From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DE9FD1E5B70; Wed, 10 Jun 2026 00:51:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781052717; cv=none; b=FnOgIZVr9uErIDNPFpvEubw1QnB2zbbMWqHe0RpCDzyu7KMk7OkW59Z6kh74+i0rFT2KQzc6wudsiAMwUH3eH9wX83tBu0aND7t3skqGMyV4uZYXXTrCjBTYhHA4jjgaETGQZj91kD6Z0PSCBW55zr7BhsL4yKm6XKiskWRUoos= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781052717; c=relaxed/simple; bh=YAYS7SYX5EYChmD4cMxkAFIgcqcuhauGz0UZOBzsfCQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=GJoknj0XcS85fp4DkJ4ahQ4V36rwZr6bsBc8kEBbKXAX4Rk9heMCvnAdGvH4IL4C56GV63FgEjfh8pyXvlqaYJy/QlbnU4cFrteXctBPVCq6pLnmDKhfVMIIuSwObENo2Hm25veeKPQ3HFdjSNYu/H8S54NUvtkdRIWwqil0fe0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=SRsRz5Tz; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="SRsRz5Tz" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 935EF1F00893; Wed, 10 Jun 2026 00:51:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781052715; bh=vHyzK7th7ig2jGo2NU2kB/RUneIkmWgue1vkgkAVYbQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=SRsRz5TzHWGPE3hGAB6vt8DbuY7dJDOo0rd8mhaJyRB+Dz6QpP5GCmtPnT2kMa7Sh mwC3loBiwyFHnklObfryQHeG7cn9q36I0MZZvQztbtmaR4r/9EHbisnox3qBS9R94w CCATnj2sb8S6Ntbn+aF7aFRRei6MrZI/Clqim854FefGy270ISucN+OftBC6GAksmI dgrYWDkMXkUjKEEgZ8yBqNool76y3s+ai/H6M3OozMAF+/rkJMOlWCU6eURXkwgC4U fb3Ukm03XyxxLhC+z9lzbUAOQ6zo+Mzl/F3U6hBrYezZkaSBXtyIepjFW6wmI3jgbJ saWGU8E/U+1Cg== From: "Masami Hiramatsu (Google)" To: Steven Rostedt , Mathieu Desnoyers Cc: Jonathan Corbet , Shuah Khan , Masami Hiramatsu , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [RFC PATCH v2 3/7] tracing/probes: Support nested typecast Date: Wed, 10 Jun 2026 09:51:50 +0900 Message-ID: <178105271020.21760.7206043226962935811.stgit@devnote2> X-Mailer: git-send-email 2.43.0 In-Reply-To: <178105268094.21760.13668249930524377840.stgit@devnote2> References: <178105268094.21760.13668249930524377840.stgit@devnote2> User-Agent: StGit/0.19 Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit From: Masami Hiramatsu (Google) When we hit an open parenthesis right after typecast closing parenthesis, it means we have nested typecast. This allows us to typecast a generic data member in a structure to a pointer to another structure. For example, to cast a DATA_MEMBER of VAR structure to STRUCT pointer and get MEMBER value. (STRUCT)(VAR->DATA_MEMBER)->MEMBER Also, we can nest typecast. (STRUCT1)((STRUCT2)$ARG->FIELD2)->FIELD1 Currently the max nest level is limited to 3. Signed-off-by: Masami Hiramatsu (Google) --- Changes in v2: - Fix to skip "->" after closing parenthetsis. --- Documentation/trace/eprobetrace.rst | 2 + Documentation/trace/fprobetrace.rst | 2 + Documentation/trace/kprobetrace.rst | 2 + kernel/trace/trace.c | 1 kernel/trace/trace_probe.c | 76 ++++++++++++++++++++++++++++++++--- kernel/trace/trace_probe.h | 7 +++ 6 files changed, 82 insertions(+), 8 deletions(-) diff --git a/Documentation/trace/eprobetrace.rst b/Documentation/trace/eprobetrace.rst index fe3602540569..cd0b4aa7f896 100644 --- a/Documentation/trace/eprobetrace.rst +++ b/Documentation/trace/eprobetrace.rst @@ -50,6 +50,8 @@ Synopsis of eprobe_events a pointer to STRUCT and then derference the pointer defined by ->MEMBER. Note that when this is used, the FIELD name does not need to be prefixed with a '$'. + (STRUCT)(FETCHARG)->MEMBER[->MEMBER] : typecast can nest, so the above can + also be used with another FETCHARG instead of FIELD. Types ----- diff --git a/Documentation/trace/fprobetrace.rst b/Documentation/trace/fprobetrace.rst index 7435ded2d66d..6b8bb27bb62d 100644 --- a/Documentation/trace/fprobetrace.rst +++ b/Documentation/trace/fprobetrace.rst @@ -60,6 +60,8 @@ Synopsis of fprobe-events (STRUCT)FIELD->MEMBER[->MEMBER] : If BTF is supported, typecast FIELD to a pointer to STRUCT and then derference the pointer defined by ->MEMBER. + (STRUCT)(FETCHARG)->MEMBER[->MEMBER] : typecast can nest, so the above can + also be used with another FETCHARG instead of FIELD. (\*1) This is available only when BTF is enabled. (\*2) only for the probe on function entry (offs == 0). Note, this argument access diff --git a/Documentation/trace/kprobetrace.rst b/Documentation/trace/kprobetrace.rst index f73614997d52..c4382765d5b2 100644 --- a/Documentation/trace/kprobetrace.rst +++ b/Documentation/trace/kprobetrace.rst @@ -65,6 +65,8 @@ Synopsis of kprobe_events a pointer to STRUCT and then