32位指针与X86-64赛：为什么不呢？ [英] 32-bit pointers with the x86-64 ISA: why not?

问题描述

在X86-64指令集增加了更多的寄存器和其他方面的改进，以帮助简化执行code。然而，在许多应用中增加的指针的大小是一种负担。在每一个指针额外的，未使用的字节阻塞缓存，甚至可能溢出内存。 GCC，例如，建立与 -m32 标记，而我认为这是什么原因。

The x86-64 instruction set adds more registers and other improvements to help streamline executable code. However, in many applications the increased pointer size is a burden. The extra, unused bytes in every pointer clog up the cache and might even overflow RAM. GCC, for example, builds with the -m32 flag, and I assume this is the reason.

这是可能加载一个32位的值，并把它作为一个指针。这并不需要额外的指令，只需加载/计算的32位，从结果地址加载。诀窍将无法移植，但是，作为平台有不同的内存映射。在Mac OS X中，地址空间的整个低4吉布被保留。然而，对于一个程序我写的，hackishly加入 0x100000000L 32位的地址之前使用经过改进的性能大大超过真正的64位地址，或编译 -m32 。

It's possible to load a 32-bit value and treat it as a pointer. This doesn't necessitate extra instructions, just load/compute the 32 bits and load from the resulting address. The trick won't be portable, though, as platforms have different memory maps. On Mac OS X, the entire low 4 GiB of address space is reserved. Still, for one program I wrote, hackishly adding 0x100000000L to 32-bit "addresses" before use improved performance greatly over true 64-bit addresses, or compiling with -m32.

有没有什么根本性的障碍，有32位，X86-64平台？我想，支持这种幻想会增加复杂性，任何操作系统，任何人想要去年20％应该只是让它工作™，但它似乎仍然认为这将是各种计算密集型程序的最佳选择。

Is there any fundamental impediment to having a 32-bit, x86-64 platform? I suppose that supporting such a chimera would add complexity to any operating system, and anyone wanting that last 20% should just Make it Work™, but it still seems that this would be the best fit for a variety of computationally intensive programs.

推荐答案

有一个ABI称为X32为Linux的发展。这是和x86_64 IA32类似之间的搭配，你的描述 - 在使用完整的64位寄存器组32位的地址空间。它需要一个定制的内核，binutils的和GCC。

There is an ABI called "x32" for linux in development. It's a mix between x86_64 and ia32 similar to what you describe - 32 bit address space while using the full 64 bit register set. It needs a custom kernel, binutils and gcc.

有些SPEC运行表明约30％，在一些基准测试一个服务表现的改善。参见更多信息在 https://sites.google.com/site/x32abi/

Some SPEC runs indicate a performace improvement of about 30% in some benchmarks. See further information at https://sites.google.com/site/x32abi/

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