On Sat, 30 May 2026 11:07:54 -0400 Steven Rostedt <[email protected]> wrote:
> On Sat, 30 May 2026 23:14:27 +0900 > Masami Hiramatsu (Google) <[email protected]> wrote: > > > Thanks, and Sashiko reviewed this. > > > > https://sashiko.dev/#/patchset/20260529110442.0967a64c%40fedora > > > > I think both comments are valid, especially, second one is important. > > Hmm, comment below. > > > > > BTW, I updated probes/fixes. Could you also update this and rebase > > on probes/fixes branch? > > > > I'm working on the nesting and container_of support patches which > > are on top of this. > > OK, I'll make sure to use your probes branch. Which one should I use? your > probes/for-next or probes/urgent? Ah, probes/fixes. (I think I need to update probes/for-next to rebase on it) > > As for sashiko's comments: > > > commit c8393ea9936934c16ba2881d9e7b3cce86c678ff > > Author: Steven Rostedt <[email protected]> > > [PATCH v7] tracing/eprobes: Allow use of BTF names to dereference pointers > > This commit introduces syntax to allow event probes to typecast pointer > > fields to a structure using BTF. This enables dereferencing structures > > using BTF names rather than having to manually calculate offsets. > > > diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c > > > index 39f040c863e85..0e87409a44033 100644 > > > --- a/kernel/trace/trace_probe.c > > > +++ b/kernel/trace/trace_probe.c > > [ ... ] > > > @@ -640,7 +673,7 @@ static int parse_btf_arg(char *varname, > > > int i, is_ptr, ret; > > > u32 tid; > > > > > > - if (WARN_ON_ONCE(!ctx->funcname)) > > > + if (WARN_ON_ONCE(!ctx->funcname && !(ctx->flags & TPARG_FL_TEVENT))) > > > return -EINVAL; > > > > > > is_ptr = split_next_field(varname, &field, ctx); > > > @@ -653,6 +686,16 @@ static int parse_btf_arg(char *varname, > > > return -EOPNOTSUPP; > > > } > > > > > > + if (ctx->flags & TPARG_FL_TEVENT) { > > > + ret = parse_trace_event(varname, code, ctx); > > > + if (ret < 0) > > > + return ret; > > > Does this silently drop the error on parsing failure? > > If parse_trace_event() fails and returns -EINVAL, it appears this path > > returns the error without logging it. > > Unlike parse_probe_vars(), which explicitly logs the failure when > > parse_trace_event() fails, this path bypasses the log. Could this make > > it difficult to debug invalid typecast expressions since nothing is written > > to tracing/error_log? > > Hmm, I guess I can put an error log here, as this is a unique path. Yeah, just adding trace_probe_log_err(ctx->offset, BAD_VAR) seems OK. > > > > + if (WARN_ON_ONCE(!(ctx->flags & TPARG_FL_TYPECAST))) > > > + return -EINVAL; > > > + type = ctx->last_struct; > > > + goto found_type; > > > + } > > > + > > > if (ctx->flags & TPARG_FL_RETURN && !strcmp(varname, "$retval")) { > > > code->op = FETCH_OP_RETVAL; > > [ ... ] > > > @@ -758,7 +802,71 @@ static int parse_btf_bitfield(struct fetch_insn > > > **pcode, > > > return 0; > > > } > > > > > > -#else > > > +static int query_btf_struct(const char *sname, struct > > > traceprobe_parse_context *ctx) > > [ ... ] > > > +static int handle_typecast(char *arg, struct fetch_insn **pcode, > > > + struct fetch_insn *end, > > > + struct traceprobe_parse_context *ctx) > > > +{ > > > + char *tmp; > > > + int ret; > > > + > > > + /* Currently this only works for eprobes */ > > > + if (!