From: Andrii Nakryiko <andriin@fb.com>
To: <bpf@vger.kernel.org>, <netdev@vger.kernel.org>, <ast@fb.com>,
<daniel@iogearbox.net>, <yhs@fb.com>
Cc: <andrii.nakryiko@gmail.com>, <kernel-team@fb.com>,
Andrii Nakryiko <andriin@fb.com>,
Alexei Starovoitov <ast@kernel.org>
Subject: [PATCH v2 bpf-next] libbpf: support .text sub-calls relocations
Date: Wed, 15 Jan 2020 11:08:56 -0800 [thread overview]
Message-ID: <20200115190856.2391325-1-andriin@fb.com> (raw)
The LLVM patch https://reviews.llvm.org/D72197 makes LLVM emit function call
relocations within the same section. This includes a default .text section,
which contains any BPF sub-programs. This wasn't the case before and so libbpf
was able to get a way with slightly simpler handling of subprogram call
relocations.
This patch adds support for .text section relocations. It needs to ensure
correct order of relocations, so does two passes:
- first, relocate .text instructions, if there are any relocations in it;
- then process all the other programs and copy over patched .text instructions
for all sub-program calls.
v1->v2:
- break early once .text program is processed.
Cc: Yonghong Song <yhs@fb.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
---
tools/lib/bpf/libbpf.c | 29 ++++++++++++++++++++++-------
1 file changed, 22 insertions(+), 7 deletions(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 0c229f00a67e..23868883477f 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -4692,13 +4692,7 @@ bpf_program__reloc_text(struct bpf_program *prog, struct bpf_object *obj,
size_t new_cnt;
int err;
- if (prog->idx == obj->efile.text_shndx) {
- pr_warn("relo in .text insn %d into off %d (insn #%d)\n",
- relo->insn_idx, relo->sym_off, relo->sym_off / 8);
- return -LIBBPF_ERRNO__RELOC;
- }
-
- if (prog->main_prog_cnt == 0) {
+ if (prog->idx != obj->efile.text_shndx && prog->main_prog_cnt == 0) {
text = bpf_object__find_prog_by_idx(obj, obj->efile.text_shndx);
if (!text) {
pr_warn("no .text section found yet relo into text exist\n");
@@ -4728,6 +4722,7 @@ bpf_program__reloc_text(struct bpf_program *prog, struct bpf_object *obj,
text->insns_cnt, text->section_name,
prog->section_name);
}
+
insn = &prog->insns[relo->insn_idx];
insn->imm += relo->sym_off / 8 + prog->main_prog_cnt - relo->insn_idx;
return 0;
@@ -4807,8 +4802,28 @@ bpf_object__relocate(struct bpf_object *obj, const char *targ_btf_path)
return err;
}
}
+ /* ensure .text is relocated first, as it's going to be copied as-is
+ * later for sub-program calls
+ */
+ for (i = 0; i < obj->nr_programs; i++) {
+ prog = &obj->programs[i];
+ if (prog->idx != obj->efile.text_shndx)
+ continue;
+
+ err = bpf_program__relocate(prog, obj);
+ if (err) {
+ pr_warn("failed to relocate '%s'\n", prog->section_name);
+ return err;
+ }
+ break;
+ }
+ /* now relocate everything but .text, which by now is relocated
+ * properly, so we can copy raw sub-program instructions as is safely
+ */
for (i = 0; i < obj->nr_programs; i++) {
prog = &obj->programs[i];
+ if (prog->idx == obj->efile.text_shndx)
+ continue;
err = bpf_program__relocate(prog, obj);
if (err) {
--
2.17.1
next reply other threads:[~2020-01-15 19:09 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-15 19:08 Andrii Nakryiko [this message]
2020-01-15 19:29 ` [PATCH v2 bpf-next] libbpf: support .text sub-calls relocations Yonghong Song
2020-01-15 20:05 ` Alexei Starovoitov
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