Merge tag 'tracepoints-v6.19' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

Pull unused tracepoints update from Steven Rostedt:
"Detect unused tracepoints.

If a tracepoint i

Merge tag 'tracepoints-v6.19' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

Pull unused tracepoints update from Steven Rostedt:
"Detect unused tracepoints.

If a tracepoint is defined but never used (TRACE_EVENT() created but
no trace_<tracepoint>() called), it can take up to or more than 5K of
memory each. This can add up as there are around a hundred unused
tracepoints with various configs. That is 500K of wasted memory.

Add a make build parameter of "UT=1" to have the build warn if an
unused tracepoint is detected in the build. This allows detection of
unused tracepoints to be upstream so that outreachy and the mentoring
project can have new developers look for fixing them, without having
these warnings suddenly show up when someone upgrades their kernel.

When all known unused tracepoints are removed, then the "UT=1" build
parameter can be removed and unused tracepoints will always warn. This
will catch new unused tracepoints after the current ones have been
removed.

Summary:

- Separate out elf functions from sorttable.c

Move out the ELF parsing functions from sorttable.c so that the
tracing tooling can use it.

- Add a tracepoint verifier tool to the build process

If "UT=1" is added to the kernel command line, any unused
tracepoints will trigger a warning at build time.

- Do not warn about unused tracepoints for tracepoints that are
exported

There are sever cases where a tracepoint is created by the kernel
and used by modules. Since there's no easy way to detect if these
are truly unused since the users are in modules, if a tracepoint is
exported, assume it will eventually be used by a module. Note,
there's not many exported tracepoints so this should not be a
problem to ignore them.

- Have building of modules also detect unused tracepoints

Do not only check the main vmlinux for unused tracepoints, also
check modules. If a module is defining a tracepoint it should be
using it.

- Add the tracepoint-update program to the ignore file

The new tracepoint-update program needs to be ignored by git"

* tag 'tracepoints-v6.19' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
scripts: add tracepoint-update to the list of ignores files
tracing: Add warnings for unused tracepoints for modules
tracing: Allow tracepoint-update.c to work with modules
tracepoint: Do not warn for unused event that is exported
tracing: Add a tracepoint verification check at build time
sorttable: Move ELF parsing into scripts/elf-parse.[ch]

show more ...

tracing: Allow tracepoint-update.c to work with modules

In order for tracepoint-update.c to work with modules, it cannot error out
if both "__tracepoint_check" and "__tracepoints_strings" are not fo

tracing: Allow tracepoint-update.c to work with modules

In order for tracepoint-update.c to work with modules, it cannot error out
if both "__tracepoint_check" and "__tracepoints_strings" are not found.
When enabled, the vmlinux.o may be required to have both, but modules only
have these sections if they have tracepoints. Modules without tracepoints
will not have either. They should not fail to build because of that.

If one section exists the other one should too. Note, if a module defines
a tracepoint but doesn't use any, it can cause this to fail.

Add a new "--module" parameter to tracepoint-update to be used when
running on module code. It will not error out if this is set and both
sections are missing. If this is set, and only the "__tracepoint_check"
section is missing, it means the module has defined tracepoints but none
of them are used. In that case, it prints a warning that the module has
only unused tracepoints and exits normally to not fail the build.

If the "__tracepoint_check" section exists but not the
"__tracepoint_strings", then that is an error and should fail the build.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nicolas Schier <nicolas.schier@linux.dev>
Cc: Nick Desaulniers <nick.desaulniers+lkml@gmail.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Link: https://lore.kernel.org/20251022004453.255696445@kernel.org
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

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tracing: Add a tracepoint verification check at build time

If a tracepoint is defined via DECLARE_TRACE() or TRACE_EVENT() but never
called (via the trace_<tracepoint>() function), its metadata is s

tracing: Add a tracepoint verification check at build time

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

Note, when all the existing unused tracepoints are removed from the build,
the "UT=1" will be removed and this will always be enabled when
tracepoints are configured to warn on any new tracepoints. The reason this
isn't always enabled now is because it will introduce a lot of warnings
for the current unused tracepoints, and all bisects would end at this
commit for those warnings.

Link: https://lore.kernel.org/all/20250528114549.4d8a5e03@gandalf.local.home/

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nicolas Schier <nicolas.schier@linux.dev>
Cc: Nick Desaulniers <nick.desaulniers+lkml@gmail.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Link: https://lore.kernel.org/20251022004452.920728129@kernel.org
Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> # for using strings instead of pointers
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

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