Path: csiph.com!eternal-september.org!feeder.eternal-september.org!aioe.org!bofh.it!news.nic.it!robomod From: Wang Nan Newsgroups: linux.kernel Subject: [PATCH] perf probe: Try to use symbol table if searching debug info failed Date: Thu, 20 Aug 2015 06:30:01 +0200 Message-ID: X-Original-To: , , , X-Mailer: git-send-email 1.8.3.4 MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [10.107.193.248] X-Cfilter-Loop: Reflected Sender: robomod@news.nic.it List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Approved: robomod@news.nic.it Lines: 83 Organization: linux.* mail to news gateway X-Original-Cc: , , X-Original-Date: Thu, 20 Aug 2015 04:25:04 +0000 X-Original-Message-ID: <1440044704-122048-1-git-send-email-wangnan0@huawei.com> X-Original-Sender: linux-kernel-owner@vger.kernel.org Xref: csiph.com linux.kernel:1210138 A problem can occure in statically linked perf when vmlinux can be found: # perf probe --add sys_epoll_pwait probe-definition(0): sys_epoll_pwait symbol:sys_epoll_pwait file:(null) line:0 offset:0 return:0 lazy:(null) 0 arguments Looking at the vmlinux_path (7 entries long) Using /lib/modules/4.2.0-rc1+/build/vmlinux for symbols Open Debuginfo file: /lib/modules/4.2.0-rc1+/build/vmlinux Try to find probe point from debuginfo. Symbol sys_epoll_pwait address found : ffffffff8122bd40 Matched function: SyS_epoll_pwait Failed to get call frame on 0xffffffff8122bd40 An error occurred in debuginfo analysis (-2). Error: Failed to add events. Reason: No such file or directory (Code: -2) The reason is caused by libdw that, if libdw is statically linked, it can't load libebl_{arch}.so reliable. In this case it is still possible to get the address from /proc/kalksyms. However, perf tries that only when libdw returns -EBADF. This patch gives it another chance to utilize symbol table, even if libdw return error code other than -EBADF. After applying this patch: # perf probe -nv --add sys_epoll_pwait probe-definition(0): sys_epoll_pwait symbol:sys_epoll_pwait file:(null) line:0 offset:0 return:0 lazy:(null) 0 arguments Looking at the vmlinux_path (7 entries long) Using /lib/modules/4.2.0-rc1+/build/vmlinux for symbols Open Debuginfo file: /lib/modules/4.2.0-rc1+/build/vmlinux Try to find probe point from debuginfo. Symbol sys_epoll_pwait address found : ffffffff8122bd40 Matched function: SyS_epoll_pwait Failed to get call frame on 0xffffffff8122bd40 An error occurred in debuginfo analysis (-2). Trying to use symbols. Opening /sys/kernel/debug/tracing/kprobe_events write=1 Added new event: Writing event: p:probe/sys_epoll_pwait _text+2276672 probe:sys_epoll_pwait (on sys_epoll_pwait) You can now use it in all perf tools, such as: perf record -e probe:sys_epoll_pwait -aR sleep 1 Although libdw returns an error (Failed to get call frame), perf tries symbol table and finally gets correct address. Signed-off-by: Wang Nan --- tools/perf/util/probe-event.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c index fe4941a..f07374b 100644 --- a/tools/perf/util/probe-event.c +++ b/tools/perf/util/probe-event.c @@ -705,9 +705,10 @@ static int try_to_find_probe_trace_events(struct perf_probe_event *pev, } /* Error path : ntevs < 0 */ pr_debug("An error occurred in debuginfo analysis (%d).\n", ntevs); - if (ntevs == -EBADF) { - pr_warning("Warning: No dwarf info found in the vmlinux - " - "please rebuild kernel with CONFIG_DEBUG_INFO=y.\n"); + if (ntevs < 0) { + if (ntevs == -EBADF) + pr_warning("Warning: No dwarf info found in the vmlinux - " + "please rebuild kernel with CONFIG_DEBUG_INFO=y.\n"); if (!need_dwarf) { pr_debug("Trying to use symbols.\n"); return 0; -- 1.8.3.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/