From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from 66-220-144-179.mail-mxout.facebook.com (66-220-144-179.mail-mxout.facebook.com [66.220.144.179]) (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 BBA4033F5A2 for ; Fri, 20 Mar 2026 19:09:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=66.220.144.179 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774033795; cv=none; b=fEi/OS3UGjHaqKHV7J7GURJG/vaV5TY2LNtXaqydLG09uqw07JfZvsTme5s3psbm5PD/GAjiEKQr0xZGNBObLXDfTzuG6v3ya68uLbTnRdTRGUPpovDPjRzAUzcaVKPLcinSOHmjHXdMaaeT6kkAZcHP54C13fqBXos1BbbQzwI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774033795; c=relaxed/simple; bh=X+BV84ZzKnti1yFZH07fbCzlvx0avw0P7aGd4Z33PJ0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ZOmsEH8EwT1HtsiNc82b3P0SYy9UOpKXKgQ9zCPA7h3K4R4o3hxenakHF8wkSxQWbgv1waqJHJ6qp3789IrG4yDrOtr9rl6Hg3FOcgx9lsACKDP+Uljdf8Qlq3joysN3LElAcc+FIVYiGILEPYg2479/+6VkHrczTW5jgoi2s3A= 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=66.220.144.179 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 124572A7EAD44; Fri, 20 Mar 2026 12:09:38 -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 v3 4/9] dwarf_laoder: Handle locations with DW_OP_fbreg Date: Fri, 20 Mar 2026 12:09:38 -0700 Message-ID: <20260320190938.1972050-1-yonghong.song@linux.dev> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260320190917.1970524-1-yonghong.song@linux.dev> References: <20260320190917.1970524-1-yonghong.song@linux.dev> Precedence: bulk X-Mailing-List: bpf@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 | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) diff --git a/dwarf_loader.c b/dwarf_loader.c index 7b3f551..c259417 100644 --- a/dwarf_loader.c +++ b/dwarf_loader.c @@ -1196,6 +1196,7 @@ struct func_info { }; =20 #define PARM_DEFAULT_FAIL -1 +#define PARM_UNEXPECTED -2 =20 /* For DW_AT_location 'attr': * - if first location is DW_OP_regXX with expected number, return the r= egister; @@ -1204,7 +1205,8 @@ 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 conf_load *conf, + struct func_info *info) { Dwarf_Addr base, start, end; Dwarf_Op *expr, *entry_ops; @@ -1240,6 +1242,16 @@ 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 (info->signature_changed && conf->true_signature) + ret =3D PARM_UNEXPECTED; + break; /* match DW_OP_entry_value(DW_OP_regXX) at any location */ case DW_OP_entry_value: case DW_OP_GNU_entry_value: @@ -1327,11 +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, conf, info); =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_UNEXPECTED || (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 2.52.0