Add support for BPF_FRK_EXISTS relocation kind to detect existence of
captured field in a destination BTF, allowing conditional logic to
handle incompatible differences between kernels.
Also introduce opt-in relaxed CO-RE relocation handling option, which
makes libbpf emit warning for failed relocations, but proceed with other
relocations. Instruction, for which relocation failed, is patched with
(u32)-1 value.
Signed-off-by: Andrii Nakryiko <andriin@xxxxxx>
---
tools/lib/bpf/libbpf.c | 74 +++++++++++++++++++++++++++++++++---------
tools/lib/bpf/libbpf.h | 4 ++-
2 files changed, 61 insertions(+), 17 deletions(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index db3308b91806..bebd9eb352ee 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -249,6 +249,7 @@ struct bpf_object {
bool loaded;
bool has_pseudo_calls;
+ bool relaxed_core_relocs;
/*
* Information when doing elf related work. Only valid if fd
@@ -2771,26 +2772,54 @@ static int bpf_core_spec_match(struct bpf_core_spec *local_spec,
/*
* Patch relocatable BPF instruction.
- * Expected insn->imm value is provided for validation, as well as the new
- * relocated value.
+ *
+ * Patched value is determined by relocation kind and target specification.
+ * For field existence relocation target spec will be NULL if field is not
+ * found.
+ * Expected insn->imm value is determined using relocation kind and local
+ * spec, and is checked before patching instruction. If actual insn->imm value
+ * is wrong, bail out with error.
*
* Currently three kinds of BPF instructions are supported:
* 1. rX = <imm> (assignment with immediate operand);
* 2. rX += <imm> (arithmetic operations with immediate operand);
- * 3. *(rX) = <imm> (indirect memory assignment with immediate operand).
- *
- * If actual insn->imm value is wrong, bail out.
*/
-static int bpf_core_reloc_insn(struct bpf_program *prog, int insn_off,
- __u32 orig_off, __u32 new_off)
+static int bpf_core_reloc_insn(struct bpf_program *prog,
+ const struct bpf_field_reloc *relo,
+ const struct bpf_core_spec *local_spec,
+ const struct bpf_core_spec *targ_spec)
{
+ __u32 orig_val, new_val;
struct bpf_insn *insn;
int insn_idx;
__u8 class;
- if (insn_off % sizeof(struct bpf_insn))
+ if (relo->insn_off % sizeof(struct bpf_insn))
return -EINVAL;
- insn_idx = insn_off / sizeof(struct bpf_insn);
+ insn_idx = relo->insn_off / sizeof(struct bpf_insn);
+
+ switch (relo->kind) {
+ case BPF_FRK_BYTE_OFFSET:
+ orig_val = local_spec->offset;
+ if (targ_spec) {
+ new_val = targ_spec->offset;
+ } else {
+ pr_warning("prog '%s': patching insn #%d w/ failed reloc, imm %d -> %d\n",
+ bpf_program__title(prog, false), insn_idx,
+ orig_val, -1);
+ new_val = (__u32)-1;
+ }
+ break;
+ case BPF_FRK_EXISTS:
+ orig_val = 1; /* can't generate EXISTS relo w/o local field */
+ new_val = targ_spec ? 1 : 0;
+ break;
+ default:
+ pr_warning("prog '%s': unknown relo %d at insn #%d'\n",
+ bpf_program__title(prog, false),
+ relo->kind, insn_idx);
+ return -EINVAL;
+ }
insn = &prog->insns[insn_idx];
class = BPF_CLASS(insn->code);
@@ -2798,12 +2827,12 @@ static int bpf_core_reloc_insn(struct bpf_program *prog, int insn_off,
if (class == BPF_ALU || class == BPF_ALU64) {
if (BPF_SRC(insn->code) != BPF_K)
return -EINVAL;
- if (insn->imm != orig_off)
+ if (insn->imm != orig_val)
return -EINVAL;
- insn->imm = new_off;
+ insn->imm = new_val;
pr_debug("prog '%s': patched insn #%d (ALU/ALU64) imm %d -> %d\n",
bpf_program__title(prog, false),
- insn_idx, orig_off, new_off);
+ insn_idx, orig_val, new_val);
} else {
pr_warning("prog '%s': trying to relocate unrecognized insn #%d, code:%x, src:%x, dst:%x, off:%x, imm:%x\n",
bpf_program__title(prog, false),
@@ -2811,6 +2840,7 @@ static int bpf_core_reloc_insn(struct bpf_program *prog, int insn_off,
insn->off, insn->imm);
return -EINVAL;
}
+
return 0;
}
@@ -3087,15 +3117,26 @@ static int bpf_core_reloc_field(struct bpf_program *prog,
cand_ids->data[j++] = cand_spec.spec[0].type_id;
}
- cand_ids->len = j;
- if (cand_ids->len == 0) {
+ /*
+ * For BPF_FRK_EXISTS relo or when relaxed CO-RE reloc mode is
+ * requested, it's expected that we might not find any candidates.
+ * In this case, if field wasn't found in any candidate, the list of
+ * candidates shouldn't change at all, we'll just handle relocating
+ * appropriately, depending on relo's kind.
+ */
+ if (j > 0)
+ cand_ids->len = j;
+
+ if (j == 0 && !prog->obj->relaxed_core_relocs &&
+ relo->kind != BPF_FRK_EXISTS) {
pr_warning("prog '%s': relo #%d: no matching targets found for [%d] %s + %s\n",
prog_name, relo_idx, local_id, local_name, spec_str);
return -ESRCH;
}
- err = bpf_core_reloc_insn(prog, relo->insn_off,
- local_spec.offset, targ_spec.offset);
+ /* bpf_core_reloc_insn should know how to handle missing targ_spec */
+ err = bpf_core_reloc_insn(prog, relo, &local_spec,
+ j ? &targ_spec : NULL);
if (err) {
pr_warning("prog '%s': relo #%d: failed to patch insn at offset %d: %d\n",
prog_name, relo_idx, relo->insn_off, err);
@@ -3587,6 +3628,7 @@ __bpf_object__open(const char *path, const void *obj_buf, size_t obj_buf_sz,
if (IS_ERR(obj))
return obj;
+ obj->relaxed_core_relocs = OPTS_GET(opts, relaxed_core_relocs, false);
relaxed_maps = OPTS_GET(opts, relaxed_maps, false);
CHECK_ERR(bpf_object__elf_init(obj), err, out);
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 667e6853e51f..53ce212764e0 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -96,8 +96,10 @@ struct bpf_object_open_opts {
const char *object_name;
/* parse map definitions non-strictly, allowing extra attributes/data */
bool relaxed_maps;
+ /* process CO-RE relocations non-strictly, allowing them to fail */
+ bool relaxed_core_relocs;
};
-#define bpf_object_open_opts__last_field relaxed_maps
+#define bpf_object_open_opts__last_field relaxed_core_relocs
LIBBPF_API struct bpf_object *bpf_object__open(const char *path);
LIBBPF_API struct bpf_object *
--
2.17.1
