From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from 69-171-232-181.mail-mxout.facebook.com (69-171-232-181.mail-mxout.facebook.com [69.171.232.181]) (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 24D7438E13D for ; Thu, 26 Mar 2026 01:32:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=69.171.232.181 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774488729; cv=none; b=pII5eKwN/K2nHdccZ04r9VnUTZg7+Cay2u5feQgbI6nuL07eKOyo4lK/Qa/0RWePCXTHPApaA47Di6yVJs4VcBWI4oNEod5yGS+GVrkUbK3mNy7iJ1++vr9xF0NqOdp9hlFXn6/q/KrmtMY0uJq0wWymwPBERRwfiihal/lVXOU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774488729; c=relaxed/simple; bh=9lwDGxrEtsv/wZDeTm2u+YBU/Ts8T4ILLIU+2p5ZWog=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=XE/ZuM+8hQTtX3tixRuhXWaFHARf4Hh5b5A9diGrFxnqiTVEzfQugCb+QhMq9PE+sYieI2r2nww1bMHbKsffd1HJC1KqXj8r7wPhSRPRGTka+l/GqaS5mph636ffYzi4FHKrB4rHAdmcaRXXIMoKfAo94XyCn+3gjXdMnT91wgU= 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=69.171.232.181 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 C08952E280F44; Wed, 25 Mar 2026 18:31:59 -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 v4 03/11] dwarf_loader: Handle signatures with dead arguments Date: Wed, 25 Mar 2026 18:31:59 -0700 Message-ID: <20260326013159.2904078-1-yonghong.song@linux.dev> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260326013144.2901265-1-yonghong.song@linux.dev> References: <20260326013144.2901265-1-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 For llvm dwarf, the dead argument may be in the middle of DW_TAG_subprogram. So we introduce skip_idx in order to match expected registers properly. For example: 0x00042897: DW_TAG_subprogram DW_AT_name ("create_dev") DW_AT_calling_convention (DW_CC_nocall) DW_AT_type (0x0002429a "int") ... 0x000428ab: DW_TAG_formal_parameter DW_AT_name ("name") DW_AT_type (0x000242ed "char *") ... 0x000428b5: DW_TAG_formal_parameter DW_AT_location (indexed (0x3f) loclist =3D 0x0= 00027f8: [0xffffffff87681370, 0xffffffff8768137a): DW_OP_re= g5 RDI [0xffffffff8768137a, 0xffffffff87681392): DW_OP_re= g3 RBX [0xffffffff87681392, 0xffffffff876813ae): DW_OP_en= try_value(DW_OP_reg5 RDI), DW_OP_stack_value) DW_AT_name ("dev") DW_AT_type (0x00026859 "dev_t") ... With skip_idx, we can identify that the second original argument 'dev' becomes the first one after optimization. The previous patch has the following: 0x0533fd03: DW_TAG_subprogram DW_AT_name ("acpi_irq_penalty_update") DW_AT_calling_convention (DW_CC_nocall) DW_AT_type (0x05334dc7 "int") ... 0x0533fd15: DW_TAG_formal_parameter DW_AT_name ("str") DW_AT_type (0x05335918 "char *") ... 0x0533fd1f: DW_TAG_formal_parameter DW_AT_location (indexed (0x3b) loclist =3D 0x0= 0eb9d83: [0xffff80008419f2e0, 0xffff80008419f324): DW_OP_re= g1 W1 [0xffff80008419f324, 0xffff80008419f47c): DW_OP_re= g19 W19 [0xffff80008419f47c, 0xffff80008419f494): DW_OP_en= try_value(DW_OP_reg1 W1), DW_OP_stack_value [0xffff80008419f494, 0xffff80008419f498): DW_OP_re= g19 W19) DW_AT_name ("used") DW_AT_type (0x05334dc7 "int") ... It is also handled properly with parameter 'str' will have W0 register. With this patch, I checked x86_64 that the number of invalid true signatu= res is reduced from 532 to 96. This suggests that majority of optimized functions are ca= used by dead arguments. Signed-off-by: Yonghong Song --- dwarf_loader.c | 93 +++++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 88 insertions(+), 5 deletions(-) diff --git a/dwarf_loader.c b/dwarf_loader.c index 412a73e..c1b7763 100644 --- a/dwarf_loader.c +++ b/dwarf_loader.c @@ -1195,10 +1195,62 @@ static ptrdiff_t __dwarf_getlocations(Dwarf_Attri= bute *attr, =20 struct func_info { bool signature_changed; + int skip_idx; int nr_params; int param_start_regs[MAX_PRESCAN_PARAMS]; }; =20 +static int __get_type_byte_size(Dwarf_Die *die, struct cu *cu) +{ + Dwarf_Attribute attr; + if (dwarf_attr(die, DW_AT_type, &attr) =3D=3D NULL) + return 0; + + Dwarf_Die type_die; + if (dwarf_formref_die(&attr, &type_die) =3D=3D NULL) + return 0; + + /* A type does not have byte_size. + * 0x000dac83: DW_TAG_formal_parameter + DW_AT_location (indexed (0x385) loclist =3D 0x00016175: + [0xffff800080098cb0, 0xffff800080098cb4): DW_OP_breg8 W8+0 + [0xffff800080098cb4, 0xffff800080098ff4): DW_OP_breg31 WSP+16, DW_= OP_deref + [0xffff800080099054, 0xffff80008009908c): DW_OP_breg31 WSP+16, DW_= OP_deref) + DW_AT_name ("ubuf") + DW_AT_decl_file ("/home/yhs/work/bpf-next/arch/arm64/kernel/pt= race.c") + DW_AT_decl_line (886) + DW_AT_type (0x000d467e "const void *") + + * 0x000d467e: DW_TAG_pointer_type + DW_AT_type (0x000c4320 "const void") + + * 0x000c4320: DW_TAG_const_type + */ + if (dwarf_tag(&type_die) =3D=3D DW_TAG_pointer_type) + return cu->addr_size; + + uint64_t bsize =3D attr_numeric(&type_die, DW_AT_byte_size); + if (bsize =3D=3D 0) + return __get_type_byte_size(&type_die, cu); + + return bsize; +} + +static int get_type_byte_size(Dwarf_Die *die, struct cu *cu) +{ + int byte_size =3D 0; + + Dwarf_Attribute attr; + if (dwarf_attr(die, DW_AT_abstract_origin, &attr)) { + Dwarf_Die origin; + if (dwarf_formref_die(&attr, &origin)) + byte_size =3D __get_type_byte_size(&origin, cu); + } else { + byte_size =3D __get_type_byte_size(die, cu); + } + return byte_size; +} + /* Get the first DW_OP_X (should be a register) from a parameter's DW_AT= _location. */ static int parameter__peek_first_reg(Dwarf_Die *die) { @@ -1292,8 +1344,9 @@ static struct parameter *parameter__new(Dwarf_Die *= die, struct cu *cu, struct parameter *parm =3D tag__alloc(cu, sizeof(*parm)); =20 if (parm !=3D NULL) { - bool has_const_value; + bool has_const_value, true_sig_enabled; Dwarf_Attribute attr; + int reg_idx; =20 tag__init(&parm->tag, cu, die); parm->name =3D attr_string(die, DW_AT_name, conf); @@ -1303,8 +1356,10 @@ static struct parameter *parameter__new(Dwarf_Die = *die, struct cu *cu, if (!info->signature_changed) { if (cu->producer_clang || param_idx >=3D cu->nr_register_params) return parm; - } else if (param_idx >=3D cu->nr_register_params) { - return parm; + } else { + reg_idx =3D param_idx - info->skip_idx; + if (reg_idx >=3D cu->nr_register_params) + return parm; } =20 /* Parameters which use DW_AT_abstract_origin to point at @@ -1342,9 +1397,10 @@ static struct parameter *parameter__new(Dwarf_Die = *die, struct cu *cu, */ has_const_value =3D dwarf_attr(die, DW_AT_const_value, &attr) !=3D NUL= L; parm->has_loc =3D dwarf_attr(die, DW_AT_location, &attr) !=3D NULL; + true_sig_enabled =3D conf->true_signature && info->signature_changed; =20 if (parm->has_loc) { - int expected_reg =3D cu->register_params[param_idx]; + int expected_reg =3D cu->register_params[reg_idx]; int actual_reg =3D parameter__reg(&attr, expected_reg); =20 if (actual_reg < 0) @@ -1357,8 +1413,35 @@ static struct parameter *parameter__new(Dwarf_Die = *die, struct cu *cu, * contents. */ parm->unexpected_reg =3D 1; - } else if (has_const_value) { + } else if (has_const_value && !cu->producer_clang) { + parm->optimized =3D 1; + } else if (true_sig_enabled) { + int byte_size, num_regs, next_reg_idx; + + if (param_idx + 1 < info->nr_params) { + int next_start =3D info->param_start_regs[param_idx + 1]; + if (next_start >=3D 0) { + /* check whether we should preserve the argument or not */ + byte_size =3D get_type_byte_size(die, cu); + /* byte_size 0 should not happen. */ + if (!byte_size) { + parm->unexpected_reg =3D 1; + return parm; + } + + num_regs =3D (byte_size + cu->addr_size - 1) / cu->addr_size; + next_reg_idx =3D reg_idx + num_regs; + if (next_reg_idx < cu->nr_register_params && + next_start =3D=3D cu->register_params[next_reg_idx]) { + if (byte_size > cu->addr_size) + info->skip_idx--; + return parm; + } + } + } + parm->optimized =3D 1; + info->skip_idx++; } } =20 --=20 2.52.0