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selftests/bpf: add custom SEC() handling selftest
Add a selftest validating various aspects of libbpf's handling of custom SEC() handlers. It also demonstrates how libraries can ensure very early callbacks registration and unregistration using __attribute__((constructor))/__attribute__((destructor)) functions. Reviewed-by: Alan Maguire <alan.maguire@oracle.com> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
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‎tools/testing/selftests/bpf/prog_tests/custom_sec_handlers.c‎

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// SPDX-License-Identifier: GPL-2.0
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/* Copyright (c) 2022 Facebook */
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#include <test_progs.h>
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#include "test_custom_sec_handlers.skel.h"
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#define COOKIE_ABC1 1
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#define COOKIE_ABC2 2
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#define COOKIE_CUSTOM 3
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#define COOKIE_FALLBACK 4
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#define COOKIE_KPROBE 5
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static int custom_setup_prog(struct bpf_program *prog, long cookie)
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{
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if (cookie == COOKIE_ABC1)
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bpf_program__set_autoload(prog, false);
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return 0;
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}
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static int custom_prepare_load_prog(struct bpf_program *prog,
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struct bpf_prog_load_opts *opts, long cookie)
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{
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if (cookie == COOKIE_FALLBACK)
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opts->prog_flags |= BPF_F_SLEEPABLE;
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else if (cookie == COOKIE_ABC1)
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ASSERT_FALSE(true, "unexpected preload for abc");
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return 0;
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}
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static int custom_attach_prog(const struct bpf_program *prog, long cookie,
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struct bpf_link **link)
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{
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switch (cookie) {
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case COOKIE_ABC2:
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*link = bpf_program__attach_raw_tracepoint(prog, "sys_enter");
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return libbpf_get_error(*link);
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case COOKIE_CUSTOM:
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*link = bpf_program__attach_tracepoint(prog, "syscalls", "sys_enter_nanosleep");
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return libbpf_get_error(*link);
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case COOKIE_KPROBE:
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case COOKIE_FALLBACK:
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/* no auto-attach for SEC("xyz") and SEC("kprobe") */
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*link = NULL;
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return 0;
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default:
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ASSERT_FALSE(true, "unexpected cookie");
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return -EINVAL;
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}
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}
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static int abc1_id;
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static int abc2_id;
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static int custom_id;
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static int fallback_id;
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static int kprobe_id;
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__attribute__((constructor))
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static void register_sec_handlers(void)
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{
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LIBBPF_OPTS(libbpf_prog_handler_opts, abc1_opts,
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.cookie = COOKIE_ABC1,
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.prog_setup_fn = custom_setup_prog,
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.prog_prepare_load_fn = custom_prepare_load_prog,
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.prog_attach_fn = NULL,
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);
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LIBBPF_OPTS(libbpf_prog_handler_opts, abc2_opts,
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.cookie = COOKIE_ABC2,
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.prog_setup_fn = custom_setup_prog,
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.prog_prepare_load_fn = custom_prepare_load_prog,
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.prog_attach_fn = custom_attach_prog,
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);
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LIBBPF_OPTS(libbpf_prog_handler_opts, custom_opts,
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.cookie = COOKIE_CUSTOM,
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.prog_setup_fn = NULL,
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.prog_prepare_load_fn = NULL,
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.prog_attach_fn = custom_attach_prog,
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);
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abc1_id = libbpf_register_prog_handler("abc", BPF_PROG_TYPE_RAW_TRACEPOINT, 0, &abc1_opts);
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abc2_id = libbpf_register_prog_handler("abc/", BPF_PROG_TYPE_RAW_TRACEPOINT, 0, &abc2_opts);
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custom_id = libbpf_register_prog_handler("custom+", BPF_PROG_TYPE_TRACEPOINT, 0, &custom_opts);
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}
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__attribute__((destructor))
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static void unregister_sec_handlers(void)
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{
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libbpf_unregister_prog_handler(abc1_id);
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libbpf_unregister_prog_handler(abc2_id);
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libbpf_unregister_prog_handler(custom_id);
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}
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void test_custom_sec_handlers(void)
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{
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LIBBPF_OPTS(libbpf_prog_handler_opts, opts,
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.prog_setup_fn = custom_setup_prog,
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.prog_prepare_load_fn = custom_prepare_load_prog,
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.prog_attach_fn = custom_attach_prog,
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);
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struct test_custom_sec_handlers* skel;
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int err;
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ASSERT_GT(abc1_id, 0, "abc1_id");
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ASSERT_GT(abc2_id, 0, "abc2_id");
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ASSERT_GT(custom_id, 0, "custom_id");
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/* override libbpf's handle of SEC("kprobe/...") but also allow pure
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* SEC("kprobe") due to "kprobe+" specifier. Register it as
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* TRACEPOINT, just for fun.
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*/
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opts.cookie = COOKIE_KPROBE;
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kprobe_id = libbpf_register_prog_handler("kprobe+", BPF_PROG_TYPE_TRACEPOINT, 0, &opts);
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/* fallback treats everything as BPF_PROG_TYPE_SYSCALL program to test
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* setting custom BPF_F_SLEEPABLE bit in preload handler
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*/
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opts.cookie = COOKIE_FALLBACK;
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fallback_id = libbpf_register_prog_handler(NULL, BPF_PROG_TYPE_SYSCALL, 0, &opts);
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if (!ASSERT_GT(fallback_id, 0, "fallback_id") /* || !ASSERT_GT(kprobe_id, 0, "kprobe_id")*/) {
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if (fallback_id > 0)
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libbpf_unregister_prog_handler(fallback_id);
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if (kprobe_id > 0)
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libbpf_unregister_prog_handler(kprobe_id);
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return;
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}
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/* open skeleton and validate assumptions */
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skel = test_custom_sec_handlers__open();
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if (!ASSERT_OK_PTR(skel, "skel_open"))
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goto cleanup;
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ASSERT_EQ(bpf_program__type(skel->progs.abc1), BPF_PROG_TYPE_RAW_TRACEPOINT, "abc1_type");
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ASSERT_FALSE(bpf_program__autoload(skel->progs.abc1), "abc1_autoload");
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ASSERT_EQ(bpf_program__type(skel->progs.abc2), BPF_PROG_TYPE_RAW_TRACEPOINT, "abc2_type");
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ASSERT_EQ(bpf_program__type(skel->progs.custom1), BPF_PROG_TYPE_TRACEPOINT, "custom1_type");
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ASSERT_EQ(bpf_program__type(skel->progs.custom2), BPF_PROG_TYPE_TRACEPOINT, "custom2_type");
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ASSERT_EQ(bpf_program__type(skel->progs.kprobe1), BPF_PROG_TYPE_TRACEPOINT, "kprobe1_type");
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ASSERT_EQ(bpf_program__type(skel->progs.xyz), BPF_PROG_TYPE_SYSCALL, "xyz_type");
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skel->rodata->my_pid = getpid();
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/* now attempt to load everything */
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err = test_custom_sec_handlers__load(skel);
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if (!ASSERT_OK(err, "skel_load"))
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goto cleanup;
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/* now try to auto-attach everything */
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err = test_custom_sec_handlers__attach(skel);
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if (!ASSERT_OK(err, "skel_attach"))
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goto cleanup;
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skel->links.xyz = bpf_program__attach(skel->progs.kprobe1);
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ASSERT_EQ(errno, EOPNOTSUPP, "xyz_attach_err");
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ASSERT_ERR_PTR(skel->links.xyz, "xyz_attach");
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/* trigger programs */
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usleep(1);
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/* SEC("abc") is set to not auto-loaded */
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ASSERT_FALSE(skel->bss->abc1_called, "abc1_called");
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ASSERT_TRUE(skel->bss->abc2_called, "abc2_called");
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ASSERT_TRUE(skel->bss->custom1_called, "custom1_called");
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ASSERT_TRUE(skel->bss->custom2_called, "custom2_called");
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/* SEC("kprobe") shouldn't be auto-attached */
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ASSERT_FALSE(skel->bss->kprobe1_called, "kprobe1_called");
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/* SEC("xyz") shouldn't be auto-attached */
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ASSERT_FALSE(skel->bss->xyz_called, "xyz_called");
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cleanup:
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test_custom_sec_handlers__destroy(skel);
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ASSERT_OK(libbpf_unregister_prog_handler(fallback_id), "unregister_fallback");
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ASSERT_OK(libbpf_unregister_prog_handler(kprobe_id), "unregister_kprobe");
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}

