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 B05951F0E25; Wed, 10 Jun 2026 00:52:14 +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=1781052735; cv=none; b=AsQqrasygSYeaa4FPsGvjl4dtslA392Ly0d3d78XG5yoMr44M/7cRIFgz6Dv8wQnrU/RYlp0dmuUOZ449YHGt7lZHd98QBgq9rU0DxCqD4x096trTQUN4GoZYNGFTq9/KXxmPrUNIqZNXqoFOzyIbcX23DkNPuQe8biFtK81ATE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781052735; c=relaxed/simple; bh=Fn6NFeVl+8I2Lt+Te4HJEOhim318pM42fs0mIl3ydgA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=TpgZRkcsYZKcJmM9UdA+XYldTeEOV6LByaX/GDo8eaPchMyeeK+vI44n+IELuBX4+uGYGxFA9hAzfJf7gV7q+aSjLkS2RNfa+j4Ncom6TYBzoUJhPgWsScy+/AmlRWTgQZ9wLTFE+rLGHEYD22gp9JVqPwYqxnC1HS75lGEnGQI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=fqjqqX3n; 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="fqjqqX3n" Received: by smtp.kernel.org (Postfix) with ESMTPSA id AA4151F00893; Wed, 10 Jun 2026 00:52:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781052734; bh=ZxennJuN8G9gRrbq+oG+R8TiWvbtABTeNRFAsYm0Kxs=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=fqjqqX3nDeYf8HiHxqzYHHz6ZRMp+BW3gwHFlrm/slKJKf4wzPBlE4B5PMscVSdh5 Jh1LG2qTVb+OngAdmSkimSfkpLz7yNZgmt7p+M4PnQ6+DgXORFZgpODjxhEXmfGIN9 vXo4h3OXioCNKhELx33ZUwWqsdXEOYZg5hgJLM3OkNuYMRjUg2E1HKfmUJbe49YKis qUnsiQ/6jNR5w7eOBX0zOM39FwiYmdmSiivVV1Uv/qr3rikqu3+mRZbnxNGPKuadwh pqpERJk2LPJL+Oc5Z+hIFZR3caDnwLlQgO6HfTy8Ps40khP2VohNALOKnVXH3i9xWA N2QNSWxJwD4Mw== 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 5/7] tracing/probes: Add $current variable support Date: Wed, 10 Jun 2026 09:52:10 +0900 Message-ID: <178105273050.21760.12587121915086626782.stgit@devnote2> X-Mailer: git-send-email 2.43.0 In-Reply-To: <178105268094.21760.13668249930524377840.stgit@devnote2> References: <178105268094.21760.13668249930524377840.stgit@devnote2> User-Agent: StGit/0.19 Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit From: Masami Hiramatsu (Google) Since we can use the BTF to cast value to a structure pointer type, it is useful to introduce "$current" special variable support to fetcharg. User can define a fetcharg to access current task_struct properties using BTF info. e.g. $current->cpus_ptr Signed-off-by: Masami Hiramatsu (Google) --- Changes in v2: - Support to parse $current in parse_btf_arg(). - If no typecast on $current, it automatically casted to task_struct. - Check error case if $current follows something except for "-". --- Documentation/trace/eprobetrace.rst | 1 + Documentation/trace/fprobetrace.rst | 1 + Documentation/trace/kprobetrace.rst | 1 + kernel/trace/trace.c | 2 +- kernel/trace/trace_probe.c | 29 ++++++++++++++++++++++++++++- kernel/trace/trace_probe.h | 1 + kernel/trace/trace_probe_tmpl.h | 3 +++ 7 files changed, 36 insertions(+), 2 deletions(-) diff --git a/Documentation/trace/eprobetrace.rst b/Documentation/trace/eprobetrace.rst index 680e0af43d5d..dcf92d5b4175 100644 --- a/Documentation/trace/eprobetrace.rst +++ b/Documentation/trace/eprobetrace.rst @@ -38,6 +38,7 @@ Synopsis of eprobe_events @ADDR : Fetch memory at ADDR (ADDR should be in kernel) @SYM[+|-offs] : Fetch memory at SYM +|- offs (SYM should be a data symbol) $comm : Fetch current task comm. + $current : Fetch the address of the current task_struct. +|-[u]OFFS(FETCHARG) : Fetch memory at FETCHARG +|- OFFS address.(\*3)(\*4) \IMM : Store an immediate value to the argument. NAME=FETCHARG : Set NAME as the argument name of FETCHARG. diff --git a/Documentation/trace/fprobetrace.rst b/Documentation/trace/fprobetrace.rst index 290a9e6f7491..3392cab016b3 100644 --- a/Documentation/trace/fprobetrace.rst +++ b/Documentation/trace/fprobetrace.rst @@ -50,6 +50,7 @@ Synopsis of fprobe-events $argN : Fetch the Nth function argument. (N >= 1) (\*2) $retval : Fetch return value.