SYSCALL(2)

💅 SYSCALL(2) — the indirect system call page, bestie edition

okay so this is the syscall(2) page from the System Calls Manual, and honestly? it's a little icon. let's get into it 🫶

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✨ NAME ✨

syscall, __syscall — indirect system call

like, you're calling a syscall indirectly, iykyk 💫

📚 LIBRARY 📚

Standard C Library (libc, -lc)

yep, the classic. the one that's literally always there 🎀

🌸 SYNOPSIS 🌸

#include <sys/syscall.h>
#include <unistd.h>

int
syscall(int number, ...);

off_t
__syscall(quad_t number, ...);

two headers, two functions. that's the whole vibe check ✨

💖 DESCRIPTION 💖

okay so the way syscall() works is, it performs the system call whose assembly language interface has the specified number with the specified arguments. that's it, that's the whole thing — you hand it a number, it goes and does the syscall 💅

Symbolic constants for system calls can be found in the header file <sys/syscall.h. so like, please don't just memorize raw numbers, the constants are right there 🧚

the __syscall() form should be used when one or more of the arguments is a 64-bit argument to ensure that argument alignment is correct. lowkey important — misaligned args are not the moment, ngl 😭

this system call is useful for testing new system calls that do not have entries in the C library. so when the libc hasn't caught up yet and you're feeling brave? this is your girl. main character energy fr fr 👑

🔥 RETURN VALUES 🔥

the return values are defined by the system call being invoked. like, it's not gonna tell you here, it depends on what you asked for.

in general, a 0 return value indicates success 💚 a -1 return value indicates an error, and an error code is stored in errno. so if you get -1, go check errno, that's where the tea is 🍓

🦋 HISTORY 🦋

the syscall() function appeared in 4.0BSD. vintage! iconic! 💜

👑 BUGS 👑

there is no way to simulate system calls that have multiple return values such as pipe(2). so like, if a syscall hands back more than one thing? this trick just cannot do it. periodt 💀

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okay bestie that's the whole page 🌈 huge thanks to the Debian crew for this one — this version is from Debian, dated June 16, 1993, so it's older than most of your faves and it's still serving 💅✨ 🎀