From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from sonic301-20.consmr.mail.gq1.yahoo.com (sonic301-20.consmr.mail.gq1.yahoo.com [98.137.64.146]) by sourceware.org (Postfix) with ESMTPS id BB27D3858430 for ; Sat, 16 Apr 2022 04:44:12 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org BB27D3858430 X-SONIC-DKIM-SIGN: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yahoo.com; s=s2048; t=1650084251; bh=F78dhIIOOeiB7tD2JcgLJWQHQhJF3EUmnPhhi0MRIFm=; h=X-Sonic-MF:Date:From:Subject:To:From:Subject; b=LuuExcsPjUFQ1JZUYtHT+DfFx7ZEKBwcpQyhO2R4ckkfglZFX9TRA36CzDzUeBOtdDwYaaG4KJP/Q4qdQ9FHvqO1fVheIozDlhVacLTMQoRhtCA+UGmHCrxUtAQ9AIAC9Y/E2+r48KnFK4BzzfeVv9DSDJ0J2sbzckPZJj0dtNvFxBxxendLTnPtqUYdi6Z0Ro9bRJPfkQFhf1gWbHAo3ZzvKEkdR6MDnfW0wRGPol1I0mN+f++UFLq2AF5Zvx4k1EdfwNoX+RTmtOp2o2LcDDBTyLhlL467dCmQGBx0bet71mx07nhKTMlRA/nSlZ024al2Qlvz0o24wYKRfSuyzQ== X-YMail-OSG: bk5GqcsVM1kjEDnohoph5uw8GAdCwtqdWbObSgU_wI5NJwQsRbk6TLRXzusO3J9 fX4rXCh_NI9c1UTJI5zZlKWlzP9c6KMfLITc587xUhTnEGH8ii5xDW.6HSResUSDM5AormS6TYbm IwUWf4SWw_uDd38.d0w96PkTrDYY3PqnPNnl0N8rh9vzRFHCMN6_YgrKJodZ5dNZ_fnf6URhU2aC lXFTmyaDfvwvpGbcd6TnfBdJody2IW.7ofC.jKVZfhQvYqabCb7dDrwQDeCC3hALrj37OTK4wrls 7ggplU94f27psbab54nMbnYuaVgoBcuW6auZhVJDIe4NMDl_Dp50gWVoBwx7Pytim25vbGwmY4d4 pY65MR3D5tJIBjnIqK6NnNHNARzxc53qyaEpztEst6I5.RybV1VQWQxgiYGYHYmfCr8cMFCZxEF1 xZaXS63JJ9XH0l0tpd1hbTvzTme3q9sfVnaee0QsZPWZddF2ad3KRzWsH8Gum6dfePQFsRFQ6mlB zUcD2Hr7xnT09yFnQFJxCvisooqZhF7BPCvJiFrUcY39yIdmUqPqK10cAtvECjgdqQlGfLjF6nVx Uxm0NOoQhkrjNZ2exvDyKQtbKat5FNlBIqqcoCLVstjxGB9YIyrFKPhP9vHCeofzecLLyU6SRD2c wwyVKTMKzdza5LYh.04N9B0adVgXyssEoY7fO0VLKSZjP7Vg.obmFpUFe8gj4VWeLuBGh7dkQDCH 8O_dQdmgfSMXTceh.VwFCxaDnGC2hIXOgqURS_VYOeAM8AIds0UcOjp7NRCvIStERLJ1rHgHl.5R _WFzFgmLmSS7REzP0e3DTqdt7x26_stQw.SRqZ6K5h5lAVvHmrNOciBng.QB1pco3HEgpUOZKdr4 bc8Yr0zj6.WK6LwC1zyVdFuHyhDxrbbHwPsSaHexi6SnNBMVz1aa89k6Ulnov2caUeFMN7k433w0 8K0rIIMdAPSjkZ0b6XdR09U7ns5AejW7Nw0F9qbxSSO3Y1NpLDN2BRCeQaS9ntP5bHLCnokVoJCi KWlStvrtxF6nDltXOqAL5pgEn1I3ROtNjcWXoOXmUe_sqqkRLwan_zK16_oe0KKxWvtvW5N.q_0O Tt_Wt66sr3ZhDQAa6eN8taCofn90rUBSk4Tp2MOAqhQp2zKD7sPOB3IYMV5aUiMVjYYzkSym6FkW bPJifS1SJFF9CAAHKg0QK35aIpJrsaju0VJNgcXSlWd6I2fa3WrYjwDQ6MuJ70u5KUQFCGSHS5go IarqBD4Wqh48L1ct07pb_tzsgmuWaC3e_R3UeFjw5oHmtvetScfdzpyBzOEOxVpQnrh7kDuQfl1e nHOtz0_RtZ7jmfkO9FeZe_ZSsF7NqKTrzPPvSMnKT3gVBLnebr5n9EIwSdk.UGHSWaNx9Rbe8dKy FSWElPjmn_wIzYCZzeM1JTL5uVLGlv50_4jgEOGexyeV3rxw51BXxrgpa..FSUrHv.HP0rnfnhEq YvFVP7hHjbW2A5MJJja3FssVubG_tVUHeub3FKIXteOC.0MJufdMMyh.E34WI9ywRLJPt1nD.cAb eVn_cwIH7O01.KF1ZFgY8u1YQnN4bxz8CLFykdVMWammXpyFUPlXSkBXu6dbjWVCUq_X_9u9fs_9 ixKRRXsS5f_Q1XMbHc.KVsc7kIZRUQwEp1R1Am3pPSWptP623AFNLdHDNdmmL3neDoqdJ_Uj371k aA4_.M5B_Divfl.jkU.fYL11tzSpwpjC4HRN8nj77gVclqk9ijfW22IWHuiyEC30tx_M2kmig3Ta BlFiaaUbXQdCHTUDsJ9Lw9l79jJu2F6_0tAchc1gsDq1VrHPRXuJ42F9qsIZzpOG7.sohyLWvpft J5WDJL7wjPsS5EKqSSZxZq9ik1a.1sTuka3TFfsOq3xwumb3Nw5rM_LZUfddchmmX4QcKcqWTELk WWVacLMpBjL.pdcNgYtOUAKzr6gILzN_Be6v.WVZh5V7Hxt2CUUJWXg9hXvWpPdAhF1H9xP8ZsCJ Sn3bamftnMhiGbNfxrumSWBtPUvNIXMTWdK47z_Z7bdMlJt935X1e9g_3S1fOYAPf4mQMQJipoKC ON37u2hwvrSHZKEAZpY8cyByk2cTHE_F.FkbfYbHA_9GtgjoIc5.8PMbIn1RQsGLjnQ0GvxDtMju ehJQHOLtDgQIk3v7hqKSG7HH7UoGsOW4Xq8TABnQnznTQ539TnMhuRwoThO10lzRbYFG8yp.36lC xQHroCLJ_pZYjhY8LZ9z2Os2AGRtEcx2bGFeKlPUCLa0fkzgCgg-- X-Sonic-MF: Received: from sonic.gate.mail.ne1.yahoo.com by sonic301.consmr.mail.gq1.yahoo.com with HTTP; Sat, 16 Apr 2022 04:44:11 +0000 Received: by hermes--canary-production-bf1-5f49dbcd6-7hbzw (VZM Hermes SMTP Server) with ESMTPA ID 09edd9fe64c919008b6ee70aa24dee8e; Sat, 16 Apr 2022 04:44:08 +0000 (UTC) Date: Sat, 16 Apr 2022 00:44:04 -0400 From: "Alex Xu (Hello71)" Subject: Non-zero RELA section contents To: binutils@sourceware.org, jbeulich@suse.com MIME-Version: 1.0 