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libbpf: Prepare light skeleton for the kernel.

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Prepare light skeleton to be used in the kernel module and in the user space.
The look and feel of lskel.h is mostly the same with the difference that for
user space the skel->rodata is the same pointer before and after skel_load
operation, while in the kernel the skel->rodata after skel_open and the
skel->rodata after skel_load are different pointers.
Typical usage of skeleton remains the same for kernel and user space:
skel = my_bpf__open();
skel->rodata->my_global_var = init_val;
err = my_bpf__load(skel);
err = my_bpf__attach(skel);
// access skel->rodata->my_global_var;
// access skel->bss->another_var;

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220209232001.27490-3-alexei.starovoitov@gmail.com
This commit is contained in:
Alexei Starovoitov
2022-02-09 15:19:58 -08:00
committed by Andrii Nakryiko
parent 7593fc7a85
commit 0d6262ad0a
2 changed files with 179 additions and 21 deletions
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15
src/gen_loader.c
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@@ -1043,18 +1043,27 @@ void bpf_gen__map_update_elem(struct bpf_gen *gen, int map_idx, void *pvalue,
value = add_data(gen, pvalue, value_size);
key = add_data(gen, &zero, sizeof(zero));
/* if (map_desc[map_idx].initial_value)
* copy_from_user(value, initial_value, value_size);
/* if (map_desc[map_idx].initial_value) {
* if (ctx->flags & BPF_SKEL_KERNEL)
* bpf_probe_read_kernel(value, value_size, initial_value);
* else
* bpf_copy_from_user(value, value_size, initial_value);
* }
*/
emit(gen, BPF_LDX_MEM(BPF_DW, BPF_REG_3, BPF_REG_6,
sizeof(struct bpf_loader_ctx) +
sizeof(struct bpf_map_desc) * map_idx +
offsetof(struct bpf_map_desc, initial_value)));
emit(gen, BPF_JMP_IMM(BPF_JEQ, BPF_REG_3, 0, 4));
emit(gen, BPF_JMP_IMM(BPF_JEQ, BPF_REG_3, 0, 8));
emit2(gen, BPF_LD_IMM64_RAW_FULL(BPF_REG_1, BPF_PSEUDO_MAP_IDX_VALUE,
0, 0, 0, value));
emit(gen, BPF_MOV64_IMM(BPF_REG_2, value_size));
emit(gen, BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_6,
offsetof(struct bpf_loader_ctx, flags)));
emit(gen, BPF_JMP_IMM(BPF_JSET, BPF_REG_0, BPF_SKEL_KERNEL, 2));
emit(gen, BPF_EMIT_CALL(BPF_FUNC_copy_from_user));
emit(gen, BPF_JMP_IMM(BPF_JA, 0, 0, 1));
emit(gen, BPF_EMIT_CALL(BPF_FUNC_probe_read_kernel));
map_update_attr = add_data(gen, &attr, attr_size);
move_blob2blob(gen, attr_field(map_update_attr, map_fd), 4,