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authorWang Nan <wangnan0@huawei.com>2015-07-01 05:14:05 +0300
committerArnaldo Carvalho de Melo <acme@redhat.com>2015-08-07 16:16:58 +0300
commit8a47a6c522c0593a977069b0b1e5a0725ca0e32e (patch)
treea3cb881b72e4e4954a69da91111acaa9148915f9 /tools/lib
parent52d3352e79815307521bef6121dba00b6c3477c6 (diff)
downloadlinux-8a47a6c522c0593a977069b0b1e5a0725ca0e32e.tar.xz
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: Wang Nan <wangnan0@huawei.com> Acked-by: Alexei 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.com Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Diffstat (limited to 'tools/lib')
-rw-r--r--tools/lib/bpf/libbpf.c52
1 files changed, 52 insertions, 0 deletions
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 54b48de3df78..94f966008887 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -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: