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 B10AE284B3B; Wed, 17 Jun 2026 01:03:35 +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=1781658216; cv=none; b=UgdiDeULL8RBvwfo75dlUjHNtN/sxxVSGE3pv50V74vdg0xuGNuPIwZnhkgCWPkQ6PScM5LhotZIJXhsD5datGI5nPMFBYI3IrOY5Jca3pYk6VyOdnoJFzX7gY2DIBQkBqgrFsDz4CaLx7OhDlpaEbLHxM+Bnd1tSqx8Zq2JROU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781658216; c=relaxed/simple; bh=w64uNwld4O6Cp1Irr3DPkmPvikTuVyodZTvSbSTScHY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=LuaNLwjQCD46tK3Wby0DC1fb4NwGFM3oa8u56kNg6VJ5DXuoLvIEYL+RDoWAJj2uOrQXIRrAljhgZLOMCpTzEINjLF0+y51gqkODsOce0TR1hKkx0qE1p70yPlyb6BnDf1CmG0q4AHmiLvr9KPNU1PRijal9WZd3bEVt9oqt8E4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=nXG8A/n4; 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="nXG8A/n4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5F05A1F00A3A; Wed, 17 Jun 2026 01:03:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781658215; bh=GZLBl8vR0/182jG6QpW6fSRs4D73rqfVy+fQ+kt0u9E=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=nXG8A/n4cjNec8pJAA65wdS2QIthSGbTrKuHYE0SlWPKd17fG77UqB1Towr9zv1bt n+9rn9rnxqVAjzvEGnSTP/sXv7zMEvXuE/nO3htLF1s2M02ciyyGR2VQAZKgRydFmO aGPW4qB3bJjzSJSk3Tb8eL2LpFc8Wjp3oklBvYqrlmO8zP+ngimqKJcGvjxiwnTHRG gvTWMJAMigvWEKtA9DNM8R2ZEt4nasu6nj3I/lZe2ijBlshskseGmo+cXf5qxCqSFj QOZtly9EzRVAxebyQuvcHh50iW3MhJezuKXgmap6K4GXzWcJwSR0mX9ueyxAsorQ26 CbmQ4//LwjLrw== 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: [PATCH v5 5/7] tracing/probes: Add $current variable support Date: Wed, 17 Jun 2026 10:03:31 +0900 Message-ID: <178165821121.269421.7894063612460991879.stgit@devnote2> X-Mailer: git-send-email 2.43.0 In-Reply-To: <178165816303.269421.7302603996990753309.stgit@devnote2> References: <178165816303.269421.7302603996990753309.stgit@devnote2> User-Agent: StGit/0.19 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit From: Masami Hiramatsu (Google) Since we can use the BTF to cast value to a structure pointer type, it is useful to introduce "$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 v5: - Use s32 for bof_find_btf_id(). Changes in v4: - Add $current in README when CONFIG_HAVE_FUNCTION_ARG_ACCESS_API=y case. - Fix to prohibit using $current in eprobes and address based kprobes. Changes in v3: - Remove $current support from eprobes (because eprobes is only for event) - Prohibit uprobes to use $current. 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/fprobetrace.rst | 1 + Documentation/trace/kprobetrace.rst | 1 + kernel/trace/trace.c | 4 ++-- kernel/trace/trace_probe.c | 38 ++++++++++++++++++++++++++++++++++- kernel/trace/trace_probe.h | 1 + kernel/trace/trace_probe_tmpl.h | 3 +++ 6 files changed, 45 insertions(+), 3 deletions(-) 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. + $current : Fetch the address of the current task_struct. +|-[u]OFFS(FETCHARG) : Fetch memory at FETCHARG +|- OFFS address.(\*3)(\*4) \IMM : Store an immediate value to the argument. NAME=FETCHARG : Set NAME as the argument name of FETCHARG. diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 0e36af853199..7a5676524f1a 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -4323,13 +4323,13 @@ static const char readme_msg[] = "\t args: =fetcharg[:type]\n" "\t fetcharg: (%|$), @
, @[+|-],\n" #ifdef CONFIG_HAVE_FUNCTION_ARG_ACCESS_API - "\t $stack, $stack, $retval, $comm, $arg,\n" + "\t $stack, $stack, $retval, $comm, $arg, $current\n" #ifdef CONFIG_PROBE_EVENTS_BTF_ARGS "\t [(structname[,field])][->field[->field|.field...]],\n" "\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, $comm\n" diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c index 0f2be8c817fc..93edac7fc943 100644 --- a/kernel/trace/trace_probe.c +++ b/kernel/trace/trace_probe.c @@ -730,6 +730,24 @@ static int parse_btf_arg(char *varname, goto found; } + if (strcmp(varname, "$current") == 0) { + code->op = FETCH_OP_CURRENT; + /* If no typecast is specified for $current, use task_struct by default */ + if (!ctx->struct_btf) { + s32 ttid = bpf_find_btf_id("task_struct", BTF_KIND_STRUCT, + &ctx->struct_btf); + + if (ttid < 0) { + trace_probe_log_err(ctx->offset, NO_BTF_ENTRY); + return -ENOENT; + } + /* btf_type_skip_modifier() requires u32 for type id. */ + tid = ttid; + ctx->last_struct = btf_type_skip_modifiers(ctx->struct_btf, tid, &tid); + } + goto found; + } + if (ctx->flags & TPARG_FL_RETURN && !strcmp(varname, "$retval")) { code->op = FETCH_OP_RETVAL; /* Check whether the function return type is not void, even with typecast. */ @@ -763,8 +781,8 @@ 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); @@ -1254,6 +1272,24 @@ 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")) { + /* $current is only supported by kernel probe and need function name. */ + if (!(ctx->flags & TPARG_FL_KERNEL) || !ctx->funcname) { + err = TP_ERR_BAD_VAR; + goto inval; + } + 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; }