‎tools/testing/selftests/bpf/progs/test_custom_sec_handlers.c‎

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// SPDX-License-Identifier: GPL-2.0
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/* Copyright (c) 2022 Facebook */
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#include "vmlinux.h"
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#include <bpf/bpf_helpers.h>
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#include <bpf/bpf_tracing.h>
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const volatile int my_pid;
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bool abc1_called;
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bool abc2_called;
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bool custom1_called;
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bool custom2_called;
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bool kprobe1_called;
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bool xyz_called;
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SEC("abc")
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int abc1(void *ctx)
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{
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abc1_called = true;
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return 0;
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}
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SEC("abc/whatever")
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int abc2(void *ctx)
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{
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abc2_called = true;
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return 0;
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}
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SEC("custom")
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int custom1(void *ctx)
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{
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custom1_called = true;
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return 0;
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}
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SEC("custom/something")
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int custom2(void *ctx)
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{
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custom2_called = true;
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return 0;
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}
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SEC("kprobe")
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int kprobe1(void *ctx)
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{
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kprobe1_called = true;
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return 0;
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}
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SEC("xyz/blah")
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int xyz(void *ctx)
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{
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int whatever;
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/* use sleepable helper, custom handler should set sleepable flag */
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bpf_copy_from_user(&whatever, sizeof(whatever), NULL);
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xyz_called = true;
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return 0;
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}
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char _license[] SEC("license") = "GPL";

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