使用“系统调用"的原因是什么?而不是直接调用函数? [英] What are the reasons to use "syscall" instead of calling the function directly?

问题描述

syscall 允许在Linux中进行间接系统调用.使用它的原因是什么-为什么它比直接调用该函数更好?

There's syscall which allows indirect system calls in Linux. What are the reasons to use it - and why is it better than direct call to the function?

推荐答案

有时内核会添加系统调用，而C库需要一段时间才能支持它们.

Sometimes the kernel adds system calls and it takes a while for the C library to support them.

或者也许您正在使用旧的Linux发行版进行编译，但希望在较新的Linux发行版上运行.

Or maybe you are compiling on an old Linux distribution, but want to run on a newer one.

示例代码:

// syscall 277 is sync_file_range() on x86_64 Linux.  The header
// files lack it on scc-suse10 where we compile, but the
// performance benefits are substantial, so we just call it
// directly.  FIXME someday.
#define SYNC_FILE_RANGE_WRITE 2
    syscall(277, fd, done, n, SYNC_FILE_RANGE_WRITE);

但是，通常，如果编译环境中的C库满足您的需要，则使用syscall没有任何优势. (一方面，它的可移植性比使用Linux特定的接口还要差，因为系统调用号因CPU而异.)

But in general, there is no advantage to using syscall if the C library in your compilation environment has what you need. (For one thing, it is even less portable than using a Linux-specific interface, since the system call numbers vary by CPU.)

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