On Wed, Oct 15, 2025 at 04:38:44PM -0400, Steven Rostedt wrote: > From: Steven Rostedt <[email protected]> > > If a tracepoint is defined via DECLARE_TRACE() or TRACE_EVENT() but never > called (via the trace_<tracepoint>() function), its metadata is still > around in memory and not discarded. > > When created via TRACE_EVENT() the situation is worse because the > TRACE_EVENT() creates metadata that can be around 5k per trace event. > Having unused trace events causes several thousand of wasted bytes. > > Add a verifier that injects a string of the name of the tracepoint it > calls that is added to the discarded section "__tracepoint_check". > For every builtin tracepoint, its name (which is saved in the in-memory > section "__tracepoint_strings") will have its name also in the > "__tracepoint_check" section if it is used. > > Add a new program that is run on build called tracepoint-update. This is > executed on the vmlinux.o before the __tracepoint_check section is > discarded (the section is discarded before vmlinux is created). This > program will create an array of each string in the __tracepoint_check > section and then sort it. Then it will walk the strings in the > __tracepoint_strings section and do a binary search to check if its name > is in the __tracepoint_check section. If it is not, then it is unused and > a warning is printed. > > Note, this currently only handles tracepoints that are builtin and not in > modules. > > Enabling this currently with a given config produces: > > warning: tracepoint 'sched_move_numa' is unused. > warning: tracepoint 'sched_stick_numa' is unused. > warning: tracepoint 'sched_swap_numa' is unused. > warning: tracepoint 'pelt_hw_tp' is unused. > warning: tracepoint 'pelt_irq_tp' is unused. > warning: tracepoint 'rcu_preempt_task' is unused. > warning: tracepoint 'rcu_unlock_preempted_task' is unused. > warning: tracepoint 'xdp_bulk_tx' is unused. > warning: tracepoint 'xdp_redirect_map' is unused. > warning: tracepoint 'xdp_redirect_map_err' is unused. > warning: tracepoint 'vma_mas_szero' is unused. > warning: tracepoint 'vma_store' is unused. > warning: tracepoint 'hugepage_set_pmd' is unused. > warning: tracepoint 'hugepage_set_pud' is unused. > warning: tracepoint 'hugepage_update_pmd' is unused. > warning: tracepoint 'hugepage_update_pud' is unused. > warning: tracepoint 'block_rq_remap' is unused. > warning: tracepoint 'xhci_dbc_handle_event' is unused. > warning: tracepoint 'xhci_dbc_handle_transfer' is unused. > warning: tracepoint 'xhci_dbc_gadget_ep_queue' is unused. > warning: tracepoint 'xhci_dbc_alloc_request' is unused. > warning: tracepoint 'xhci_dbc_free_request' is unused. > warning: tracepoint 'xhci_dbc_queue_request' is unused. > warning: tracepoint 'xhci_dbc_giveback_request' is unused. > warning: tracepoint 'tcp_ao_wrong_maclen' is unused. > warning: tracepoint 'tcp_ao_mismatch' is unused. > warning: tracepoint 'tcp_ao_key_not_found' is unused. > warning: tracepoint 'tcp_ao_rnext_request' is unused. > warning: tracepoint 'tcp_ao_synack_no_key' is unused. > warning: tracepoint 'tcp_ao_snd_sne_update' is unused. > warning: tracepoint 'tcp_ao_rcv_sne_update' is unused. > > Some of the above is totally unused but others are not used due to their > "trace_" functions being inside configs, in which case, the defined > tracepoints should also be inside those same configs. Others are > architecture specific but defined in generic code, where they should > either be moved to the architecture or be surrounded by #ifdef for the > architectures they are for. > > This tool could be updated to process modules in the future. > > I'd like to thank Mathieu Desnoyers for suggesting using strings instead > of pointers, as using pointers in vmlinux.o required handling relocations > and it required implementing almost a full feature linker to do so. > > To enable this check, run the build with: make UT=1 > > Link: https://lore.kernel.org/all/[email protected]/ > > Suggested-by: Mathieu Desnoyers <[email protected]> # for using > strings instead of pointers > Signed-off-by: Steven Rostedt (Google) <[email protected]> > --- > Changes since v8: https://lore.kernel.org/[email protected] > > - Instead of using a config option to enable this, enable it via: make UT=1 > This will allow it to go into linux-next without triggering all the > current warnings but also allow people to find and fix current unused > tracepoints. > > Makefile | 15 ++ > include/asm-generic/vmlinux.lds.h | 1 + > include/linux/tracepoint.h | 11 ++ > scripts/Makefile | 3 + > scripts/link-vmlinux.sh | 7 + > scripts/tracepoint-update.c | 232 ++++++++++++++++++++++++++++++ > 6 files changed, 269 insertions(+) > create mode 100644 scripts/tracepoint-update.c > > diff --git a/Makefile b/Makefile > index 17cfa11ca716..a3141890f38f 100644 > --- a/Makefile > +++ b/Makefile > @@ -157,6 +157,20 @@ endif > > export KBUILD_EXTRA_WARN > > +# To check for unused tracepoints (tracepoints that are defined but never > +# called), run with: > +# > +# make UT=1 > +# > +# Each unused tracepoints can take up to 5KB of memory in the running kernel. > +# It is best to remove any that are not used. > + > +ifeq ("$(origin UT)", "command line") > + WARN_ON_UNUSED_TRACEPOINTS := $(UT) > +endif > + > +export WARN_ON_UNUSED_TRACEPOINTS
Is there a special reason why you chose to introduce a new command-line variable instead of extending KBUILD_EXTRA_WARN / W ? Kind regards, Nicolas
