Fixes the following testsuite failure: $ sudo ./perf test -v kallsyms 1: vmlinux symtab matches kallsyms : --- start --- test child forked, pid 12489 Using /proc/kcore for kernel object code Looking at the vmlinux_path (8 entries long) Using /boot/vmlinux for symbols 0xc00000000003d300: diff name v: .kretprobe_trampoline_holder k: kretprobe_trampoline Maps only in vmlinux: c00000000086ca38-c000000000879b6c 87ca38 [kernel].text.unlikely c000000000879b6c-c000000000bf0000 889b6c [kernel].meminit.text c000000000bf0000-c000000000c53264 c00000 [kernel].init.text c000000000c53264-d000000004250000 c63264 [kernel].exit.text d000000004250000-d000000004450000 0 [libcrc32c] d000000004450000-d000000004620000 0 [xfs] d000000004620000-d000000004680000 0 [autofs4] d000000004680000-d0000000046e0000 0 [x_tables] d0000000046e0000-d000000004780000 0 [ip_tables] d000000004780000-d0000000047e0000 0 [rng_core] d0000000047e0000-ffffffffffffffff 0 [pseries_rng] Maps in vmlinux with a different name in kallsyms: Maps only in kallsyms: d000000000000000-f000000000000000 1000000000010000 [kernel.kallsyms] f000000000000000-ffffffffffffffff 3000000000010000 [kernel.kallsyms] test child finished with -1 ---- end ---- vmlinux symtab matches kallsyms: FAILED!
The problem is that the kretprobe_trampoline symbol looks like this: $ eu-readelf -s /boot/vmlinux G kretprobe_trampoline 2431: c000000001302368 24 NOTYPE LOCAL DEFAULT 37 kretprobe_trampoline_holder 2432: c00000000003d300 8 FUNC LOCAL DEFAULT 1 .kretprobe_trampoline_holder 97543: c00000000003d300 0 NOTYPE GLOBAL DEFAULT 1 kretprobe_trampoline Its type is NOTYPE, and its size is 0, and this is a problem because symbol-elf.c:dso__load_sym skips function symbols that are not STT_FUNC or STT_GNU_IFUNC (this is determined by elf_sym__is_function). Even if the type is changed to STT_FUNC, when dso__load_sym calls symbols__fixup_duplicate, the kretprobe_trampoline symbol is dropped in favour of .kretprobe_trampoline_holder because the latter has non-zero size (as determined by choose_best_symbol). With this patch, during symbol deduplication kretprobe_trampoline is used instead of .kretprobe_trampoline_holder, making all vmlinux symbols match /proc/kallsyms and the testcase passes. Alternatively, I just noticed that commit c1c355c was merged and it gets rid of kretprobe_trampoline_holder altogether on x86. I believe that would fix this problem as well, but I don't know enough about kprobes to know whether kretprobe_trampoline_holder has any use on powerpc. Signed-off-by: Thiago Jung Bauermann <[email protected]> --- arch/powerpc/kernel/kprobes.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c index 7c053f2..068f2f9 100644 --- a/arch/powerpc/kernel/kprobes.c +++ b/arch/powerpc/kernel/kprobes.c @@ -281,8 +281,10 @@ no_kprobe: static void __used kretprobe_trampoline_holder(void) { asm volatile(".global kretprobe_trampoline\n" + ".type kretprobe_trampoline, @function\n" "kretprobe_trampoline:\n" - "nop\n"); + "nop\n" + ".size kretprobe_trampoline, .-kretprobe_trampoline\n"); } /* -- 1.9.1 _______________________________________________ Linuxppc-dev mailing list [email protected] https://lists.ozlabs.org/listinfo/linuxppc-dev