(\*3) $comm : Fetch current task comm. + $current : Fetch the address of the current task_struct. +|-[u]OFFS(FETCHARG) : Fetch memory at FETCHARG +|- OFFS address.(\*4)(\*5) \IMM : Store an immediate value to the argument. NAME=FETCHARG : Set NAME as the argument name of FETCHARG. diff --git a/Documentation/trace/kprobetrace.rst b/Documentation/trace/kprobetrace.rst index a62707e6a9f2..81e4fe38791d 100644 --- a/Documentation/trace/kprobetrace.rst +++ b/Documentation/trace/kprobetrace.rst @@ -53,6 +53,7 @@ Synopsis of kprobe_events $argN : Fetch the Nth function argument. (N >= 1) (\*1) $retval : Fetch return value.(\*2) $comm : Fetch current task comm. + $current : Fetch the address of the current task_struct. +|-[u]OFFS(FETCHARG) : Fetch memory at FETCHARG +|- OFFS address.(\*3)(\*4) \IMM : Store an immediate value to the argument. NAME=FETCHARG : Set NAME as the argument name of FETCHARG. diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 0e36af853199..e185a006cb08 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -4329,7 +4329,7 @@ static const char readme_msg[] = "\t [(structname[,field])](fetcharg)->field[->field|.field...],\n" #endif #else - "\t $stack, $stack, $retval, $comm,\n" + "\t $stack, $stack, $retval, $comm, $current\n" #endif "\t +|-[u](), \\imm-value, \\\"imm-string\"\n" "\t kernel return probes support: $retval, $arg, $comm\n" diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c index 726be9782775..4bdccd9bd7d1 100644 --- a/kernel/trace/trace_probe.c +++ b/kernel/trace/trace_probe.c @@ -718,6 +718,20 @@ static int parse_btf_arg(char *varname, return -EOPNOTSUPP; } + if (strcmp(varname, "$current") == 0) { + code->op = FETCH_OP_CURRENT; + /* If no typecast is specified for $current, use task_struct by default */ + if (!ctx->struct_btf) { + tid = bpf_find_btf_id("task_struct", BTF_KIND_STRUCT, &ctx->struct_btf); + if (tid < 0) { + trace_probe_log_err(ctx->offset, NO_BTF_ENTRY); + return -ENOENT; + } + ctx->last_struct = btf_type_skip_modifiers(ctx->struct_btf, tid, &tid); + } + goto found; + } + if (ctx->flags & TPARG_FL_TEVENT) { ret = parse_trace_event(varname, code, ctx); if (ret < 0) { @@ -756,8 +770,8 @@ static int parse_btf_arg(char *varname, return -ENOENT; } } - params = ctx->params; + params = ctx->params; for (i = 0; i < ctx->nr_params; i++) { const char *name = btf_name_by_offset(ctx->btf, params[i].name_off); @@ -1246,6 +1260,19 @@ static int parse_probe_vars(char *orig_arg, const struct fetch_type *t, return 0; } + /* $current returns the address of the current task_struct. */ + if (str_has_prefix(arg, "current")) { + arg += strlen("current"); + if (*arg == '-' && IS_ENABLED(CONFIG_PROBE_EVENTS_BTF_ARGS)) + return parse_btf_arg(orig_arg, pcode, end, ctx); + + if (*arg != '\0') + goto inval; + + code->op = FETCH_OP_CURRENT; + return 0; + } + #ifdef CONFIG_HAVE_FUNCTION_ARG_ACCESS_API len = str_has_prefix(arg, "arg"); if (len) { diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h index 44f113faae61..62645e847bd1 100644 --- a/kernel/trace/trace_probe.h +++ b/kernel/trace/trace_probe.h @@ -96,6 +96,7 @@ enum fetch_op { FETCH_OP_FOFFS, /* File offset: .immediate */ FETCH_OP_DATA, /* Allocated data: .data */ FETCH_OP_EDATA, /* Entry data: .offset */ + FETCH_OP_CURRENT, /* Current task_struct address */ // Stage 2 (dereference) op FETCH_OP_DEREF, /* Dereference: .offset */ FETCH_OP_UDEREF, /* User-space Dereference: .offset */ diff --git a/kernel/trace/trace_probe_tmpl.h b/kernel/trace/trace_probe_tmpl.h index f39b37fcdb3b..f630930288d2 100644 --- a/kernel/trace/trace_probe_tmpl.h +++ b/kernel/trace/trace_probe_tmpl.h @@ -112,6 +112,9 @@ process_common_fetch_insn(struct fetch_insn *code, unsigned long *val) case FETCH_OP_DATA: *val = (unsigned long)code->data; break; + case FETCH_OP_CURRENT: + *val = (unsigned long)current; + break; default: return -EILSEQ; }