Linux kernel 3.4的X32 ABI介绍

New X32 ABI: 64-bit mode with 32-bit pointers

The 64 bits mode of x86 CPUs enlarges the CPU registers to 64 bit, allowing to address larger (>4GB) amounts of memory. This widening, however, has a drawback. Because memory addresses are 64-bit wide, pointers occupy 64 bits of space, the double of space used in 32 bits mode, so binaries compiled for the 64-bit mode are bigger, and when these programs run they use more RAM. And since they are bigger they can cause a performance loss, because with bigger memory addresses, less CPU instructions will fit in the CPU caches.

Some programs have workloads CPU and pointer intensive enough to care about this performance, but with memory requirements not big enough to care about 64-bit memory addressing. They can avoid the 64-bit pointer overhead by just using the 32 bits mode: Processors still allow to run 32-bit operative systems, or run 32-bit programs on top of 64-bit kernels. But this choice also has problems. When a program runs in 32-bit mode, it loses all the other features of the 64-bit mode: larger number of CPU registers, better floating-point performance, faster PIC (position-independent code) shared libraries, function parameters passed via registers, faster syscall instruction...

So a new X32 kernel ABI has been created. A program compiled for this new ABI can run in the 64-bit mode, with all its features, but it uses 32 bits pointers and 32-bit long C type. So applications who need it can enjoy the performance of the 64-bit mode, but with the memory requirements of a 32 bits ABI. Code: (commit)

Recommended LWN article: The x32 system call ABI

Slides from the developers: link

Official X32 coordination site: http://sites.google.com/site/x32abi