SYSCALL_MODULE(9)

💖 SYSCALL_MODULE(9) 💖

okay bestie, gather round, because this is a Kernel Developer's Manual page and it's about the SYSCALL_MODULE macro — yes, the one that lets you declare a whole new syscall from inside a kernel module. main character energy fr fr 👑

✨ NAME ✨

SYSCALL_MODULE — the syscall kernel module declaration macro. that's it, that's the vibe 🎀

🌸 SYNOPSIS 🌸

#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/proc.h>
#include <sys/module.h>
#include <sys/sysent.h>

SYSCALL_MODULE(name, int *offset, struct sysent *new_sysent,
    modeventhand_t evh, void *arg);

🦋 DESCRIPTION 🦋

so like. the SYSCALL_MODULE() macro declares a new syscall. that's the whole job. and when it expands, it gives you a kernel module declaration named sys/name. cute, right? ✨

here's the rest of the arguments this macro expects, no gatekeeping:

• offset — a pointer to an int that saves the offset in struct sysent where the syscall gets allocated. now listen: if the location that offset points to holds a non 0 number, that number will be used if possible. but if it holds 0, then a number will be assigned for you. lowkey generous 💅
• new_sysent — a pointer to a structure that specifies the function implementing the syscall, plus how many arguments that function needs (peep <sys/sysent.h> for that).
• evh — a pointer to the kernel module event handler function, and it takes arg as its argument. go read module(9) if you want the full tea 🫖
• arg — the argument that gets passed to the callback functions of the evh event handler whenever it's called.

and here's a little bonus fact for you: the syscall number assigned to the module can be retrieved using the modstat(3) and modfind(3) library functions over in libc. also the MACRO SYSCALL_MODULE_HELPER() includes SYSCALL_MODULE() plus a whole bunch of its boilerplate code, so you don't have to hand-write all that 😭 obsessed

🌈 EXAMPLES 🌈

if you want a minimal example of a syscall module, it's literally sitting right here:

/usr/share/examples/kld/syscall/module/syscall.c

go look at it, bestie, it's giving tutorial ✨

💜 SEE ALSO 💜

• module(9)
• /usr/share/examples/kld/syscall/module/syscall.c

👑 AUTHORS 👑

this manual page was written by Alexander Langer <alex@FreeBSD.org>. iconic behavior, we stan 💖

ok that's the whole page, no cap, nothing skipped 💅

so this page came to you from the Debian edition of the manual, dated January 24, 2015, and it's filed under SYSCALL_MODULE(9). mwah, go write a syscall 🎀✨🦋