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Tue, 29 Nov 2022 15:13:27 +0000 (GMT) Received: from [9.109.198.140] (unknown [9.109.198.140]) by d06av25.portsmouth.uk.ibm.com (Postfix) with ESMTP; Tue, 29 Nov 2022 15:13:26 +0000 (GMT) Message-ID: <6cdad32e-782d-5bb5-f7e9-a44fb0b6444d@linux.ibm.com> Date: Tue, 29 Nov 2022 20:43:25 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.12.0 Subject: Re: linux-next: build warnings after merge of the powerpc-objtool tree Content-Language: en-US To: Stephen Rothwell , Michael Ellerman , PowerPC References: <20221125143012.6426c2b9@canb.auug.org.au> From: Sathvika Vasireddy In-Reply-To: <20221125143012.6426c2b9@canb.auug.org.au> Content-Type: text/plain; charset=UTF-8; format=flowed X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: F2lH_XEpazIbiNeK9BvuK-gXke5aRu4x X-Proofpoint-GUID: F2lH_XEpazIbiNeK9BvuK-gXke5aRu4x Content-Transfer-Encoding: 8bit X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.219,Aquarius:18.0.895,Hydra:6.0.545,FMLib:17.11.122.1 definitions=2022-11-29_09,2022-11-29_01,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxscore=0 priorityscore=1501 mlxlogscore=999 malwarescore=0 phishscore=0 impostorscore=0 lowpriorityscore=0 spamscore=0 suspectscore=0 clxscore=1011 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2210170000 definitions=main-2211290083 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Naveen N. Rao" , Linux Next Mailing List , Sathvika Vasireddy , Linux Kernel Mailing List Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Hi all, On 25/11/22 09:00, Stephen Rothwell wrote: > Hi all, > > After merging the powerpc-objtool tree, today's linux-next build (powerpc > pseries_le_defconfig) produced these warnings: > > arch/powerpc/kernel/head_64.o: warning: objtool: end_first_256B(): can't find starting instruction > arch/powerpc/kernel/optprobes_head.o: warning: objtool: optprobe_template_end(): can't find starting instruction > > I have no idea what started this (they may have been there yesterday). I was able to recreate the above mentioned warnings with pseries_le_defconfig and powernv_defconfig. The regression report also mentions a warning (https://lore.kernel.org/oe-kbuild-all/202211282102.QUr7HHrW-lkp@intel.com/) seen with arch/powerpc/kernel/kvm_emul.S assembly file.  [1] arch/powerpc/kernel/optprobes_head.o: warning: objtool: optprobe_template_end(): can't find starting instruction  [2] arch/powerpc/kernel/kvm_emul.o: warning: objtool: kvm_template_end(): can't find starting instruction  [3] arch/powerpc/kernel/head_64.o: warning: objtool: end_first_256B(): can't find starting instruction The warnings [1] and [2] go away after adding 'nop' instruction. Below diff fixes it for me: diff --git a/arch/powerpc/kernel/optprobes_head.S b/arch/powerpc/kernel/optprobes_head.S index cd4e7bc32609..ea4e3bd82f4f 100644 --- a/arch/powerpc/kernel/optprobes_head.S +++ b/arch/powerpc/kernel/optprobes_head.S @@ -134,3 +134,4 @@ optprobe_template_ret:         .global optprobe_template_end  optprobe_template_end: +       nop diff --git a/arch/powerpc/kernel/kvm_emul.S b/arch/powerpc/kernel/kvm_emul.S index 7af6f8b50c5d..41fd664e3ba0 100644 --- a/arch/powerpc/kernel/kvm_emul.S +++ b/arch/powerpc/kernel/kvm_emul.S @@ -352,3 +352,4 @@ kvm_tmp_end:  .global kvm_template_end  kvm_template_end: +       nop For warning [3], objtool is throwing can't find starting instruction warning because it finds that the symbol (end_first_256B) is zero sized, and such symbols are not added to the rbtree. I tried to fix it by adding a 'nop' instruction (pasted diff below), but that resulted in a kernel build failure. diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S index 874efd25cc45..d48850fe159f 100644 --- a/arch/powerpc/kernel/head_64.S +++ b/arch/powerpc/kernel/head_64.S @@ -192,6 +192,7 @@ __secondary_hold:         EMIT_BUG_ENTRY 0b, __FILE__, __LINE__, 0  #endif  CLOSE_FIXED_SECTION(first_256B) +nop  /*   * On server, we include the exception vectors code here as it diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S index 26f8fef53c72..f7517d443e9b 100644 --- a/arch/powerpc/kernel/exceptions-64s.S +++ b/arch/powerpc/kernel/exceptions-64s.S @@ -3104,9 +3104,13 @@ __end_interrupts:  DEFINE_FIXED_SYMBOL(__end_interrupts, virt_trampolines)  CLOSE_FIXED_SECTION(real_vectors); +nop  CLOSE_FIXED_SECTION(real_trampolines); +nop  CLOSE_FIXED_SECTION(virt_vectors); +nop  CLOSE_FIXED_SECTION(virt_trampolines); +nop  USE_TEXT_SECTION() I'm not very sure on how to address this particular warning (arch/powerpc/kernel/head_64.o: warning: objtool: end_first_256B(): can't find starting instruction). Given that there are no calls to _mcount, one workaround is to skip objtool from running on arch/powerpc/kernel/head_64.o file. The below diff works for me: diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile index 9b6146056e48..9ef6a040d875 100644 --- a/arch/powerpc/kernel/Makefile +++ b/arch/powerpc/kernel/Makefile @@ -219,3 +219,5 @@ $(obj)/vdso64_wrapper.o : $(obj)/vdso/vdso64.so.dbg  # for cleaning  subdir- += vdso + +OBJECT_FILES_NON_STANDARD_head_64.o := y Thanks, Sathvika