From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from pegase2.c-s.fr (pegase2.c-s.fr [93.17.235.10]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 7570024F587 for ; Mon, 24 Feb 2025 10:50:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=93.17.235.10 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740394206; cv=none; b=fpW8HTlYrlGMM/vpi4JLY3N6Jw86PlBmJSuPckQrPJXDHikUCyA8tXS7/Yc0wHUsLSNvwFTS8OEGCIydcEPvH+Gml0VDaZ9CJ+nlkjQM1epaiJbKjYJQ7iO+0EtD6Kw1WWBSpnAAVn34qYse5EGafYPAXAOscCJZB+HunlYsgEo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740394206; c=relaxed/simple; bh=n9CDmCoaBhrZIqqvdg49Kr+M5ALAwQnMC1HueNoG51c=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=TvYKE/yuP9QNmvLe3BN4CgKztihOxDw51zxi5AMO9BUwHp1Wt6L5c/GsF+DcXMxuL+KohLfBHpqNTLLvn/kJMFTyDAuQ6zdVHOARCq6aiDvvWSV/UQK2n3SlMcDDNxFbHxberEp5Tg8kpUj458eu21yLdGnQVa0bifrEoMshdA8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=csgroup.eu; spf=pass smtp.mailfrom=csgroup.eu; arc=none smtp.client-ip=93.17.235.10 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=csgroup.eu Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=csgroup.eu Received: from localhost (mailhub3.si.c-s.fr [172.26.127.67]) by localhost (Postfix) with ESMTP id 4Z1cXj4ksDz9sVM; Mon, 24 Feb 2025 11:33:57 +0100 (CET) X-Virus-Scanned: amavisd-new at c-s.fr Received: from pegase2.c-s.fr ([172.26.127.65]) by localhost (pegase2.c-s.fr [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id U8B0JvwyrIMy; Mon, 24 Feb 2025 11:33:57 +0100 (CET) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase2.c-s.fr (Postfix) with ESMTP id 4Z1cXj3fb9z9sVJ; Mon, 24 Feb 2025 11:33:57 +0100 (CET) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 67E258B765; Mon, 24 Feb 2025 11:33:57 +0100 (CET) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id B-CbSgzObSQb; Mon, 24 Feb 2025 11:33:57 +0100 (CET) Received: from [10.25.207.138] (unknown [10.25.207.138]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 35E968B763; Mon, 24 Feb 2025 11:33:57 +0100 (CET) Message-ID: Date: Mon, 24 Feb 2025 11:33:57 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] objtool: Skip unannotated intra-function call warning for bl+mflr pattern From: Christophe Leroy To: Sathvika Vasireddy , jpoimboe@kernel.org, peterz@infradead.org, npiggin@gmail.com, maddy@linux.ibm.com, Nathan Chancellor Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, llvm@lists.linux.dev References: <20250219162014.10334-1-sv@linux.ibm.com> <3223ec0e-c445-4bbf-ae72-276688e40908@csgroup.eu> Content-Language: fr-FR In-Reply-To: <3223ec0e-c445-4bbf-ae72-276688e40908@csgroup.eu> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Le 24/02/2025 à 08:15, Christophe Leroy a écrit : > > > Le 19/02/2025 à 17:20, Sathvika Vasireddy a écrit : >> Architectures like PowerPC use a pattern where the compiler generates a >> branch-and-link (bl) instruction that targets the very next instruction, >> followed by loading the link register (mflr) later. This pattern appears >> in the code like: >> >>   bl .+4 >>   li r5,0 >>   mflr r30 > > What compiler do you use ? Is it a very old version of GCC ? Oh, I see that this is a report on a projet version of clang ? compiler: clang version 21.0.0git Then I guess the bug needs to be fixed in Clang, not in the kernel. > > That sequence is not correct and should never be used by modern > compilers. It should be bcl 20,31,+4 instead. > > All such hand writen sequences have been removed from kernel assembly, > see commit c974809a26a1 ("powerpc/vdso: Avoid link stack corruption in > __get_datapage()") for details > > >> >> Objtool currently warns about this as an "unannotated intra-function >> call" because find_call_destination() fails to find any symbol at the >> target offset. Add a check to skip the warning when a branch targets >> the immediate next instruction in the same function. > > I think this should be done in arch_decode_instruction(), just set insn- > >type to INSN_OTHER when you see bl .+4 > > Something like: > > diff --git a/tools/objtool/arch/powerpc/decode.c b/tools/objtool/arch/ > powerpc/decode.c > index 53b55690f320..ca264c97ee8d 100644 > --- a/tools/objtool/arch/powerpc/decode.c > +++ b/tools/objtool/arch/powerpc/decode.c > @@ -55,7 +55,9 @@ int arch_decode_instruction(struct objtool_file *file, > const struct section *sec > >      switch (opcode) { >      case 18: /* b[l][a] */ > -        if ((ins & 3) == 1) /* bl */ > +        if (ins == 0x48000005)    /* bl .+4 */ > +            typ = INSN_OTHER; > +        else if ((ins & 3) == 1) /* bl */ >              typ = INSN_CALL; > >          imm = ins & 0x3fffffc; > > > >> >> Reported-by: kernel test robot >> Closes: https://lore.kernel.org/oe-kbuild-all/202502180818.XnFdv8I8- >> lkp@intel.com/ >> Signed-off-by: Sathvika Vasireddy >> --- >>   tools/objtool/check.c | 6 ++++++ >>   1 file changed, 6 insertions(+) >> >> diff --git a/tools/objtool/check.c b/tools/objtool/check.c >> index 753dbc4f8198..3f7cf2c917b5 100644 >> --- a/tools/objtool/check.c >> +++ b/tools/objtool/check.c >> @@ -1613,6 +1613,7 @@ static struct symbol >> *find_call_destination(struct section *sec, unsigned long o >>    */ >>   static int add_call_destinations(struct objtool_file *file) >>   { >> +       struct instruction *next_insn; >>          struct instruction *insn; >>          unsigned long dest_off; >>          struct symbol *dest; >> @@ -1625,6 +1626,11 @@ static int add_call_destinations(struct >> objtool_file *file) >>                  reloc = insn_reloc(file, insn); >>                  if (!reloc) { >>                          dest_off = arch_jump_destination(insn); >> + >> +                       next_insn = next_insn_same_func(file, insn); >> +                       if (next_insn && dest_off == next_insn->offset) >> +                               continue; >> + >>                          dest = find_call_destination(insn->sec, >> dest_off); >> >>                          add_call_dest(file, insn, dest, false); >> -- >> 2.39.3 >> >