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Subject[PATCH v3 linux-trace 8/8] samples: bpf: simple kprobe example
Date
the logic of the example is similar to tracex2, but syscall 'write' statistics
is capturead from kprobe placed at sys_write function instead of through
syscall instrumentation.
Also tracex4_kern.c has a different way of doing log2 in C.
Note, unlike tracepoint and syscall programs, kprobe programs receive
'struct pt_regs' as an input. It's responsibility of the program author
or higher level dynamic tracing tool to match registers to function arguments.
Since pt_regs are architecture dependent, programs are also arch dependent,
unlike tracepoint/syscalls programs which are universal.

Usage:
$ sudo tracex4
2216443+0 records in
2216442+0 records out
1134818304 bytes (1.1 GB) copied, 2.00746 s, 565 MB/s

kprobe sys_write() stats
byte_size : count distribution
1 -> 1 : 0 | |
2 -> 3 : 0 | |
4 -> 7 : 0 | |
8 -> 15 : 0 | |
16 -> 31 : 0 | |
32 -> 63 : 0 | |
64 -> 127 : 1 | |
128 -> 255 : 0 | |
256 -> 511 : 0 | |
512 -> 1023 : 2214734 |************************************* |

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
---
samples/bpf/Makefile | 4 +++
samples/bpf/bpf_load.c | 3 ++
samples/bpf/tracex4_kern.c | 36 +++++++++++++++++++
samples/bpf/tracex4_user.c | 83 ++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 126 insertions(+)
create mode 100644 samples/bpf/tracex4_kern.c
create mode 100644 samples/bpf/tracex4_user.c

diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index da0efd8032ab..22c7a38f3f95 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -10,6 +10,7 @@ hostprogs-y += dropmon
hostprogs-y += tracex1
hostprogs-y += tracex2
hostprogs-y += tracex3
+hostprogs-y += tracex4

dropmon-objs := dropmon.o libbpf.o
test_verifier-objs := test_verifier.o libbpf.o
@@ -20,6 +21,7 @@ sockex2-objs := bpf_load.o libbpf.o sockex2_user.o
tracex1-objs := bpf_load.o libbpf.o tracex1_user.o
tracex2-objs := bpf_load.o libbpf.o tracex2_user.o
tracex3-objs := bpf_load.o libbpf.o tracex3_user.o
+tracex4-objs := bpf_load.o libbpf.o tracex4_user.o

# Tell kbuild to always build the programs
always := $(hostprogs-y)
@@ -28,6 +30,7 @@ always += sockex2_kern.o
always += tracex1_kern.o
always += tracex2_kern.o
always += tracex3_kern.o
+always += tracex4_kern.o

HOSTCFLAGS += -I$(objtree)/usr/include

@@ -37,6 +40,7 @@ HOSTLOADLIBES_sockex2 += -lelf
HOSTLOADLIBES_tracex1 += -lelf
HOSTLOADLIBES_tracex2 += -lelf
HOSTLOADLIBES_tracex3 += -lelf
+HOSTLOADLIBES_tracex4 += -lelf

# point this to your LLVM backend with bpf support
LLC=$(srctree)/tools/bpf/llvm/bld/Debug+Asserts/bin/llc
diff --git a/samples/bpf/bpf_load.c b/samples/bpf/bpf_load.c
index 2aece65963e4..2206b49df625 100644
--- a/samples/bpf/bpf_load.c
+++ b/samples/bpf/bpf_load.c
@@ -32,6 +32,7 @@ int prog_cnt;
static int load_and_attach(const char *event, struct bpf_insn *prog, int size)
{
bool is_socket = strncmp(event, "socket", 6) == 0;
+ bool is_kprobe = strncmp(event, "events/kprobes/", 15) == 0;
enum bpf_prog_type prog_type;
char path[256] = DEBUGFS;
char buf[32];
@@ -45,6 +46,8 @@ static int load_and_attach(const char *event, struct bpf_insn *prog, int size)

if (is_socket)
prog_type = BPF_PROG_TYPE_SOCKET_FILTER;
+ else if (is_kprobe)
+ prog_type = BPF_PROG_TYPE_KPROBE;
else
prog_type = BPF_PROG_TYPE_TRACEPOINT;

