From: Namhyung Kim Date: Tue, 4 Nov 2014 01:14:33 +0000 (+0900) Subject: perf tools: Fix build-id matching on vmlinux X-Git-Tag: omap-for-v3.19/fixes-rc1~167^2~15^2~5 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b837a8bdc48925e6512412973b845c53cbe2b412;p=pandora-kernel.git perf tools: Fix build-id matching on vmlinux There's a problem on finding correct kernel symbols when perf report runs on a different kernel. Although a part of the problem was solved by the prior commit 0a7e6d1b6844 ("perf tools: Check recorded kernel version when finding vmlinux"), there's a remaining problem still. When perf records samples, it synthesizes the kernel map using machine__mmap_name() and ref_reloc_sym like "[kernel.kallsyms]_text". You can easily see it using 'perf report -D' command. After finishing record, it goes through the recorded events to find maps/dsos actually used. And then record build-id info of them. During this process, it needs to load symbols in a dso and it'd call dso__load_vmlinux_path() since the default value of the symbol_conf. try_vmlinux_path is true. However it changes dso->long_name to a real path of the vmlinux file (e.g. /lib/modules/3.16.4/build/vmlinux) if one is running on a custom kernel. It resulted in that perf report reads the build-id of the vmlinux, but cannot use it since it only knows about the [kernel.kallsyms] map. It then falls back to possible vmlinux paths by using the recorded kernel version (in case of a recent version) or a running kernel silently. Even with the recent tools, this still has a possibility of breaking the result. As the build directory is a symbolic link, if one built a new kernel in the same directory with different source/config, the old link to vmlinux will point the new file. So it's absolutely needed to use build-id when finding a kernel image. In this patch, it's now changed to try to search a kernel dso in the existing dso list which was constructed during build-id table parsing so it'll always have a build-id. If not found, search "[kernel.kallsyms]". Before: $ perf report # Children Self Command Shared Object Symbol # ........ ........ ....... ................. ............................... # 72.15% 0.00% swapper [kernel.kallsyms] [k] set_curr_task_rt 72.15% 0.00% swapper [kernel.kallsyms] [k] native_calibrate_tsc 72.15% 0.00% swapper [kernel.kallsyms] [k] tsc_refine_calibration_work 71.87% 71.87% swapper [kernel.kallsyms] [k] module_finalize ... After (for the same perf.data): 72.15% 0.00% swapper vmlinux [k] cpu_startup_entry 72.15% 0.00% swapper vmlinux [k] arch_cpu_idle 72.15% 0.00% swapper vmlinux [k] default_idle 71.87% 71.87% swapper vmlinux [k] native_safe_halt ... Signed-off-by: Namhyung Kim Acked-by: Ingo Molnar Link: http://lkml.kernel.org/r/20140924073356.GB1962@gmail.com Cc: Adrian Hunter Cc: David Ahern Cc: Ingo Molnar Cc: Jiri Olsa Cc: Namhyung Kim Cc: Paul Mackerras Cc: Peter Zijlstra Cc: Stephane Eranian Link: http://lkml.kernel.org/r/1415063674-17206-8-git-send-email-namhyung@kernel.org Signed-off-by: Arnaldo Carvalho de Melo --- Reading git-diff-tree failed