derference the pointer defined by ->MEMBER. Note that this is available only when the probe is on function entry. + (STRUCT)(FETCHARG)->MEMBER[->MEMBER] : typecast can nest, so the above can + also be used with another FETCHARG instead of FIELD. (\*1) only for the probe on function entry (offs == 0). Note, this argument access is best effort, because depending on the argument type, it may be passed on diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index aa93e7b01146..4f70318918c2 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -4326,6 +4326,7 @@ static const char readme_msg[] = "\t $stack, $stack, $retval, $comm, $arg,\n" #ifdef CONFIG_PROBE_EVENTS_BTF_ARGS "\t [(structname)][->field[->field|.field...]],\n" + "\t [(structname)](fetcharg)->field[->field|.field...],\n" #endif #else "\t $stack, $stack, $retval, $comm,\n" diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c index 9158f1f22a62..dba73aaa8ade 100644 --- a/kernel/trace/trace_probe.c +++ b/kernel/trace/trace_probe.c @@ -832,10 +832,35 @@ static int query_btf_struct(const char *sname, struct traceprobe_parse_context * return 0; } +/* Find the matching closing parenthesis for a given opening parenthesis. */ +static char *find_matched_close_paren(char *s) +{ + char *p = s; + int count = 0; + + while (*p) { + if (*p == '(') + count++; + else if (*p == ')') { + if (--count == 0) + return p; + } + p++; + } + return NULL; +} + +static int +parse_probe_arg(char *arg, const struct fetch_type *type, + struct fetch_insn **pcode, struct fetch_insn *end, + struct traceprobe_parse_context *ctx); + static int handle_typecast(char *arg, struct fetch_insn **pcode, struct fetch_insn *end, struct traceprobe_parse_context *ctx) { + int orig_offset = ctx->offset; + bool nested = false; char *tmp; int ret; @@ -852,19 +877,56 @@ static int handle_typecast(char *arg, struct fetch_insn **pcode, DEREF_OPEN_BRACE); return -EINVAL; } - *tmp = '\0'; - ret = query_btf_struct(arg + 1, ctx); - *tmp = ')'; + *tmp++ = '\0'; + + /* Handle the nested structure like (STRUCT)(VAR->FIELD)->... */ + if (*tmp == '(') { + char *close = find_matched_close_paren(tmp); + + ctx->offset += tmp - arg; + if (!close) { + trace_probe_log_err(ctx->offset, DEREF_OPEN_BRACE); + return -EINVAL; + } + /* We expect a field access for typecast */ + if (close[1] != '-' || close[2] != '>') { + trace_probe_log_err(ctx->offset + close - tmp + 1, + TYPECAST_REQ_FIELD); + return -EINVAL; + } + ctx->nested_level++; + if (ctx->nested_level > TRACEPROBE_MAX_NESTED_LEVEL) { + trace_probe_log_err(ctx->offset, TOO_MANY_NESTED); + return -E2BIG; + } + *close = '\0'; + + ctx->offset += 1; /* for the '(' */ + /* We need to parse the nested one */ + ret = parse_probe_arg(tmp + 1, find_fetch_type(NULL, ctx->flags), + pcode, end, ctx); + if (ret < 0) + return ret; + ctx->nested_level--; + clear_struct_btf(ctx); + + tmp = close + 3;/* Skip "->" after closing parenthesis */ + nested = true; + } + + ret = query_btf_struct(arg + 1, ctx); if (ret < 0) { trace_probe_log_err(ctx->offset + 1, NO_PTR_STRCT); return -EINVAL; } - tmp++; - - ctx->offset += tmp - arg; - ret = parse_btf_arg(tmp, pcode, end, ctx); + ctx->offset = orig_offset + tmp - arg; + /* If it is nested, tmp points to the field name. */ + if (nested) + ret = parse_btf_field(tmp, ctx->last_struct, pcode, end, ctx); + else + ret = parse_btf_arg(tmp, pcode, end, ctx); return ret; } diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h index 883938a74aee..982d32a5df8b 100644 --- a/kernel/trace/trace_probe.h +++ b/kernel/trace/trace_probe.h @@ -435,8 +435,11 @@ struct traceprobe_parse_context { struct trace_probe *tp; unsigned int flags; int offset; + int nested_level; }; +#define TRACEPROBE_MAX_NESTED_LEVEL 3 + extern int traceprobe_parse_probe_arg(struct trace_probe *tp, int i, const char *argv, struct traceprobe_parse_context *ctx); @@ -571,7 +574,9 @@ extern int traceprobe_define_arg_fields(struct trace_event_call *event_call, C(TOO_MANY_ARGS, "Too many arguments are specified"), \ C(TOO_MANY_EARGS, "Too many entry arguments specified"), \ C(EVENT_TOO_BIG, "Event too big (too many fields?)"), \ - C(TYPECAST_NOT_EVENT, "Typecasts are only for eprobe fields"), + C(TYPECAST_NOT_EVENT, "Typecasts are only for eprobe fields"), \ + C(TYPECAST_REQ_FIELD, "Typecast requires a field access"), \ + C(TOO_MANY_NESTED, "Too many nested typecasts/dereferences"), #undef C #define C(a, b) TP_ERR_##a