, you should sign up if you're a dedicated IPhone developer.

第一件事，第一，它的 __ __ ASM（）的，不是纯的 ASM（）的

First thing's first, it's __asm__(), not plain asm().

其次，在默认情况下，X code生成编译针对ARM Thumb指令集内联汇编编译目标，所以的 USAT 的无法识别为一个正确的指令。为了解决这个问题，做目标获取信息。向下滚动到节GCC 4.0 - code一代，取消选择编译为Thumb。然后，如果你活动的SDK设置为设备

Secondly, by default, XCode generates a compilation target that compiles inline assembly against the ARM Thumb instruction set, so usat wasn't recognized as a proper instruction. To fix this, do "Get Info" on the Target. Scroll down to the section "GCC 4.0 - Code Generation" and uncheck "Compile for Thumb". Then this following snippet will compile just fine if you set the Active SDK to "Device"

inline int asm_saturate_to_255 (int a) {
  int y;
  __asm__("usat %0, #8, %1\n\t" : "=r"(y) : "r"(a));
  return y;
}

当然，现在也不会与IPhone模拟器的工作。但是的 TargetConditionals.h 的有你定义支持#ifdef反对。即* TARGET_OS_IPHONE *和* TARGET_IPHONE_SIMULATOR *。

Naturally, now it won't work with the IPhone Simulator. But TargetConditionals.h has defines you can #ifdef against. Namely *TARGET_OS_IPHONE* and *TARGET_IPHONE_SIMULATOR*.

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