From nobody Fri Dec 19 13:21:55 2025 Received: from mail-pj1-f46.google.com (mail-pj1-f46.google.com [209.85.216.46]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A70A5220F3A for ; Sun, 7 Dec 2025 14:27:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.46 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765117677; cv=none; b=MI6YR9Tt4vLWUlf6dgxiCimpSoV3q0cmKqvXwoslwxdzy3UtkmNKI4q4nlFUhLFmrnK/ORFjXbacWvnnBqu00JGqRvVwWA5+PfiqnkkZbt0iJlqiTkQJqQGvlNl+slGE/0PUod4+NQXrqlwDUwxkquMfnZCITXwZHgJWyhJOXpE= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765117677; c=relaxed/simple; bh=30o7EXsT+3UE9XemGnLUmRBLG1W6L02/uoH/F43nEZc=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=ni0OYliHc/Ak1QMIRvUa5DPe2kvit3zonBPCh43YHBL7bCfTOzclJ3Rn3ZQsbdul1DJZxnbqqlzYXKZAKAyBA+8GIJWCfJlIUJIaZ9otTZJjgbsvhGp+Ezk1MZMJiJ/hNiEyWIeko0Xt7m7y/GOpFxw4RlaYMpuY1H/oy23tem4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=f/f+c+Xu; arc=none smtp.client-ip=209.85.216.46 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="f/f+c+Xu" Received: by mail-pj1-f46.google.com with SMTP id 98e67ed59e1d1-349ff18445aso99987a91.3 for ; Sun, 07 Dec 2025 06:27:52 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1765117671; x=1765722471; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=lZnyUry+1w8xao5+MHyxhYILKDa1nn4nE9blPajp6gw=; b=f/f+c+XuZqgkMEXPAy1kmWFMbvXsQ4xErsuAjK5f43O/Eh6s72iB3qhtqE+p2i1lgK TY5Bd681ke2tB2GYFFQmKTHlxjumkGsS5qxj5irM98b128seCDdKKy4fvbIx4au6NGtU YozjzPykK209V1yW5H7WQKT6UJVZjGF1T08RuoGnavrTU1zGptT6GKGcWgt5ciOv6ehK +OjKssIuE9HUH6YgVIPfUyE4T/uUKgxXd44pO65EwvsgHZz4yPnuQy+GNF8ikctztMGE nxd5BvHwka0JzUijOQQUIEq050A4d9ZBoM7lN6aZoBzh7FDvcGigIJAFEoHIiXLKVzEC IB8w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1765117671; x=1765722471; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=lZnyUry+1w8xao5+MHyxhYILKDa1nn4nE9blPajp6gw=; b=RPp0OKfmBhR6M1nCnfBofBV5xsN18npMsDbvzWlON73AIh0ouZYM2yISm9oUlp51bU kMrXzwSmsxzVH79BlyjGVkzp+vpxK9yzzw/5UFSSAJL58ZP3dHfittLf/neZ/eQyVf+c ML7HqS5d0bOtPOSjR+MYkaUTLY+oq5mdrtgXZIblYooMlm0uRCtJ2tOkVaJ0pUIbz2ZE 7JQ0gihfg5u1TeQo0YPSufhkOtV9QKVB92vVqNKDW8C0IviF2h3KLHqFgBsNh1QXWQuL /1MxFpVCJcYCeznjA1cefrok3lDVkGFIUalxvz9bKxE3sbWC2WdfRGTn1uD8ptKFLJev akmQ== X-Forwarded-Encrypted: i=1; AJvYcCUd3SlKGmZFYio8sp+y3ZZhDyYl1UGCfYTF3FUGbbkUY/WsDQ6wfztpt+WkiPyS9WJR1ERxz2Qz/f5cBY0=@vger.kernel.org X-Gm-Message-State: AOJu0Yy1ufEoYhKVrO+i8hsBQ11Glzar+V3qQoY74/vgr/FN3BMCqQLZ MqkNKb4DHCznXzFsgw9CDMC+v7nKssnNexE2HS32/ZBgBijVwCYfgzlH X-Gm-Gg: ASbGnctl5ZpdFrEYlIkSkrmT9R04FJD8Ag22/a/yHCNZCvNCAKBKinIYOXTbTpMjB1L PDCFpE5fcvK1jyhQm+4GYEqEkd4esQm7X2eNHve3PmaZmenp+jHOdEjcf7W2UDn6iOj/jmOYy5K 7nOz2rk207TusdG5buk0UFacU1z89l3U0+uUSlN52LN4o530QQaZGbSgLMAME75w7XZ3maeBBFc b6rQE94esPGEppuadiN3ARnE6VdGgHkAOpQlkHsEpkjU54Wic0NS0OtIlRci1bTq1SrukRHTq7R pWVzPjfxEWq/A5UIb3WhdFaGvlmWCS+XlqcNyFLG94q7qyxzVmaX+1mKDXpGI61AH56Cv+4i7lH 8Q+ndn013wP8GxM755WFvkdiRESQiS/e5ihWhUOjXpiGY2lTkGqFYVBEloENwUXKaChg04n6mk8 vCbQyXzjfE+YxLtT+alWmBe71adR8= X-Google-Smtp-Source: AGHT+IH9mYL+8pQfNgZ4r8ZFqW+QSWz3AKdRwbEmCblz9taenxcf6eaYppGqEuojMUEJzBiNafSuyw== X-Received: by 2002:a17:90b:5546:b0:343:eb40:8e01 with SMTP id 98e67ed59e1d1-349a26223e5mr3565025a91.27.1765117670867; Sun, 07 Dec 2025 06:27:50 -0800 (PST) Received: from pengdl-pc.mioffice.cn ([43.224.245.249]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-bf686c32deesm9514792a12.13.2025.12.07.06.27.