forked from luck/tmp_suning_uos_patched
6ccc18a9a1
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 <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-og4r9k87mzp9hv7el046idmd@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
56 lines
1.8 KiB
C
56 lines
1.8 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Augment the openat syscall with the contents of the filename pointer argument.
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*
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* Test it with:
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*
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* perf trace -e tools/perf/examples/bpf/augmented_syscalls.c cat /etc/passwd > /dev/null
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*
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* It'll catch some openat syscalls related to the dynamic linked and
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* the last one should be the one for '/etc/passwd'.
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*
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* This matches what is marshalled into the raw_syscall:sys_enter payload
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* expected by the 'perf trace' beautifiers, and can be used by them unmodified,
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* which will be done as that feature is implemented in the next csets, for now
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* it will appear in a dump done by the default tracepoint handler in 'perf trace',
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* that uses bpf_output__fprintf() to just dump those contents, as done with
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* the bpf-output event associated with the __bpf_output__ map declared in
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* tools/perf/include/bpf/stdio.h.
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*/
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#include <stdio.h>
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struct bpf_map SEC("maps") __augmented_syscalls__ = {
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.type = BPF_MAP_TYPE_PERF_EVENT_ARRAY,
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.key_size = sizeof(int),
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.value_size = sizeof(u32),
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.max_entries = __NR_CPUS__,
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};
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struct syscall_enter_openat_args {
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unsigned long long common_tp_fields;
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long syscall_nr;
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long dfd;
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char *filename_ptr;
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long flags;
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long mode;
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};
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struct augmented_enter_openat_args {
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struct syscall_enter_openat_args args;
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char filename[64];
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};
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int syscall_enter(openat)(struct syscall_enter_openat_args *args)
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{
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struct augmented_enter_openat_args augmented_args;
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probe_read(&augmented_args.args, sizeof(augmented_args.args), args);
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probe_read_str(&augmented_args.filename, sizeof(augmented_args.filename), args->filename_ptr);
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perf_event_output(args, &__augmented_syscalls__, BPF_F_CURRENT_CPU,
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&augmented_args, sizeof(augmented_args));
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return 0;
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}
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license(GPL);
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