On Tue, 1 Sep 2026 00:06:16 +0900
"Masami Hiramatsu (Google)" <[email protected]> wrote:
> diff --git a/kernel/trace/trace_btf.h b/kernel/trace/trace_btf.h
> index 4bc44bc261e6..4bd26bceae23 100644
> --- a/kernel/trace/trace_btf.h
> +++ b/kernel/trace/trace_btf.h
> @@ -8,4 +8,5 @@ const struct btf_param *btf_get_func_param(const struct
> btf_type *func_proto,
> const struct btf_member *btf_find_struct_member(struct btf *btf,
> const struct btf_type *type,
> const char *member_name,
> - u32 *anon_offset);
> + u32 *anon_offset,
> + const struct btf_type
> **member_type);
> diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
> index c4163904ba74..ce2a7bb00d28 100644
> --- a/kernel/trace/trace_probe.c
> +++ b/kernel/trace/trace_probe.c
> @@ -625,6 +625,7 @@ static int get_bitoffset_of_field(char **pfieldname,
> const struct btf_type **pty
> {
> const struct btf_type *type = *ptype;
> const struct btf_member *field;
> + const struct btf_type *mtype = NULL;
Why initialize mtype to NULL?
> struct btf *btf = ctx_btf(ctx);
> char *fieldname = *pfieldname;
> int bitoffs = 0;
> @@ -640,7 +641,7 @@ static int get_bitoffset_of_field(char **pfieldname,
> const struct btf_type **pty
>
> anon_offs = 0;
> field = btf_find_struct_member(btf, type, fieldname,
> - &anon_offs);
> + &anon_offs, &mtype);
If mtype is not set here, then field would be either an error or NULL.
> if (IS_ERR(field)) {
> trace_probe_log_err(ctx->offset, BAD_BTF_TID);
> return PTR_ERR(field);
If field is an error or NULL, it exits out early.
> @@ -653,7 +654,7 @@ static int get_bitoffset_of_field(char **pfieldname,
> const struct btf_type **pty
> bitoffs += anon_offs;
>
> /* Accumulate the bit-offsets of the dot-connected fields */
> - if (btf_type_kflag(type)) {
> + if (btf_type_kflag(mtype)) {
mtype should be guaranteed as set here (maybe set to NULL, but set regardless)
Now, if btf_find_struct_member() did not set mtype, because this is in a
loop, in a second iteration, mtype would be stale.
So either set it to NULL at the top of the loop, or don't set it at all.
Or am I missing something?
-- Steve
> bitoffs += BTF_MEMBER_BIT_OFFSET(field->offset);
> ctx->last_bitsize =
> BTF_MEMBER_BITFIELD_SIZE(field->offset);
> } else {
> @@ -661,11 +662,11 @@ static int get_bitoffset_of_field(char **pfieldname,
> const struct btf_type **pty
> ctx->last_bitsize = 0;
> }
>
> - type = btf_type_skip_modifiers(btf, field->type, NULL);
> - if (!type) {
> - trace_probe_log_err(ctx->offset, BAD_BTF_TID);
> - return -EINVAL;
> - }
> + type = btf_type_skip_modifiers(btf, field->type, NULL);
> + if (!type) {
> + trace_probe_log_err(ctx->offset, BAD_BTF_TID);
> + return -EINVAL;
> + }
>
> if (next)
> ctx->offset += next - fieldname;
