From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from 66-220-155-178.mail-mxout.facebook.com (66-220-155-178.mail-mxout.facebook.com [66.220.155.178]) (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 29E923D7D70 for ; Mon, 9 Mar 2026 15:32:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=66.220.155.178 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773070368; cv=none; b=r83KY8m9PIeUx6Y0atYS5q+zwjajdJ2wn6X08Khq2R63/GhjY2h97JQvyIuHhU+ZKbfyQA9+i9d9iW7ynQyZ20NQJ7ojZWPywdx1kOcLksf0tEtF4BiX8Z1N0D7D0byAJxBeNrXASna1wP8pxtpbK63ZnTi8Pqg+AeABL20M5Kw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773070368; c=relaxed/simple; bh=gnYZLY+Woj8rWs+RO4xWLRxCNIHeQIKBF0zm5htDTWo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=u2ZbepN/B+FOpAICc7/RbK+sSnSmdG6Ej1GETtW+g3sr9NQNoQN1o79raCCgKDXAgPe66dao1wVjqe+FpACDWkOoVWBtMe9Ukzu7RJtcLBFQnAAfPCOsqX6Ep/kGXH5Fqmxb3zwV1cNCAjvhCveOBxB3U0AlcaJvD+qv4YTK+y4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.dev; spf=fail smtp.mailfrom=linux.dev; arc=none smtp.client-ip=66.220.155.178 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=linux.dev Received: by devvm16039.vll0.facebook.com (Postfix, from userid 128203) id 278682494435E; Mon, 9 Mar 2026 08:32:36 -0700 (PDT) From: Yonghong Song To: Alan Maguire , Arnaldo Carvalho de Melo , dwarves@vger.kernel.org Cc: Alexei Starovoitov , Andrii Nakryiko , bpf@vger.kernel.org, kernel-team@fb.com Subject: [PATCH dwarves v2 4/9] dwarf_laoder: Handle locations with DW_OP_fbreg Date: Mon, 9 Mar 2026 08:32:36 -0700 Message-ID: <20260309153236.1918945-1-yonghong.song@linux.dev> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260309153215.1917033-1-yonghong.song@linux.dev> References: <20260309153215.1917033-1-yonghong.song@linux.dev> Precedence: bulk X-Mailing-List: dwarves@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable DW_OP_fbreg means the parameter value will be stored on the stack. So the corresponding parameter register is not used. For example: 0x071f7717: DW_TAG_subprogram DW_AT_name ("jent_health_failure") DW_AT_calling_convention (DW_CC_nocall) DW_AT_type (0x071f7626 "unsigned int") ... 0x071f7728: DW_TAG_formal_parameter DW_AT_location (DW_OP_fbreg -8) DW_AT_name ("ec") DW_AT_type (0x071f7ab6 "rand_data *") ... 0x071f7734: NULL In the above, the parameter 'ec' type is a pointer so it perfectly fits into a register. But the location uses 'DW_OP_fbreg -8' which prevents from generating a function with true signatures. Signed-off-by: Yonghong Song --- dwarf_loader.c | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-) diff --git a/dwarf_loader.c b/dwarf_loader.c index 7da3926..d538607 100644 --- a/dwarf_loader.c +++ b/dwarf_loader.c @@ -1196,6 +1196,7 @@ struct func_info { }; =20 #define PARM_DEFAULT_FAIL -1 +#define PARM_FAIL_CLANG -2 =20 /* For DW_AT_location 'attr': * - if first location is DW_OP_regXX with expected number, return the r= egister; @@ -1204,7 +1205,7 @@ struct func_info { * list, return the register; otherwise save register for later return * - otherwise if no register was found for locations, return PARM_DEFAU= LT_FAIL. */ -static int parameter__reg(Dwarf_Attribute *attr, int expected_reg) +static int parameter__reg(Dwarf_Attribute *attr, int expected_reg, struc= t cu *cu, struct conf_load *conf) { Dwarf_Addr base, start, end; Dwarf_Op *expr, *entry_ops; @@ -1240,6 +1241,16 @@ static int parameter__reg(Dwarf_Attribute *attr, i= nt expected_reg) if (ret =3D=3D expected_reg) goto out; break; + case DW_OP_fbreg: + /* The locaiton like + * DW_AT_location (DW_OP_fbreg +) + * indicates that the parameter is on the stack. But it is possible + * that the parameter can fit in register(s). So conservatively + * mark this parameter not suitable for true signatures. + */ + if (cu->producer_clang && conf->true_signature) + ret =3D PARM_FAIL_CLANG; + break; /* match DW_OP_entry_value(DW_OP_regXX) at any location */ case DW_OP_entry_value: case DW_OP_GNU_entry_value: @@ -1328,11 +1339,11 @@ static struct parameter *parameter__new(Dwarf_Die= *die, struct cu *cu, =20 if (parm->has_loc) { int expected_reg =3D cu->register_params[reg_idx]; - int actual_reg =3D parameter__reg(&attr, expected_reg); + int actual_reg =3D parameter__reg(&attr, expected_reg, cu, conf); =20 if (actual_reg =3D=3D PARM_DEFAULT_FAIL) parm->optimized =3D 1; - else if (expected_reg >=3D 0 && expected_reg !=3D actual_reg) + else if (actual_reg =3D=3D PARM_FAIL_CLANG || (expected_reg >=3D 0 &&= expected_reg !=3D actual_reg)) /* mark parameters that use an unexpected * register to hold a parameter; these will * be problematic for users of BTF as they --=20 2.47.3