Re: [PATCH 3/3] objtool/klp: Add test for changed functions without an ftrace call site

[Joe Lawrence <joe.lawrence@redhat.com>]

On Thu, Oct 22, 2026 at 05:25:38AM -0700, Puranjay Mohan wrote:
> Test that klp diff rejects a changed function without an ftrace call
> site, both a notrace one and an inline one emitted out of line, and
> reports each of them.  Also test that a fully inlined function and an
> ordinary function can still be patched.
> 
> Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
> ---
>  .../tests/x86/fixtures/notrace_target.c       | 71 ++++++++++++++++++
>  .../objtool/tests/x86/test-notrace-target.sh  | 74 +++++++++++++++++++
>  2 files changed, 145 insertions(+)
>  create mode 100644 tools/objtool/tests/x86/fixtures/notrace_target.c
>  create mode 100755 tools/objtool/tests/x86/test-notrace-target.sh
> 
> diff --git a/tools/objtool/tests/x86/fixtures/notrace_target.c b/tools/objtool/tests/x86/fixtures/notrace_target.c
> new file mode 100644
> index 0000000000000..64da58c872b8a
> --- /dev/null
> +++ b/tools/objtool/tests/x86/fixtures/notrace_target.c
> @@ -0,0 +1,71 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* PATCH_<name> changes <name> in the patched build. */
> +#define notrace __attribute__((__no_instrument_function__))
> +
> +static const char __modinfo[]
> +	__attribute__((section(".modinfo"), used, aligned(1))) = "\0name=vmlinux";
> +
> +#ifndef PATCHED
> +#undef PATCH_OUTLINED
> +#undef PATCH_NOTRACE
> +#undef PATCH_INLINED
> +#undef PATCH_TRACED
> +#endif
> +
> +#ifdef PATCH_OUTLINED
> +#define OUTLINED_K 2
> +#else
> +#define OUTLINED_K 1
> +#endif
> +
> +#ifdef PATCH_NOTRACE
> +#define NOTRACE_K 2
> +#else
> +#define NOTRACE_K 1
> +#endif
> +
> +#ifdef PATCH_INLINED
> +#define INLINED_K 2
> +#else
> +#define INLINED_K 1
> +#endif
> +
> +#ifdef PATCH_TRACED
> +#define TRACED_K 2
> +#else
> +#define TRACED_K 1
> +#endif
> +
> +int sink;
> +
> +/* Address taken, so emitted out of line. */
> +static inline notrace int outlined(int x)
> +{
> +	int i;
> +
> +	for (i = 0; i < x; i++)
> +		sink += i * OUTLINED_K;
> +	return sink;
> +}
> +
> +int (*outlined_ptr)(int) = outlined;
> +
> +notrace int notrace_fn(int x)
> +{
> +	return x * 3 + NOTRACE_K;
> +}
> +
> +static inline int inlined(int x)
> +{
> +	return x + INLINED_K;
> +}
> +
> +int inlined_user(int x)
> +{
> +	return inlined(x) * 5;
> +}
> +
> +int traced(int x)
> +{
> +	return x * 7 + TRACED_K;
> +}
> diff --git a/tools/objtool/tests/x86/test-notrace-target.sh b/tools/objtool/tests/x86/test-notrace-target.sh
> new file mode 100755
> index 0000000000000..09414ae65fc2c
> --- /dev/null
> +++ b/tools/objtool/tests/x86/test-notrace-target.sh
> @@ -0,0 +1,74 @@
> +#!/bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +#
> +# A changed function without an ftrace call site can't be livepatched:
> +# klp_enable_patch() fails with "failed to find location for function".
> +# klp diff must reject it instead.
> +
> +. "$(dirname "$0")/../lib.sh"
> +
> +# mcount_entry <function>: orig.o has an __mcount_loc entry for it.
> +mcount_entry()
> +{
> +	in_relocs "$orig_obj" | awk '/rela__mcount_loc/,/^$/' |
> +		awk -v f="$1" '$5 == f || $5 == ".text." f' | grep -q .
> +}
> +
> +# check <expected exit status> <-DPATCH_... flags>
> +check()
> +{
> +	local expect="$1"; shift
> +
> +	setup
> +	build_pair notrace_target.c "$@"
> +
> +	assert_input_symbol outlined
> +	assert_input_symbol notrace_fn
> +	has_input_symbol "$orig_obj" inlined &&
> +		fail "inlined() was emitted out of line; the fixture tests nothing"
> +	mcount_entry traced ||
> +		fail "no __mcount_loc entry for traced(); the fixture tests nothing"
> +	mcount_entry inlined_user ||
> +		fail "no __mcount_loc entry for inlined_user(); the fixture tests nothing"
> +	mcount_entry outlined &&
> +		fail "outlined() has a __mcount_loc entry; it should be notrace"
> +	mcount_entry notrace_fn &&
> +		fail "notrace_fn() has a __mcount_loc entry; it should be notrace"
> +
> +	run_diff "$expect"
> +}
> +
> +rejected()
> +{
> +	local n
> +
> +	n="$(diff_log | grep -c "error: objtool: $1: no ftrace call site, can't patch")"
> +	[ "$n" = 1 ] ||
> +		fail "expected '$1' rejected once, found $n: $(diff_log | tail -2)"
> +}
> +
> +check 255 -DPATCH_OUTLINED
> +rejected outlined
> +cleanup
> +
> +check 255 -DPATCH_NOTRACE
> +rejected notrace_fn
> +cleanup
> +
> +check 255 -DPATCH_OUTLINED -DPATCH_NOTRACE
> +rejected outlined
> +rejected notrace_fn
> +cleanup
> +
> +# Fully inlined: the traceable caller gets patched.
> +check 0 -DPATCH_INLINED
> +assert_patched inlined_user
> +assert_not_patched traced
> +cleanup
> +
> +check 0 -DPATCH_TRACED
> +assert_patched traced
> +assert_not_patched inlined_user
> +cleanup
> +
> +pass "changed function without an ftrace call site rejected"
> -- 
> 2.53.0-Meta
> 
> 

Thanks for finding and fixing this bug!  By coincidence, I was debugging
this very problem yesterday (wondering why I couldn't load a patch that
modified an un-patchable function).

Acked-by: Joe Lawrence <joe.lawrence@redhat.com>

--
Joe