SYSCALL(2)

💖 SYSCALL(2) 💖

okay bestie, welcome to the System Calls Manual entry for SYSCALL(2) — yes we're going indirect, it's giving ✨middleware energy✨ and honestly? iconic.

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🌸 NAME 🌸

syscall, __syscall — indirect system call 🦋

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📚 LIBRARY 📚

Standard C Library (libc, -lc) 🎀

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✨ SYNOPSIS ✨

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

int
syscall(int number, ...);

off_t
__syscall(quad_t number, ...);

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💅 DESCRIPTION 💅

so the way that syscall() works is: it performs the system call whose assembly language interface has the specified number with the specified arguments. fr fr, that's the whole vibe. 🫶

the symbolic constants for system calls can be found in the header file <sys/syscall.h>. go look, they're all in there, no cap. 🔥

now, the __syscall() form should be used when one or more of the arguments is a 64-bit argument — that's the one that makes sure your argument alignment is correct. don't skip it, bestie, alignment matters. 💀

and like, what is this even for? this system call is useful for testing new system calls that do not have entries in the C library. it's the VIP backstage pass for syscalls that haven't been officially introduced to libc yet. main character energy for real. 👑

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🌈 RETURN VALUES 🌈

the return values are defined by the system call being invoked — so like, it's not a fixed thing, it depends on which syscall you poked. 🙈

in general:

• a 0 return value indicates success ✨
• a -1 return value indicates an error, and an error code is stored in errno 😭

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🕰️ HISTORY 🕰️

the syscall() function appeared in 4.0BSD. vintage. antique. historical queen. 👑

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🐛 BUGS 🐛

there is no way to simulate system calls that have multiple return values such as pipe(2). that's it, that's the bug, we're all just living with it. 💀

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and that's the whole page, bestie 💖 this one came to you from Debian, dated June 16, 1993 — yeah it's older than us but it still ate. mwah. 🎀✨🦋