Message ID | 1458839824-27844-1-git-send-email-bauerman@linux.vnet.ibm.com (mailing list archive) |
---|---|
State | Changes Requested |
Headers | show |
On Thu, 2016-24-03 at 17:17:04 UTC, Thiago Jung Bauermann wrote: > 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. Thanks, good change log. > 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. I don't see any reason why we need it on powerpc. So can you try removing kretprobe_trampoline_holder and check that kretprobes still work. And then confirm that it also fixes this bug? cheers
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"); } /*
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 <bauerman@linux.vnet.ibm.com> --- arch/powerpc/kernel/kprobes.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)