ftrace_bug(9)

💅 ftrace_bug — a Kernel API Manual moment (section 9, bestie)

okay so this is ftrace_bug(9) from the Kernel API Manual, and it's literally the function that catches the function tracer mid-crisis and shuts the whole thing down. it's giving "we need to talk" energy 🫶

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✨ NAME ✨

ftrace_bug — report and shutdown function tracer. yes bestie, both: it snitches AND it pulls the plug 😭

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🌸 SYNOPSIS 🌸

void ftrace_bug (int failed , struct dyn_ftrace *rec );

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🎀 ARGUMENTS 🎀

• failed — the failed type, and it's gotta be one of EFAULT, EINVAL, EPERM. no vibes-based error codes allowed 🙈
• rec — the record that failed. the actual struct dyn_ftrace that did the mess 💀

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🦋 DESCRIPTION 🦋

so the arch code — the one that enables or disables the function tracing — can call ftrace_bug when it has detected a problem in modifying the code. that's the whole point of it, it's the "hey something went sideways while we were poking at instructions" hotline 🔥

and failed should be one of either:

• EFAULT — if the problem happens on reading the ip address 👀
• EINVAL — if what is read at ip is not what was expected 😬
• EPERM — if the problem happens on writing to the ip address 🚫

like, each code tells you where in the read/write dance things went wrong, iykyk. use the right one, don't just pick your fave 💅

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⭐ SEE ALSO ⭐

Kernel file ./kernel/trace/ftrace.c

• ftrace_lookup_ip(9)
• ftrace_free_filter(9)
• ftrace_hash_move(9)
• ftrace_location_range(9)
• ftrace_location(9)
• ftrace_text_reserved(9)
• ftrace_update_record(9)
• ftrace_test_record(9)
• ftrace_get_addr_new(9)
• ftrace_get_addr_curr(9)
• ftrace_rec_iter_start(9)
• ftrace_rec_iter_next(9)
• ftrace_rec_iter_record(9)
• ftrace_run_stop_machine(9)
• arch_ftrace_update_code(9)
• ftrace_startup_subops(9)
• ftrace_shutdown_subops(9)
• ftrace_regex_open(9)
• allocate_ftrace_func_mapper(9)
• ftrace_func_mapper_find_ip(9)
• ftrace_func_mapper_add_ip(9)
• ftrace_func_mapper_remove_ip(9)
• free_ftrace_func_mapper(9)
• register_ftrace_direct(9)
• unregister_ftrace_direct(9)
• modify_ftrace_direct_nolock(9)
• modify_ftrace_direct(9)
• hash_add(9)
• update_ftrace_direct_add(9)
• hash_sub(9)
• update_ftrace_direct_del(9)
• update_ftrace_direct_mod(9)
• ftrace_set_filter_ip(9)
• ftrace_set_filter_ips(9)
• ftrace_ops_set_global_filter(9)
• ftrace_set_filter(9)
• ftrace_set_notrace(9)
• ftrace_set_global_filter(9)
• ftrace_set_global_notrace(9)
• ftrace_ops_get_func(9)
• ftrace_kill(9)
• ftrace_is_dead(9)
• register_ftrace_function(9)
• unregister_ftrace_function(9)
• ftrace_lookup_symbols(9)

like, that's the whole ftrace friend group right there, go say hi 🌈

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ngl this whole page lives in ./kernel/trace and it's dated October 2026 — so yeah, this manual page is from the future and it's still out here documenting a bug reporter. main character energy fr fr 👑✨💜