Message-Id: <1650070699.hyefqn4i18.none@localhost> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable References: <1650070699.hyefqn4i18.none.ref@localhost> X-Mailer: WebService/1.1.20048 mail.backend.jedi.jws.acl:role.jedi.acl.token.atz.jws.hermes.yahoo X-Spam-Status: No, score=-12.0 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, GIT_PATCH_0, RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H2, SPF_HELO_NONE, SPF_PASS, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: binutils@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Binutils mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 16 Apr 2022 04:44:14 -0000 Hi, In ELF RELA relocations, the addend is stored in the relocation instead=20 of the section contents. This was the premise of commit 17c6c3b99156=20 ("x86-64/ELF: clear src_mask for all reloc types"); the value in the=20 section contents is not used. I recently encountered a difficult-to-trace bug in 7-Zip, eventually=20 determined to be caused by JWasm-family assemblers incorrectly putting=20 the addend in the section contents, and setting the RELA addend to -4.=20 Previous versions of binutils added the existing value to the relocation=20 result, producing a working program; new versions of binutils overwrite=20 it, producing a non-working program. Now, I want to be clear: while the relevant specifications are not clear=20 about what the linker should do in this case, they are reasonably clear=20 that the assembler should not generate this. The assembler is absolutely=20 wrong. With that being said, I think it would be a good idea for ld to either=20 revert to the previous behavior or issue a warning or error when=20 detecting such malformed object files. I think a warning at the least is=20 appropriate, because binaries are either silently incorrect on the old=20 version, or silently incorrect on the new version, and silently=20 incorrect relocations are extremely hard to diagnose. One argument in=20 favor of reverting to the previous behavior is it is better to preserve=20 backwards compatibility in BFD linker when the new behavior is not=20 clearly superior (e.g. faster or closer to spec). One argument in favor=20 of the new behavior is that it is consistent with LLD and probably gold. The following patch adds a warning: diff --git a/bfd/reloc.c b/bfd/reloc.c index 5098e0ab09f..aecdb21ec59 100644 --- a/bfd/reloc.c +++ b/bfd/reloc.c @@ -1509,6 +1509,11 @@ _bfd_relocate_contents (reloc_howto_type *howto, relocation >>=3D (bfd_vma) rightshift; relocation <<=3D (bfd_vma) bitpos; =20 + if (!howto->src_mask && (x & howto->dst_mask)) + _bfd_error_handler + (_("warning: %pB: existing value for %s relocation is %lx, expected = 0"), + input_bfd, howto->name, x); + /* Add RELOCATION to the right bits of X. */ x =3D ((x & ~howto->dst_mask) | (((x & howto->src_mask) + relocation) & howto->dst_mask)); I have tested this patch on a single test file which printed the desired=20 warning. I believe %lx is probably wrong, but I don't know how to fix=20 it. I suspect this patch may cause a large number of warnings in certain=20 cases; however, I think adding a warning here is valid, because the=20 result is either broken with old binutils or broken with new binutils=20 (or both), and furthermore, proper assemblers should never generate this=20 case in the first place. I think the primary counterargument is that the point of "either broken=20 with old binutils or broken with new binutils" primarily applies to=20 x86-64/ELF, and may not apply to other targets. I am insufficiently=20 familiar with other targets to say whether this is the case. If so, it=20 may be better to add this warning only for x86-64/ELF. Thanks, Alex.