Re: [PATCH] Remove kretprobe_trampoline_holder.
From: Michael Ellerman <mpe@ellerman.id.au>
Date: 2016-03-29 03:31:34
On Mon, 2016-03-28 at 17:06 -0300, Thiago Jung Bauermann wrote:
quoted hunk ↗ jump to hunk
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, all vmlinux symbols match /proc/kallsyms and the testcase passes.
Have you tested this on an LE system? I did a quick test and it appears to be completely broken. Basically every symbol is not found, eg: 1: vmlinux symtab matches kallsyms :
--- start ---test child forked, pid 16222 Using /proc/kcore for kernel object code Looking at the vmlinux_path (8 entries long) Using /boot/vmlinux-4.5.0-11318-gdf01bc5cf4ea for symbols 0xc00000000000b428: run_init_process not on kallsyms 0xc00000000000b478: try_to_run_init_process not on kallsyms 0xc00000000000b4f8: do_one_initcall not on kallsyms 0xc00000000000b768: match_dev_by_uuid not on kallsyms ... 0xc0000000009846b8: write_mem not on kallsyms 0xc000000000984728: do_fp_store not on kallsyms 0xc000000000984828: emulate_step not on kallsyms $ sudo grep emulate_step /proc/kallsyms c000000000984820 T emulate_step Notice it's off by 8. That's because of the local/global entry point on LE. So that will need to be fixed somewhere. cheers