cregit-Linux how code gets into the kernel

Release 4.9 samples/bpf/lathist_kern.c

Directory: samples/bpf
/* Copyright (c) 2013-2015 PLUMgrid, http://plumgrid.com
 * Copyright (c) 2015 BMW Car IT GmbH
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of version 2 of the GNU General Public
 * License as published by the Free Software Foundation.
 */
#include <linux/version.h>
#include <linux/ptrace.h>
#include <uapi/linux/bpf.h>
#include "bpf_helpers.h"


#define MAX_ENTRIES	20

#define MAX_CPU		4

/* We need to stick to static allocated memory (an array instead of
 * hash table) because managing dynamic memory from the
 * trace_preempt_[on|off] tracepoints hooks is not supported.
 */

struct bpf_map_def SEC("maps") my_map = {
	.type = BPF_MAP_TYPE_ARRAY,
	.key_size = sizeof(int),
	.value_size = sizeof(u64),
	.max_entries = MAX_CPU,
};

SEC("kprobe/trace_preempt_off")

int bpf_prog1(struct pt_regs *ctx) { int cpu = bpf_get_smp_processor_id(); u64 *ts = bpf_map_lookup_elem(&my_map, &cpu); if (ts) *ts = bpf_ktime_get_ns(); return 0; }

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daniel wagnerdaniel wagner42100.00%1100.00%
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static unsigned int log2(unsigned int v) { unsigned int r; unsigned int shift; r = (v > 0xFFFF) << 4; v >>= r; shift = (v > 0xFF) << 3; v >>= shift; r |= shift; shift = (v > 0xF) << 2; v >>= shift; r |= shift; shift = (v > 0x3) << 1; v >>= shift; r |= shift; r |= (v >> 1); return r; }

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daniel wagnerdaniel wagner98100.00%1100.00%
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static unsigned int log2l(unsigned long v) { unsigned int hi = v >> 32; if (hi) return log2(hi) + 32; else return log2(v); }

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daniel wagnerdaniel wagner38100.00%1100.00%
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struct bpf_map_def SEC("maps") my_lat = { .type = BPF_MAP_TYPE_ARRAY, .key_size = sizeof(int), .value_size = sizeof(long), .max_entries = MAX_CPU * MAX_ENTRIES, }; SEC("kprobe/trace_preempt_on")
int bpf_prog2(struct pt_regs *ctx) { u64 *ts, cur_ts, delta; int key, cpu; long *val; cpu = bpf_get_smp_processor_id(); ts = bpf_map_lookup_elem(&my_map, &cpu); if (!ts) return 0; cur_ts = bpf_ktime_get_ns(); delta = log2l(cur_ts - *ts); if (delta > MAX_ENTRIES - 1) delta = MAX_ENTRIES - 1; key = cpu * MAX_ENTRIES + delta; val = bpf_map_lookup_elem(&my_lat, &key); if (val) __sync_fetch_and_add((long *)val, 1); return 0; }

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daniel wagnerdaniel wagner117100.00%1100.00%
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char _license[] SEC("license") = "GPL"; u32 _version SEC("version") = LINUX_VERSION_CODE;

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daniel wagnerdaniel wagner418100.00%1100.00%
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Directory: samples/bpf