Commit 9173cac3 authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
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libbpf: Support .text sub-calls relocations 

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: default avatarAndrii Nakryiko <andriin@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarYonghong Song <yhs@fb.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200115190856.2391325-1-andriin@fb.com
parent 5640a771

tools/lib/bpf/libbpf.c

+22 −7
Original line number Diff line number Diff line
@@ -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) {

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