How to call kernel code in libc ? (windows or linux)

Question

I mean, how the kernel expose its function to user land application.

Answer 1

Kernel functions are called using syscalls, which usually take form of filling some registers (type of syscall, parameters, ...) and doing a software interrupt (int 0x80) or sysenter instruction (if your architecture supports it).

If you're doing this on Linux, you might want to see some Linux syscall documentation, like one here: http://bluemaster.iu.hio.no/edu/dark/lin-asm/syscalls.html

There surely exists some similar documentation for other kernels (windows').

Answer 2

Assuming you are talking about Linux, you put your arguments in registers and call interrupt 0x80. The name for this is "system call" See these links:

• http://www.ibm.com/developerworks/linux/library/l-system-calls/
• http://www.linuxjournal.com/article/4048

Windows is probably similar, this looks like a good article:

http://www.codeguru.com/cpp/w-p/system/devicedriverdevelopment/article.php/c8035

etc... google