From 6ccc18a9a17a1189b8b157176ce4a58c458c9eee Mon Sep 17 00:00:00 2001 From: Arnaldo Carvalho de Melo Date: Tue, 21 Aug 2018 11:14:15 -0300 Subject: perf trace: Make the augmented_syscalls filter out the tracepoint event When we attach a eBPF object to a tracepoint, if we return 1, then that tracepoint will be stored in the perf's ring buffer. In the augmented_syscalls.c case we want to just attach and _override_ the tracepoint payload with an augmented, extended one. In this example, tools/perf/examples/bpf/augmented_syscalls.c, we are attaching to the 'openat' syscall, and adding, after the syscalls:sys_enter_openat usual payload as defined by /sys/kernel/debug/tracing/events/syscalls/sys_enter_openat/format, a snapshot of its sole pointer arg: # grep 'field:.*\*' /sys/kernel/debug/tracing/events/syscalls/sys_enter_openat/format field:const char * filename; offset:24; size:8; signed:0; # For now this is not being considered, the next csets will make use of it, but as this is overriding the syscall tracepoint enter, we don't want that event appearing on the ring buffer, just our synthesized one. Before: # perf trace -e ~acme/git/perf/tools/perf/examples/bpf/augmented_syscalls.c,openat cat /etc/passwd > /dev/null 0.000 ( ): __augmented_syscalls__:dfd: CWD, filename: /etc/ld.so.cache, flags: CLOEXEC 0.006 ( ): syscalls:sys_enter_openat:dfd: CWD, filename: , flags: CLOEXEC 0.007 ( 0.004 ms): cat/24044 openat(dfd: CWD, filename: 0x216dda8, flags: CLOEXEC ) = 3 0.028 ( ): __augmented_syscalls__:dfd: CWD, filename: /lib64/libc.so.6, flags: CLOEXEC 0.030 ( ): syscalls:sys_enter_openat:dfd: CWD, filename: , flags: CLOEXEC 0.031 ( 0.006 ms): cat/24044 openat(dfd: CWD, filename: 0x2375ce0, flags: CLOEXEC ) = 3 0.291 ( ): __augmented_syscalls__:dfd: CWD, filename: /etc/passwd 0.293 ( ): syscalls:sys_enter_openat:dfd: CWD, filename: 0.294 ( 0.004 ms): cat/24044 openat(dfd: CWD, filename: 0x637db06b ) = 3 # After: # perf trace -e ~acme/git/perf/tools/perf/examples/bpf/augmented_syscalls.c,openat cat /etc/passwd > /dev/null 0.000 ( ): __augmented_syscalls__:dfd: CWD, filename: 0x9c6a1da8, flags: CLOEXEC 0.005 ( 0.015 ms): cat/27341 openat(dfd: CWD, filename: 0x9c6a1da8, flags: CLOEXEC ) = 3 0.040 ( ): __augmented_syscalls__:dfd: CWD, filename: 0x9c8a9ce0, flags: CLOEXEC 0.041 ( 0.006 ms): cat/27341 openat(dfd: CWD, filename: 0x9c8a9ce0, flags: CLOEXEC ) = 3 0.294 ( ): __augmented_syscalls__:dfd: CWD, filename: 0x482a706b 0.296 ( 0.067 ms): cat/27341 openat(dfd: CWD, filename: 0x482a706b ) = 3 # Now lets replace that __augmented_syscalls__ name with the syscall name, using: # grep 'field:.*syscall_nr' /sys/kernel/debug/tracing/events/syscalls/sys_enter_openat/format field:int __syscall_nr; offset:8; size:4; signed:1; # That the synthesized payload has exactly where the syscall enter tracepoint puts it. Cc: Adrian Hunter Cc: David Ahern Cc: Jiri Olsa Cc: Namhyung Kim Cc: Wang Nan Link: https://lkml.kernel.org/n/tip-og4r9k87mzp9hv7el046idmd@git.kernel.org Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/examples/bpf/augmented_syscalls.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'tools/perf/examples/bpf/augmented_syscalls.c') diff --git a/tools/perf/examples/bpf/augmented_syscalls.c b/tools/perf/examples/bpf/augmented_syscalls.c index 69a31386d8cd..10e7997ab481 100644 --- a/tools/perf/examples/bpf/augmented_syscalls.c +++ b/tools/perf/examples/bpf/augmented_syscalls.c @@ -49,7 +49,7 @@ int syscall_enter(openat)(struct syscall_enter_openat_args *args) probe_read_str(&augmented_args.filename, sizeof(augmented_args.filename), args->filename_ptr); perf_event_output(args, &__augmented_syscalls__, BPF_F_CURRENT_CPU, &augmented_args, sizeof(augmented_args)); - return 1; + return 0; } license(GPL); -- cgit v1.2.3-59-g8ed1b