From 53a5d7b80032fcf48cdc5a6c96c8dc8a120b64ef Mon Sep 17 00:00:00 2001 From: Arnaldo Carvalho de Melo Date: Mon, 6 Aug 2018 09:15:18 -0300 Subject: [PATCH] perf bpf: Add bpf/stdio.h wrapper to bpf_perf_event_output function That, together with the map __bpf_output__ that is already handled by 'perf trace' to print that event's contents as strings provides a debugging facility, to show it in use, print a simple string everytime the syscalls:sys_enter_openat() syscall tracepoint is hit: # cat tools/perf/examples/bpf/hello.c #include int syscall_enter(openat)(void *args) { puts("Hello, world\n"); return 0; } license(GPL); # # perf trace -e openat,tools/perf/examples/bpf/hello.c cat /etc/passwd > /dev/null 0.016 ( ): __bpf_stdout__:Hello, world 0.018 ( 0.010 ms): cat/9079 openat(dfd: CWD, filename: /etc/ld.so.cache, flags: CLOEXEC) = 3 0.057 ( ): __bpf_stdout__:Hello, world 0.059 ( 0.011 ms): cat/9079 openat(dfd: CWD, filename: /lib64/libc.so.6, flags: CLOEXEC) = 3 0.417 ( ): __bpf_stdout__:Hello, world 0.419 ( 0.009 ms): cat/9079 openat(dfd: CWD, filename: /etc/passwd) = 3 # This is part of an ongoing experimentation on making eBPF scripts as consumed by perf to be as concise as possible and using familiar concepts such as stdio.h functions, that end up just wrapping the existing BPF functions, trying to hide as much boilerplate as possible while using just conventions and C preprocessor tricks. Cc: Adrian Hunter Cc: David Ahern Cc: Jiri Olsa Cc: Namhyung Kim Cc: Wang Nan Link: https://lkml.kernel.org/n/tip-4tiaqlx5crf0fwpe7a6j84x7@git.kernel.org Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/examples/bpf/hello.c | 9 +++++++++ tools/perf/include/bpf/stdio.h | 19 +++++++++++++++++++ 2 files changed, 28 insertions(+) create mode 100644 tools/perf/examples/bpf/hello.c create mode 100644 tools/perf/include/bpf/stdio.h diff --git a/tools/perf/examples/bpf/hello.c b/tools/perf/examples/bpf/hello.c new file mode 100644 index 000000000000..cf3c2fdc7f79 --- /dev/null +++ b/tools/perf/examples/bpf/hello.c @@ -0,0 +1,9 @@ +#include + +int syscall_enter(openat)(void *args) +{ + puts("Hello, world\n"); + return 0; +} + +license(GPL); diff --git a/tools/perf/include/bpf/stdio.h b/tools/perf/include/bpf/stdio.h new file mode 100644 index 000000000000..2899cb7bfed8 --- /dev/null +++ b/tools/perf/include/bpf/stdio.h @@ -0,0 +1,19 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include + +struct bpf_map SEC("maps") __bpf_stdout__ = { + .type = BPF_MAP_TYPE_PERF_EVENT_ARRAY, + .key_size = sizeof(int), + .value_size = sizeof(u32), + .max_entries = __NR_CPUS__, +}; + +static int (*perf_event_output)(void *, struct bpf_map *, int, void *, unsigned long) = + (void *)BPF_FUNC_perf_event_output; + +#define puts(from) \ + ({ const int __len = sizeof(from); \ + char __from[__len] = from; \ + perf_event_output(args, &__bpf_stdout__, BPF_F_CURRENT_CPU, \ + &__from, __len & (sizeof(from) - 1)); })