On 6/5/21 4:10 AM, Jiri Olsa wrote:
Adding support to load tracing program with new BPF_F_MULTI_FUNC flag,
that allows the program to be loaded without specific function to be
attached to.
The verifier assumes the program is using all (6) available arguments
Is this a verifier failure or it is due to the check in the
beginning of function arch_prepare_bpf_trampoline()?
/* x86-64 supports up to 6 arguments. 7+ can be added in the
future */
if (nr_args > 6)
return -ENOTSUPP;
If it is indeed due to arch_prepare_bpf_trampoline() maybe we
can improve it instead of specially processing the first argument
"ip" in quite some places?
as unsigned long values. We can't add extra ip argument at this time,
because JIT on x86 would fail to process this function. Instead we
allow to access extra first 'ip' argument in btf_ctx_access.
Such program will be allowed to be attached to multiple functions
in following patches.
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
---
include/linux/bpf.h | 1 +
include/uapi/linux/bpf.h | 7 +++++++
kernel/bpf/btf.c | 5 +++++
kernel/bpf/syscall.c | 35 +++++++++++++++++++++++++++++-----
kernel/bpf/verifier.c | 3 ++-
tools/include/uapi/linux/bpf.h | 7 +++++++
6 files changed, 52 insertions(+), 6 deletions(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 6cbf3c81c650..23221e0e8d3c 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -845,6 +845,7 @@ struct bpf_prog_aux {
bool sleepable;
bool tail_call_reachable;
struct hlist_node tramp_hlist;
+ bool multi_func;
Move this field right after "tail_call_reachable"?
/* BTF_KIND_FUNC_PROTO for valid attach_btf_id */
const struct btf_type *attach_func_proto;
/* function name for valid attach_btf_id */
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 2c1ba70abbf1..ad9340fb14d4 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1109,6 +1109,13 @@ enum bpf_link_type {
*/
#define BPF_F_SLEEPABLE (1U << 4)
+/* If BPF_F_MULTI_FUNC is used in BPF_PROG_LOAD command, the verifier does
+ * not expect BTF ID for the program, instead it assumes it's function
+ * with 6 u64 arguments. No trampoline is created for the program. Such
+ * program can be attached to multiple functions.
+ */
+#define BPF_F_MULTI_FUNC (1U << 5)
+
/* When BPF ldimm64's insn[0].src_reg != 0 then this can have
* the following extensions:
*
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index a6e39c5ea0bf..c233aaa6a709 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -4679,6 +4679,11 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
args++;
nr_args--;
}
+ if (prog->aux->multi_func) {
+ if (arg == 0)
+ return true;
+ arg--;
Some comments in the above to mention like "the first 'ip' argument
is omitted" will be good.
+ }
if (arg > nr_args) {
bpf_log(log, "func '%s' doesn't have %d-th argument\n",
[...]
