提交 8a47a6c5 编写于 作者: W Wang Nan 提交者: Arnaldo Carvalho de Melo

bpf tools: Relocate eBPF programs

If an eBPF program accesses a map, LLVM generates a load instruction
which loads an absolute address into a register, like this:

  ld_64   r1, <MCOperand Expr:(mymap)>
  ...
  call    2

That ld_64 instruction will be recorded in relocation section.
To enable the usage of that map, relocation must be done by replacing
the immediate value by real map file descriptor so it can be found by
eBPF map functions.

This patch to the relocation work based on information collected by
patches:

'bpf tools: Collect symbol table from SHT_SYMTAB section',
'bpf tools: Collect relocation sections from SHT_REL sections'
and
'bpf tools: Record map accessing instructions for each program'.

For each instruction which needs relocation, it inject corresponding
file descriptor to imm field. As a part of protocol, src_reg is set to
BPF_PSEUDO_MAP_FD to notify kernel this is a map loading instruction.

This is the final part of map relocation patch. The principle of map
relocation is described in commit message of 'bpf tools: Collect symbol
table from SHT_SYMTAB section'.
Signed-off-by: NWang Nan <wangnan0@huawei.com>
Acked-by: NAlexei Starovoitov <ast@plumgrid.com>
Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David Ahern <dsahern@gmail.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kaixu Xia <xiakaixu@huawei.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1435716878-189507-18-git-send-email-wangnan0@huawei.comSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>
上级 52d3352e
......@@ -630,6 +630,56 @@ bpf_object__create_maps(struct bpf_object *obj)
return 0;
}
static int
bpf_program__relocate(struct bpf_program *prog, int *map_fds)
{
int i;
if (!prog || !prog->reloc_desc)
return 0;
for (i = 0; i < prog->nr_reloc; i++) {
int insn_idx, map_idx;
struct bpf_insn *insns = prog->insns;
insn_idx = prog->reloc_desc[i].insn_idx;
map_idx = prog->reloc_desc[i].map_idx;
if (insn_idx >= (int)prog->insns_cnt) {
pr_warning("relocation out of range: '%s'\n",
prog->section_name);
return -ERANGE;
}
insns[insn_idx].src_reg = BPF_PSEUDO_MAP_FD;
insns[insn_idx].imm = map_fds[map_idx];
}
zfree(&prog->reloc_desc);
prog->nr_reloc = 0;
return 0;
}
static int
bpf_object__relocate(struct bpf_object *obj)
{
struct bpf_program *prog;
size_t i;
int err;
for (i = 0; i < obj->nr_programs; i++) {
prog = &obj->programs[i];
err = bpf_program__relocate(prog, obj->map_fds);
if (err) {
pr_warning("failed to relocate '%s'\n",
prog->section_name);
return err;
}
}
return 0;
}
static int bpf_object__collect_reloc(struct bpf_object *obj)
{
int i, err;
......@@ -761,6 +811,8 @@ int bpf_object__load(struct bpf_object *obj)
obj->loaded = true;
if (bpf_object__create_maps(obj))
goto out;
if (bpf_object__relocate(obj))
goto out;
return 0;
out:
......
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