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bpftool: Add an example for struct_ops map and shadow type.

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The example in bpftool-gen.8 explains how to use the pointer of the shadow
type to change the value of a field of a struct_ops map.

Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Quentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/bpf/20240229064523.2091270-5-thinker.li@gmail.com
This commit is contained in:
Kui-Feng Lee 2024-02-28 22:45:22 -08:00 committed by Andrii Nakryiko
parent a7b0fa352e
commit f2e81192e0
1 changed files with 52 additions and 6 deletions
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58
tools/bpf/bpftool/Documentation/bpftool-gen.rst
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@ -257,18 +257,48 @@ EXAMPLES
return 0;
}
This is example BPF application with two BPF programs and a mix of BPF maps
and global variables. Source code is split across two source code files.
**$ cat example3.bpf.c**
::
#include <linux/ptrace.h>
#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>
/* This header file is provided by the bpf_testmod module. */
#include "bpf_testmod.h"
int test_2_result = 0;
/* bpf_Testmod.ko calls this function, passing a "4"
* and testmod_map->data.
*/
SEC("struct_ops/test_2")
void BPF_PROG(test_2, int a, int b)
{
test_2_result = a + b;
}
SEC(".struct_ops")
struct bpf_testmod_ops testmod_map = {
.test_2 = (void *)test_2,
.data = 0x1,
};
This is example BPF application with three BPF programs and a mix of BPF
maps and global variables. Source code is split across three source code
files.
**$ clang --target=bpf -g example1.bpf.c -o example1.bpf.o**
**$ clang --target=bpf -g example2.bpf.c -o example2.bpf.o**
**$ bpftool gen object example.bpf.o example1.bpf.o example2.bpf.o**
**$ clang --target=bpf -g example3.bpf.c -o example3.bpf.o**
This set of commands compiles *example1.bpf.c* and *example2.bpf.c*
individually and then statically links respective object files into the final
BPF ELF object file *example.bpf.o*.
**$ bpftool gen object example.bpf.o example1.bpf.o example2.bpf.o example3.bpf.o**
This set of commands compiles *example1.bpf.c*, *example2.bpf.c* and
*example3.bpf.c* individually and then statically links respective object
files into the final BPF ELF object file *example.bpf.o*.
**$ bpftool gen skeleton example.bpf.o name example | tee example.skel.h**
@ -291,7 +321,15 @@ BPF ELF object file *example.bpf.o*.
struct bpf_map *data;
struct bpf_map *bss;
struct bpf_map *my_map;
struct bpf_map *testmod_map;
} maps;
struct {
struct example__testmod_map__bpf_testmod_ops {
const struct bpf_program *test_1;
const struct bpf_program *test_2;
int data;
} *testmod_map;
} struct_ops;
struct {
struct bpf_program *handle_sys_enter;
struct bpf_program *handle_sys_exit;
@ -304,6 +342,7 @@ BPF ELF object file *example.bpf.o*.
struct {
int x;
} data;
int test_2_result;
} *bss;
struct example__data {
_Bool global_flag;
@ -342,10 +381,16 @@ BPF ELF object file *example.bpf.o*.
skel->rodata->param1 = 128;
/* Change the value through the pointer of shadow type */
skel->struct_ops.testmod_map->data = 13;
err = example__load(skel);
if (err)
goto cleanup;
/* The result of the function test_2() */
printf("test_2_result: %d\n", skel->bss->test_2_result);
err = example__attach(skel);
if (err)
goto cleanup;
@ -372,6 +417,7 @@ BPF ELF object file *example.bpf.o*.
::
test_2_result: 17
my_map name: my_map
sys_enter prog FD: 8
my_static_var: 7