From b119970aa541091e405373399690c24ead9d2920 Mon Sep 17 00:00:00 2001 From: Arnaldo Carvalho de Melo Date: Tue, 16 Jul 2019 11:53:03 -0300 Subject: [PATCH] perf trace: Handle raw_syscalls:sys_enter just like the BPF_OUTPUT augmented event MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit So, we use a PERF_COUNT_SW_BPF_OUTPUT to output the augmented sys_enter payload, i.e. to output more than just the raw syscall args, and if something goes wrong when handling an unfiltered syscall, we bail out and just return 1 in the bpf program associated with raw_syscalls:sys_enter, meaning, don't filter that tracepoint, in which case what will appear in the perf ring buffer isn't the BPF_OUTPUT event, but the original raw_syscalls:sys_enter event with its normal payload. Now that we're switching to using a bpf_tail_call + BPF_MAP_TYPE_PROG_ARRAY we're going to use this in the common case, so a bug where raw_syscalls:sys_enter wasn't being handled by trace__sys_enter() surfaced and for that case, instead of using the strace-like augmenter (trace__sys_enter()), we continued to use the normal generic tracepoint handler: (gdb) p evsel $2 = (struct perf_evsel *) 0xc03e40 (gdb) p evsel->name $3 = 0xbc56c0 "raw_syscalls:sys_enter" (gdb) p ((struct perf_evsel *) 0xc03e40)->name $4 = 0xbc56c0 "raw_syscalls:sys_enter" (gdb) p ((struct perf_evsel *) 0xc03e40)->handler $5 = (void *) 0x495eb3 This resulted in this: 0.027 raw_syscalls:sys_enter:NR 12 (0, 7fcfcac64c9b, 4d, 7fcfcac64c9b, 7fcfcac6ce00, 19) ... [continued]: brk()) = 0x563b88677000 I.e. only the sys_exit tracepoint was being properly handled, but since the sys_enter went to the generic trace__event_handler() we printed it using libtraceevent's formatter instead of 'perf trace's strace-like one. Fix it by setting trace__sys_enter() as the handler for raw_syscalls:sys_enter and setup the tp_field tracepoint field accessors. Now, to test it we just make raw_syscalls:sys_enter return 1 right after checking if the pid is filtered, making it not use bpf_perf_output_event() but rather ask for the tracepoint not to be filtered and the result is the expected one: brk(NULL) = 0x556f42d6e000 I.e. raw_syscalls:sys_enter returns 1, gets handled by trace__sys_enter() and gets it combined with the raw_syscalls:sys_exit in a strace-like way. Cc: Adrian Hunter Cc: Jiri Olsa Cc: Luis Cláudio Gonçalves Cc: Namhyung Kim Link: https://lkml.kernel.org/n/tip-0mkocgk31nmy0odknegcby4z@git.kernel.org Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/builtin-trace.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c index fb8b8e78d7b5..872c9cc982a5 100644 --- a/tools/perf/builtin-trace.c +++ b/tools/perf/builtin-trace.c @@ -4128,7 +4128,22 @@ int cmd_trace(int argc, const char **argv) if (perf_evsel__init_augmented_syscall_tp(augmented, evsel) || perf_evsel__init_augmented_syscall_tp_args(augmented)) goto out; + /* + * Augmented is __augmented_syscalls__ BPF_OUTPUT event + * Above we made sure we can get from the payload the tp fields + * that we get from syscalls:sys_enter tracefs format file. + */ augmented->handler = trace__sys_enter; + /* + * Now we do the same for the *syscalls:sys_enter event so that + * if we handle it directly, i.e. if the BPF prog returns 0 so + * as not to filter it, then we'll handle it just like we would + * for the BPF_OUTPUT one: + */ + if (perf_evsel__init_augmented_syscall_tp(evsel, evsel) || + perf_evsel__init_augmented_syscall_tp_args(evsel)) + goto out; + evsel->handler = trace__sys_enter; } if (strstarts(perf_evsel__name(evsel), "syscalls:sys_exit_")) {