From b837a8bdc48925e6512412973b845c53cbe2b412 Mon Sep 17 00:00:00 2001 From: Namhyung Kim Date: Tue, 4 Nov 2014 10:14:33 +0900 Subject: [PATCH] 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 --- tools/perf/util/header.c | 2 +- tools/perf/util/machine.c | 16 ++++++++++++++-- 2 files changed, 15 insertions(+), 3 deletions(-) diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c index 3e2c156d9c6..76442caca37 100644 --- a/tools/perf/util/header.c +++ b/tools/perf/util/header.c @@ -1269,7 +1269,7 @@ static int __event_process_build_id(struct build_id_event *bev, dso__set_build_id(dso, &bev->build_id); - if (filename[0] == '[') + if (!is_kernel_module(filename, NULL)) dso->kernel = dso_type; build_id__sprintf(dso->build_id, sizeof(dso->build_id), diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c index 946c7d62cb6..53f90e9c65f 100644 --- a/tools/perf/util/machine.c +++ b/tools/perf/util/machine.c @@ -1085,8 +1085,20 @@ static int machine__process_kernel_mmap_event(struct machine *machine, * Should be there already, from the build-id table in * the header. */ - struct dso *kernel = __dsos__findnew(&machine->kernel_dsos, - kmmap_prefix); + struct dso *kernel = NULL; + struct dso *dso; + + list_for_each_entry(dso, &machine->kernel_dsos.head, node) { + if (is_kernel_module(dso->long_name, NULL)) + continue; + + kernel = dso; + break; + } + + if (kernel == NULL) + kernel = __dsos__findnew(&machine->kernel_dsos, + kmmap_prefix); if (kernel == NULL) goto out_problem; -- 2.46.0