diff --git a/samples/bpf/tracex4_kern.c b/samples/bpf/tracex4_kern.c
new file mode 100644
index 000000000000..9646f9e43417
--- /dev/null
+++ b/samples/bpf/tracex4_kern.c
@@ -0,0 +1,36 @@
+#include <linux/skbuff.h>
+#include <linux/netdevice.h>
+#include <uapi/linux/bpf.h>
+#include <trace/bpf_trace.h>
+#include "bpf_helpers.h"
+
+static unsigned int log2l(unsigned long long n)
+{
+#define S(k) if (n >= (1ull << k)) { i += k; n >>= k; }
+ int i = -(n == 0);
+ S(32); S(16); S(8); S(4); S(2); S(1);
+ return i;
+#undef S
+}
+
+struct bpf_map_def SEC("maps") my_hist_map = {
+ .type = BPF_MAP_TYPE_ARRAY,
+ .key_size = sizeof(u32),
+ .value_size = sizeof(long),
+ .max_entries = 64,
+};
+
+SEC("events/kprobes/sys_write")
+int bpf_prog4(struct pt_regs *regs)
+{
+ long write_size = regs->dx; /* $rdx contains 3rd argument to a function */
+ long init_val = 1;
+ void *value;
+ u32 index = log2l(write_size);
+
+ value = bpf_map_lookup_elem(&my_hist_map, &index);
+ if (value)
+ __sync_fetch_and_add((long *)value, 1);
+ return 0;
+}
+char _license[] SEC("license") = "GPL";
diff --git a/samples/bpf/tracex4_user.c b/samples/bpf/tracex4_user.c
new file mode 100644
index 000000000000..741206127768
--- /dev/null
+++ b/samples/bpf/tracex4_user.c
@@ -0,0 +1,83 @@
+#include <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <signal.h>
+#include <linux/bpf.h>
+#include "libbpf.h"
+#include "bpf_load.h"
+
+#define MAX_INDEX 64
+#define MAX_STARS 38
+
+static void stars(char *str, long val, long max, int width)
+{
+ int i;
+
+ for (i = 0; i < (width * val / max) - 1 && i < width - 1; i++)
+ str[i] = '*';
+ if (val > max)
+ str[i - 1] = '+';
+ str[i] = '\0';
+}
+
+static void print_hist(int fd)
+{
+ int key;
+ long value;
+ long data[MAX_INDEX] = {};
+ char starstr[MAX_STARS];
+ int i;
+ int max_ind = -1;
+ long max_value = 0;
+
+ for (key = 0; key < MAX_INDEX; key++) {
+ bpf_lookup_elem(fd, &key, &value);
+ data[key] = value;
+ if (value && key > max_ind)
+ max_ind = key;
+ if (value > max_value)
+ max_value = value;
+ }
+
+ printf("\n kprobe sys_write() stats\n");
+ printf(" byte_size : count distribution\n");
+ for (i = 1; i <= max_ind + 1; i++) {
+ stars(starstr, data[i - 1], max_value, MAX_STARS);
+ printf("%8ld -> %-8ld : %-8ld |%-*s|\n",
+ (1l << i) >> 1, (1l << i) - 1, data[i - 1],
+ MAX_STARS, starstr);
+ }
+}
+static void int_exit(int sig)
+{
+ print_hist(map_fd[0]);
+ exit(0);
+}
+
+int main(int ac, char **argv)
+{
+ char filename[256];
+ FILE *f;
+ int i;
+
+ snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
+
+ signal(SIGINT, int_exit);
+
+ i = system("echo 'p:sys_write sys_write' > /sys/kernel/debug/tracing/kprobe_events");
+ (void) i;
+
+ /* start 'dd' in the background to have plenty of 'write' syscalls */
+ f = popen("dd if=/dev/zero of=/dev/null count=5000000", "r");
+ (void) f;
+
+ if (load_bpf_file(filename)) {
+ printf("%s", bpf_log_buf);
+ return 1;
+ }
+
+ sleep(2);
+ kill(0, SIGINT); /* send Ctrl-C to self and to 'dd' */
+
+ return 0;
+}
--
1.7.9.5


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