syscall_get_nr(9)

✨ syscall_get_nr(9) ✨

okay so this is a page from the Kernel API Manual (section 9, kernel-land, very demure very mindful) and it's literally about figuring out which syscall a task is currently vibing in 💅

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🌸 NAME 🌸

syscall_get_nr — find what system call a task is executing

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🎀 SYNOPSIS 🎀

int syscall_get_nr (struct task_struct *task , struct pt_regs *regs );

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🦋 ARGUMENTS 🦋

• task — the task of interest. bestie it must be blocked, no exceptions, that's the whole vibe check 🫶
• regs — this is task_pt_regs of task. like, the registers of that task specifically, not some random other task's, iykyk

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💖 DESCRIPTION 💖

so here's the tea ☕ if task is executing a system call, or it's at system call tracing about to attempt one, this returns the system call number. slay, that's it, that's the number 🔥

but if task is not executing a system call — meaning it's blocked inside the kernel for a fault or a signal — then it returns -1. like, nothing's happening, no syscall, no number, just -1 😭

⚠️ okay important detail: this returns int even on 64-bit machines. only 32 bits of system call number can be meaningful. so if the actual arch value is 64 bits, this truncates to 32 bits, which means 0xffffffff means -1. yes really, that's the whole bit-truncation situation, no cap 💀

and the big one, the rule that matters:

🌟 it's only valid to call this when task is known to be blocked. not guessing. not hoping. known. periodt 👑

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🌈 SEE ALSO 🌈

• Kernel file ./include/asm-generic/syscall.h
• syscall_set_nr(9)
• syscall_rollback(9)
• syscall_get_error(9)
• syscall_get_return_value(9)
• syscall_set_return_value(9)
• syscall_get_arguments(9)
• syscall_set_arguments(9)
• syscall_get_arch(9)

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that's the whole page bestie, go read the whole syscall family, they're all iconic together 🧚💜

— from ./include/asm-generic, dated October 2026, mwah 💋