With CONFIG_KPROBES_ON_FTRACE enabled on powerpc, ftrace_location_range returns ftrace location for bpf_fentry_test1 at offset of 4 bytes from function entry. This is because branch to _mcount function is at offset of 4 bytes in function profile sequence.

To fix this, add entry_offset of 4 bytes while verifying the address for kprobe entry address of bpf_fentry_test1 in verify_perf_link_info in selftest, when CONFIG_KPROBES_ON_FTRACE is enabled.

Disassemble of bpf_fentry_test1:

c000000000e4b080 <bpf_fentry_test1>: c000000000e4b080: a6 02 08 7c mflr r0 c000000000e4b084: b9 e2 22 4b bl c00000000007933c <_mcount> c000000000e4b088: 01 00 63 38 addi r3,r3,1 c000000000e4b08c: b4 07 63 7c extsw r3,r3 c000000000e4b090: 20 00 80 4e blr

When CONFIG_PPC_FTRACE_OUT_OF_LINE [1] is enabled, these function profile sequence is moved out of line with an unconditional branch at offset 0. So, the test works without altering the offset for 'CONFIG_KPROBES_ON_FTRACE && CONFIG_PPC_FTRACE_OUT_OF_LINE' case.

Disassemble of bpf_fentry_test1:

c000000000f95190 <bpf_fentry_test1>: c000000000f95190: 00 00 00 60 nop c000000000f95194: 01 00 63 38 addi r3,r3,1 c000000000f95198: b4 07 63 7c extsw r3,r3 c000000000f9519c: 20 00 80 4e blr

[1] https://lore.kernel.org/all/20241030070850.1361304-13-hbathini@linux.ibm.com...

Fixes: 23cf7aa539dc ("selftests/bpf: Add selftest for fill_link_info") Signed-off-by: Saket Kumar Bhaskar skb99@linux.ibm.com --- .../selftests/bpf/prog_tests/fill_link_info.c | 4 ++++ .../selftests/bpf/progs/test_fill_link_info.c | 13 ++++++++++--- 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/fill_link_info.c b/tools/testing/selftests/bpf/prog_tests/fill_link_info.c index d50cbd804..e59af2aa6 100644 --- a/tools/testing/selftests/bpf/prog_tests/fill_link_info.c +++ b/tools/testing/selftests/bpf/prog_tests/fill_link_info.c @@ -171,6 +171,10 @@ static void test_kprobe_fill_link_info(struct test_fill_link_info *skel, /* See also arch_adjust_kprobe_addr(). */ if (skel->kconfig->CONFIG_X86_KERNEL_IBT) entry_offset = 4; + if (skel->kconfig->CONFIG_PPC64 && + skel->kconfig->CONFIG_KPROBES_ON_FTRACE && + !skel->kconfig->CONFIG_PPC_FTRACE_OUT_OF_LINE) + entry_offset = 4; err = verify_perf_link_info(link_fd, type, kprobe_addr, 0, entry_offset); ASSERT_OK(err, "verify_perf_link_info"); } else { diff --git a/tools/testing/selftests/bpf/progs/test_fill_link_info.c b/tools/testing/selftests/bpf/progs/test_fill_link_info.c index 6afa83475..fac33a14f 100644 --- a/tools/testing/selftests/bpf/progs/test_fill_link_info.c +++ b/tools/testing/selftests/bpf/progs/test_fill_link_info.c @@ -6,13 +6,20 @@ #include <stdbool.h>

extern bool CONFIG_X86_KERNEL_IBT __kconfig __weak; +extern bool CONFIG_PPC_FTRACE_OUT_OF_LINE __kconfig __weak; +extern bool CONFIG_KPROBES_ON_FTRACE __kconfig __weak; +extern bool CONFIG_PPC64 __kconfig __weak;

-/* This function is here to have CONFIG_X86_KERNEL_IBT - * used and added to object BTF. +/* This function is here to have CONFIG_X86_KERNEL_IBT, + * CONFIG_PPC_FTRACE_OUT_OF_LINE, CONFIG_KPROBES_ON_FTRACE, + * CONFIG_PPC6 used and added to object BTF. */ int unused(void) { - return CONFIG_X86_KERNEL_IBT ? 0 : 1; + return CONFIG_X86_KERNEL_IBT || + CONFIG_PPC_FTRACE_OUT_OF_LINE || + CONFIG_KPROBES_ON_FTRACE || + CONFIG_PPC64 ? 0 : 1; }

SEC("kprobe")