From: Andrii Nakryiko <andriin@fb.com>
Date: Wed, 15 Jan 2020 11:08:56 -0800
Subject: libbpf: Support .text sub-calls relocations
Patch-mainline: v5.6-rc1
Git-commit: 9173cac3b64e6785dd604f5075e6035b045a0026
References: bsc#1177028
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.
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200115190856.2391325-1-andriin@fb.com
Acked-by: Gary Lin <glin@suse.com>
---
tools/lib/bpf/libbpf.c | 29 ++++++++++++++++++++++-------
1 file changed, 22 insertions(+), 7 deletions(-)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -4693,13 +4693,7 @@ bpf_program__reloc_text(struct bpf_progr
size_t new_cnt;
int err;
- if (prog->idx == obj->efile.text_shndx) {
- pr_warning("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_warning("no .text section found yet relo into text exist\n");
@@ -4729,6 +4723,7 @@ bpf_program__reloc_text(struct bpf_progr
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;
@@ -4808,8 +4803,28 @@ bpf_object__relocate(struct bpf_object *
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_warning("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) {