(ctx->flags & TPARG_FL_TEVENT)) { > > > + trace_probe_log_err(ctx->offset, TYPECAST_NOT_EVENT); > > > + return -EINVAL; > > > + } > > > + > > > + tmp = strchr(arg, ')'); > > > + if (!tmp) { > > > + trace_probe_log_err(ctx->offset + strlen(arg), > > > + DEREF_OPEN_BRACE); > > > + return -EINVAL; > > > + } > > > + *tmp = '\0'; > > > + ret = query_btf_struct(arg + 1, ctx); > > > + *tmp = ')'; > > > + > > > + if (ret < 0) { > > > + trace_probe_log_err(ctx->offset + 1, NO_PTR_STRCT); > > > + ret = -EINVAL; > > > + goto out_put; > > > + } > > > + > > > + ctx->flags |= TPARG_FL_TYPECAST; > > > + tmp++; > > > + > > > + ctx->offset += tmp - arg; > > > + ret = parse_btf_arg(tmp, pcode, end, ctx); > > > + ctx->flags &= ~TPARG_FL_TYPECAST; > > > + ctx->last_struct = NULL; > > > +out_put: > > > + btf_put(ctx->struct_btf); > > > Does this prematurely release the BTF struct reference? > > If TPARG_FL_TYPECAST is unset here and ctx->struct_btf is put, won't > > later steps in traceprobe_parse_probe_arg_body() (like > > find_fetch_type_from_btf_type()) fail to properly infer struct field sizes? > > When ctx_btf(ctx) is called later without TPARG_FL_TYPECAST set, it > > will evaluate to ctx->btf (which is NULL for eprobes). > > Could this potentially lead to silent defaults, such as 64-bit reads for > > smaller fields, or fail to inject pointer dereferences for string fields, > > while also leaving ctx->last_type pointing to a prematurely released BTF > > object? > > Does this mean we need to set ctx->last_type to NULL here too? No, since the member we refer can be different from unsigned long. When we don't have ":type" suffix, we use BTF type information to decide appropriate type. > > Because everything above is pretty much the expected behavior. The put is > *not* premature. The last_struct and struct_btf are both set to NULL. I > guess the only thing missing is to reset last_type as well. No, as I explained, the last_type is used to determine the member type when user does not specify the ":type" suffix. So, what we need to do is deferring the btf_put(struct_btf) as below: (no build test yet.) diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c index adaa1e4fbdd6..9a73c49e22df 100644 --- a/kernel/trace/trace_probe.c +++ b/kernel/trace/trace_probe.c @@ -538,6 +538,10 @@ static void clear_btf_context(struct traceprobe_parse_context *ctx) ctx->params = NULL; ctx->nr_params = 0; } + if (ctx->struct_btf) { + btf_put(ctx->struct_btf); + ctx->struct_btf = NULL; + } } /* Return 1 if the field separator is arrow operator ('->') */ @@ -802,22 +806,18 @@ static int parse_btf_bitfield(struct fetch_insn **pcode, static int query_btf_struct(const char *sname, struct traceprobe_parse_context *ctx) { + struct btf *btf = NULL; int id; - if (!ctx->struct_btf) { - struct btf *btf; - - id = bpf_find_btf_id(sname, BTF_KIND_STRUCT, &btf); - if (id < 0) - return id; - ctx->struct_btf = btf; - } else { - id = btf_find_by_name_kind(ctx->struct_btf, sname, BTF_KIND_STRUCT); - if (id < 0) - return id; + if (ctx->struct_btf) { + btf_put(ctx->struct_btf); + ctx->struct_btf = NULL; } - ctx->last_struct = btf_type_by_id(ctx->struct_btf, id); + id = bpf_find_btf_id(sname, BTF_KIND_STRUCT, &btf); + if (id < 0) + return id; + ctx->struct_btf = btf; return 0; } @@ -846,8 +846,7 @@ static int handle_typecast(char *arg, struct fetch_insn **pcode, if (ret < 0) { trace_probe_log_err(ctx->offset + 1, NO_PTR_STRCT); - ret = -EINVAL; - goto out_put; + return ret; } ctx->flags |= TPARG_FL_TYPECAST; @@ -857,9 +856,6 @@ static int handle_typecast(char *arg, struct fetch_insn **pcode, ret = parse_btf_arg(tmp, pcode, end, ctx); ctx->flags &= ~TPARG_FL_TYPECAST; ctx->last_struct = NULL; -out_put: - btf_put(ctx->struct_btf); - ctx->struct_btf = NULL; return ret; } Thanks! -- Masami Hiramatsu (Google) <[email protected]>
