问题
We use Linux system calls like fork(), pthread(), signal() and so on in C or C++ programs and compile the program to generate executable file (a.out). Now my doubt is whether the file a.out contain the object code of all linux system calls used, or whether the executable contain only the calls to system functions and the system call functions are linked during runtime? Suppose if I move my a.out file to some other Linux operating system which implements system calls in different syntax and try to compile it there will it work?
My doubt is whether system call function definitions part of a.out file?
回答1:
User space binaries don't contain implementations of system calls. That would mean that any user could inject any code into kernel and take over system.
Instead they need to switch to kernel mode, by using processor interrupt or special instruction. Then processor can execute system call implementation from the kernel.
User space library, such as libc, is usually used, which provides stubs, which convert arguments of a syscall to a proper protocol and trigger jump to kernel mode. It is usually linked dynamically, so these stubs also don't appear in executable file.
来源：https://stackoverflow.com/questions/31367477/does-executable-file-of-c-program-contain-object-code-of-system-calls-also