Every trace event can take up to 5K of memory in text and meta data regardless if they are used or not. Trace events should not be created if they are not used. Currently there's over a hundred events in the kernel that are defined but unused, either because their callers were removed without removing the trace event with it, or a config hides the trace event caller but not the trace event itself. And in some cases, trace events were simply added but were never called for whatever reason. The number of unused trace events continues to grow.
This patch series aims to fix this. The first patch creates a new section called __tracepoint_check, where all callers of a tracepoint creates a variable that is placed in this section with a pointer to the tracepoint they use. Then on boot up, it iterates this section and will modify the tracepoint's "func" field to a value of 1 (all tracepoints "func" fields are initialized to NULL and is only set when they are registered). This takes place before any tracepoint can be registered. Then each tracepoint is iterated on and if any tracepoint does not have its "func" field set to 1 a warning is triggerd and every tracepoint that doesn't have that field set is printed. The "func" field is then reset back to NULL. The second patch modifies scripts/sorttable.c to read the __tracepoint_check section. It sorts it, and then reads the __tracepoint_ptr section that has all compiled in tracepoints. It makes sure that every tracepoint is found in the check section and if not, it prints a warning message about it. This lists the missing tracepoints at build time. The third patch updates sorttable to work for arm64 when compiled with gcc. As gcc's arm64 build doesn't put addresses in their section but saves them off in the RELA sections. This mostly takes the work done that was needed to do the mcount sorting at boot up on arm64. The forth patch adds EXPORT_TRACEPOINT() to the __tracepoint_check section as well. There was several locations that adds tracepoints in the kernel proper that are only used in modules. It was getting quite complex trying to move things around that I just decided to make any tracepoint in a EXPORT_TRACEPOINT "used". I'm using the analogy of static and global functions. An unused static function gets a warning but an unused global one does not. The last patch updates the trace_ftrace_test_filter boot up self test. That selftest creates a trace event to run a bunch of filter tests on it without actually calling the tracepoint. To quiet the warning, the selftest tracepoint is called within a if (!trace_<event>_enabled()) section, where it will not be optimized out, nor will it be called. This is v2 from: https://lore.kernel.org/linux-trace-kernel/20250529130138.544ff...@gandalf.local.home/ which was simply the first patch. This version adds the other patches. Steven Rostedt (5): tracepoints: Add verifier that makes sure all defined tracepoints are used tracing: sorttable: Add a tracepoint verification check at build time tracing: sorttable: Find unused tracepoints for arm64 that uses reloc for address tracepoint: Do not warn for unused event that is exported tracing: Call trace_ftrace_test_filter() for the event ---- include/asm-generic/vmlinux.lds.h | 1 + include/linux/tracepoint.h | 13 ++ kernel/trace/Kconfig | 31 +++ kernel/trace/trace_events_filter.c | 4 + kernel/tracepoint.c | 26 +++ scripts/Makefile | 4 + scripts/sorttable.c | 444 ++++++++++++++++++++++++++++++------- 7 files changed, 437 insertions(+), 86 deletions(-)
