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 011DF22FF22; Mon, 15 Jun 2026 01:14:48 +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=1781486090; cv=none; b=oIz0Za+vUvod6SFDUiz/5LGpu/N4QuCyrVDSjYdDx0IZkTRzet5u0sHgGb6vPKYSZvkSsrrkH8JDoHz5Y/C8P9sJ/g/VYcYK/7YUlO3+yD2LMcJ0jJw6S5Id4jXC7Gudjoj5oWu2z9lfYuszOjAwyeLXK/ssVsWcmKAxjN9lVkk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781486090; c=relaxed/simple; bh=fdvqdaYvOtH+8uNMrL0IxQPTL8XKFWm2G3HCIriAKeg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=CE3Ap+CgBmC+V5cgGCKR0w/SribQKH9mloG1Us+x59nbibJZtVAxgZD7B+RbRgxLLOUPsjjnwhLcaWm346GteBlZzKJfsoKgqBgtomWUniRlrQGAIykWLW9mXbvzIf5i7/BPhsqrgbR5vIXiq25+4D/PgbeDFRwsDbp8m5TtOKk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ae432iyr; 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="ae432iyr" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7BA421F000E9; Mon, 15 Jun 2026 01:14:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781486088; bh=WSkxJw89RhbeWR1oprV6A8xiDYsJDAmP5OjsH2F8pX0=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=ae432iyrnVRbyEfXiaWI3cg0+/p/RsgSqx4MS/a09rKjAOiIF+l+e+mIijzSKGQ7j WQhsc+J1jMFYHOfsAH4hFQdmXGXsVF0rB88/d1yGG/tThRdL8qAMeVvHRQlRM0tAmq BiWz4mYUvg+0/wDNfdgFiqi80foiIdPHPPJd6kF1K/Wp/8hir2bU6Nn3mUlsgfHZc/ ty5vr7tzqmF+tdTnBNO7DBg3JErVwW88JXEXhcGQkiHCJSVauyMNWY0vxgibIsGMG/ ZIdJmizLWMMVYMoRblMkIJzOKOta32J9zsMrjQI4jJwPEqlCDGt3o0tgET0tYzT0PB 2G0m2ecBt87EA== 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 v4 5/7] tracing/probes: Add $current variable support Date: Mon, 15 Jun 2026 10:14:44 +0900 Message-ID: <178148608419.185520.10391291375504332719.stgit@devnote2> X-Mailer: git-send-email 2.43.0 In-Reply-To: <178148603548.185520.3389196102475741865.stgit@devnote2> References: <178148603548.185520.3389196102475741865.stgit@devnote2> User-Agent: StGit/0.19 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit From: Masami Hiramatsu (Google) Since we can use the BTF to cast value to a structure pointer type, it is useful to introduce "$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 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 | 34 +++++++++++++++++++++++++++++++++- kernel/trace/trace_probe.h | 1 + kernel/trace/trace_probe_tmpl.h | 3 +++ 6 files changed, 41 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, $comm\n" diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c index 3ead93de2d93..f5155340a325 100644 --- a/kernel/trace/trace_probe.c +++ b/kernel/trace/trace_probe.c @@ -730,6 +730,20 @@ static int parse_btf_arg(char *varname, goto found; } + if (strcmp(varname, "$current") == 0) { + code->op = FETCH_OP_CURRENT; + /* If no typecast is specified for $current, use task_struct by default */ + if (!ctx->struct_btf) { + tid = bpf_find_btf_id("task_struct", BTF_KIND_STRUCT, &ctx->struct_btf); + if (tid < 0) { + trace_probe_log_err(ctx->offset, NO_BTF_ENTRY); + return -ENOENT; + } + ctx->last_struct = btf_type_skip_modifiers(ctx->struct_btf, tid, &tid); + } + goto found; + } + if (ctx->flags & TPARG_FL_RETURN && !strcmp(varname, "$retval")) { code->op = FETCH_OP_RETVAL; /* Check whether the function return type is not void */ @@ -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); @@ -1247,6 +1261,24 @@ 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; }