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 07 Dec 2025 06:27:49 -0800 (PST) From: Donglin Peng To: rostedt@goodmis.org Cc: linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org, pengdonglin , Masami Hiramatsu , Xiaoqin Zhang Subject: [PATCH v1 1/2] fgraph: use BTF to trim and filter return values Date: Sun, 7 Dec 2025 22:27:41 +0800 Message-Id: <20251207142742.229924-2-dolinux.peng@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20251207142742.229924-1-dolinux.peng@gmail.com> References: <20251207142742.229924-1-dolinux.peng@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: pengdonglin The current funcgraph-retval implementation has two limitations: 1. It prints a return value even when the traced function returns void. 2. When the return type is narrower than a register, the printed value may be incorrect because high bits can contain undefined data. Both issues are addressed by using BTF to obtain the precise return type of each traced function: - Return values are now printed only for functions whose return type is not void. - The value is truncated to the actual width of the return type, ensuring correct representation. These changes make the funcgraph-retval output more accurate and remove noise from void functions. Cc: Steven Rostedt (Google) Cc: Masami Hiramatsu Cc: Xiaoqin Zhang Signed-off-by: pengdonglin --- kernel/trace/trace_functions_graph.c | 64 +++++++++++++++++++++++----- 1 file changed, 54 insertions(+), 10 deletions(-) diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_func= tions_graph.c index 17c75cf2348e..9e63665c81e2 100644 --- a/kernel/trace/trace_functions_graph.c +++ b/kernel/trace/trace_functions_graph.c @@ -15,6 +15,7 @@ =20 #include "trace.h" #include "trace_output.h" +#include "trace_btf.h" =20 /* When set, irq functions might be ignored */ static int ftrace_graph_skip_irqs; @@ -865,6 +866,46 @@ static void print_graph_retaddr(struct trace_seq *s, s= truct fgraph_retaddr_ent_e =20 #if defined(CONFIG_FUNCTION_GRAPH_RETVAL) || defined(CONFIG_FUNCTION_GRAPH= _RETADDR) =20 +static void trim_retval(unsigned long func, unsigned long *retval, bool *p= rint_retval) +{ + const struct btf_type *t; + char name[KSYM_NAME_LEN]; + struct btf *btf; + u32 v, msb; + + if (!IS_ENABLED(CONFIG_DEBUG_INFO_BTF)) + return; + + if (lookup_symbol_name(func, name)) + return; + + t =3D btf_find_func_proto(name, &btf); + if (IS_ERR_OR_NULL(t)) + return; + + t =3D btf_type_skip_modifiers(btf, t->type, NULL); + switch (t ? BTF_INFO_KIND(t->info) : BTF_KIND_UNKN) { + case BTF_KIND_UNKN: + *print_retval =3D false; + break; + case BTF_KIND_ENUM: + case BTF_KIND_ENUM64: + msb =3D BITS_PER_BYTE * t->size - 1; + *retval &=3D GENMASK(msb, 0); + break; + case BTF_KIND_INT: + v =3D *(u32 *)(t + 1); + if (BTF_INT_ENCODING(v) =3D=3D BTF_INT_BOOL) + msb =3D 0; + else + msb =3D BTF_INT_BITS(v) - 1; + *retval &=3D GENMASK(msb, 0); + break; + default: + break; + } +} + static void print_graph_retval(struct trace_seq *s, struct ftrace_graph_en= t_entry *entry, struct ftrace_graph_ret *graph_ret, void *func, u32 opt_flags, u32 trace_flags, int args_size) @@ -884,17 +925,20 @@ static void print_graph_retval(struct trace_seq *s, s= truct ftrace_graph_ent_entr print_retaddr =3D !!(opt_flags & TRACE_GRAPH_PRINT_RETADDR); #endif =20 - if (print_retval && retval && !hex_format) { - /* Check if the return value matches the negative format */ - if (IS_ENABLED(CONFIG_64BIT) && (retval & BIT(31)) && - (((u64)retval) >> 32) =3D=3D 0) { - err_code =3D sign_extend64(retval, 31); - } else { - err_code =3D retval; + if (print_retval) { + trim_retval((unsigned long)func, &retval, &print_retval); + if (print_retval && retval && !hex_format) { + /* Check if the return value matches the negative format */ + if (IS_ENABLED(CONFIG_64BIT) && (retval & BIT(31)) && + (((u64)retval) >> 32) =3D=3D 0) { + err_code =3D sign_extend64(retval, 31); + } else { + err_code =3D retval; + } + + if (!IS_ERR_VALUE(err_code)) + err_code =3D 0; } - - if (!IS_ERR_VALUE(err_code)) - err_code =3D 0; } =20 if (entry) { --=20 2.34.1