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There's a bug in LLVM that it can generate unneeded relocation information. See [1] and [2]. Libbpf should check the target section of a relocation symbol. This patch adds a testcase which references a global variable (BPF doesn't support global variables). Before fixing libbpf, the new test case can be loaded into kernel, the global variable acts like the first map. It is incorrect. Result: # ~/perf test BPF 37: Test BPF filter : 37.1: Test basic BPF filtering : Ok 37.2: Test BPF prologue generation : Ok 37.3: Test BPF relocation checker : FAILED! # ~/perf test -v BPF ... libbpf: loading object '[bpf_relocation_test]' from buffer libbpf: section .strtab, size 126, link 0, flags 0, type=3 libbpf: section .text, size 0, link 0, flags 6, type=1 libbpf: section .data, size 0, link 0, flags 3, type=1 libbpf: section .bss, size 0, link 0, flags 3, type=8 libbpf: section func=sys_write, size 104, link 0, flags 6, type=1 libbpf: found program func=sys_write libbpf: section .relfunc=sys_write, size 16, link 10, flags 0, type=9 libbpf: section maps, size 16, link 0, flags 3, type=1 libbpf: maps in [bpf_relocation_test]: 16 bytes libbpf: section license, size 4, link 0, flags 3, type=1 libbpf: license of [bpf_relocation_test] is GPL libbpf: section version, size 4, link 0, flags 3, type=1 libbpf: kernel version of [bpf_relocation_test] is 40400 libbpf: section .symtab, size 144, link 1, flags 0, type=2 libbpf: map 0 is "my_table" libbpf: collecting relocating info for: 'func=sys_write' libbpf: relocation: insn_idx=7 Success unexpectedly: libbpf error when dealing with relocation test child finished with -1 ---- end ---- Test BPF filter subtest 2: FAILED! [1] https://llvm.org/bugs/show_bug.cgi?id=26243 [2] https://patchwork.ozlabs.org/patch/571385/ Signed-off-by: Wang Nan <wangnan0@huawei.com> Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: "David S. Miller" <davem@davemloft.net> Cc: Alexei Starovoitov <ast@kernel.org> Cc: Brendan Gregg <brendan.d.gregg@gmail.com> Cc: Daniel Borkmann <daniel@iogearbox.net> Cc: He Kuang <hekuang@huawei.com> Cc: Jiri Olsa <jolsa@kernel.org> Cc: Li Zefan <lizefan@huawei.com> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> Cc: Namhyung Kim <namhyung@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Will Deacon <will.deacon@arm.com> Cc: pi3orama@163.com Link: http://lkml.kernel.org/r/1453715801-7732-2-git-send-email-wangnan0@huawei.com Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
50 lines
1.3 KiB
C
50 lines
1.3 KiB
C
/*
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* bpf-script-test-relocation.c
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* Test BPF loader checking relocation
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*/
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#ifndef LINUX_VERSION_CODE
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# error Need LINUX_VERSION_CODE
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# error Example: for 4.2 kernel, put 'clang-opt="-DLINUX_VERSION_CODE=0x40200" into llvm section of ~/.perfconfig'
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#endif
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#define BPF_ANY 0
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#define BPF_MAP_TYPE_ARRAY 2
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#define BPF_FUNC_map_lookup_elem 1
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#define BPF_FUNC_map_update_elem 2
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static void *(*bpf_map_lookup_elem)(void *map, void *key) =
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(void *) BPF_FUNC_map_lookup_elem;
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static void *(*bpf_map_update_elem)(void *map, void *key, void *value, int flags) =
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(void *) BPF_FUNC_map_update_elem;
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struct bpf_map_def {
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unsigned int type;
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unsigned int key_size;
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unsigned int value_size;
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unsigned int max_entries;
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};
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#define SEC(NAME) __attribute__((section(NAME), used))
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struct bpf_map_def SEC("maps") my_table = {
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.type = BPF_MAP_TYPE_ARRAY,
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.key_size = sizeof(int),
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.value_size = sizeof(int),
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.max_entries = 1,
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};
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int this_is_a_global_val;
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SEC("func=sys_write")
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int bpf_func__sys_write(void *ctx)
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{
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int key = 0;
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int value = 0;
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/*
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* Incorrect relocation. Should not allow this program be
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* loaded into kernel.
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*/
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bpf_map_update_elem(&this_is_a_global_val, &key, &value, 0);
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return 0;
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}
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char _license[] SEC("license") = "GPL";
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int _version SEC("version") = LINUX_VERSION_CODE;
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