From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753356AbbDHMGM (ORCPT ); Wed, 8 Apr 2015 08:06:12 -0400 Received: from mail-ig0-f177.google.com ([209.85.213.177]:35154 "EHLO mail-ig0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752001AbbDHMGK (ORCPT ); Wed, 8 Apr 2015 08:06:10 -0400 Message-ID: <552519AF.1060201@gmail.com> Date: Wed, 08 Apr 2015 08:06:07 -0400 From: Austin S Hemmelgarn User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 MIME-Version: 1.0 To: Pengfei Yuan <0xcoolypf@gmail.com> CC: Mike Galbraith , linux-kernel@vger.kernel.org Subject: Re: Why not build kernel with -O3 References: <1428388995.3152.10.camel@gmail.com> <1428401356.3152.38.camel@gmail.com> <55241C51.8040107@gmail.com> In-Reply-To: x-hashcash: 1:21:150408:0xcoolypf@gmail.com::e4571b3439368d3a808a5d40c903a773:903a8b89cc666a02 x-hashcash: 1:21:150408:umgwanakikbuti@gmail.com::83648b9a34cd6001bbb19150ff4439fe:e65cb5eb34296182 x-hashcash: 1:21:150408:linux-kernel@vger.kernel.org::2531adddd12f3a4130403f666e9c46fc:84741211170ed55b x-stampprotocols: hashcash:1:17;mbound:0:10:3000:5000 Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha1; boundary="------------ms040503020202030802000302" X-Antivirus: avast! (VPS 150408-1, 2015-04-08), Outbound message X-Antivirus-Status: Clean Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is a cryptographically signed message in MIME format. --------------ms040503020202030802000302 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 2015-04-07 21:00, Pengfei Yuan wrote: > Could you please provide some examples that I can investigate? > Thanks! > > 2015-04-08 2:05 GMT+08:00 Austin S Hemmelgarn : >> On 2015-04-07 06:09, Mike Galbraith wrote: >>> On Tue, 2015-04-07 at 15:56 +0800, Pengfei Yuan wrote: >>>> I am trying legacy GCC versions. >>>> But I am not able to try different architectures. >>> >>> The point of my reply wasn't to get you to actually test the world ;-= ) >>> >>> I was indirectly pointing out that "works for me" is not good enough >>> justification. Much checking for safety/benefit required. >>> >> Safety especially, -O3 is known to cause perfectly standards-compliant= >> code to break in weird ways in user-space. >> >> I can't remember any off the top of my head, but it does say explicitly=20 in the GCC manual to be careful with -O3. IIRC, most of the issues=20 relate to -O3 enabling -ffast-math (which tends to really mess with code = that expects strict IEEE 754 compliance), so it may not be as much of an = issue for kernel code. You might look into some of the projects that=20 use -O3 by default (I think most of the Mozilla so0ftware does these=20 days, and I know that there are others, I just can't remember what right = now). --------------ms040503020202030802000302 Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="smime.p7s" Content-Description: S/MIME Cryptographic Signature MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGSIb3DQEHAQAAoIIGuDCC BrQwggScoAMCAQICAxBuVTANBgkqhkiG9w0BAQ0FADB5MRAwDgYDVQQKEwdSb290IENBMR4w HAYDVQQLExVodHRwOi8vd3d3LmNhY2VydC5vcmcxIjAgBgNVBAMTGUNBIENlcnQgU2lnbmlu ZyBBdXRob3JpdHkxITAfBgkqhkiG9w0BCQEWEnN1cHBvcnRAY2FjZXJ0Lm9yZzAeFw0xNTAz MjUxOTM0MzhaFw0xNTA5MjExOTM0MzhaMGMxGDAWBgNVBAMTD0NBY2VydCBXb1QgVXNlcjEj MCEGCSqGSIb3DQEJARYUYWhmZXJyb2luN0BnbWFpbC5jb20xIjAgBgkqhkiG9w0BCQEWE2Fo ZW1tZWxnQG9oaW9ndC5jb20wggIiMA0GCSqGSIb3DQEBAQUAA4ICDwAwggIKAoICAQCdD/zW 2rRAFCLnDfXpWxU1+ODqRVUgzHvrRO7ADUxRo1CBDc3JSX5TIW2OGmQ3DAKGOACp8Z0sgxMc B05tzAZ/M7m4jajVrwwdVCdrwVGxTdAai7Kwg4ZCVfyMVhcwo8R2eW3QahBx34G0RKumK9sZ ZQSQ+zULAzpY6uz7T1sAk/erMoivRXF6u8WvOsLkOD1F/Xyv1ZccSUG5YeDgZgc0nZUBvyIp zXSHjgWerFkrxEM3y2z/Ff3eL1sgGYecV/I1F+I5S01V7Kclt/qRW10c/4JEGRcI1FmrJBPu BtMYPbg/3Y9LZROYN+mVIFxZxOfrmjfFZ96xt/TaMXo8vcEKtWcNEjhGBjEbfMUEm4aq8ygQ 4MuEcpJc8DJCHBkg2KBk13DkbU2qNepTD6Uip1C+g+KMr0nd6KOJqSH27ZuNY4xqV4hIxFHp ex0zY7mq6fV2o6sKBGQzRdI20FDYmNjsLJwjH6qJ8laxFphZnPRpBThmu0AjuBWE72GnI1oA aO+bs92MQGJernt7hByCnDO82W/ykbVz+Ge3Sax8NY0m2Xdvp6WFDY/PjD9CdaJ9nwQGsUSa N54lrZ2qMTeCI9Vauwf6U69BA42xgk65VvxvTNqji+tZ4aZbarZ7el2/QDHOb/rRwlCFplS/ z4l1f1nOrE6bnDl5RBJyW3zi74P6GwIDAQABo4IBWTCCAVUwDAYDVR0TAQH/BAIwADBWBglg hkgBhvhCAQ0ESRZHVG8gZ2V0IHlvdXIgb3duIGNlcnRpZmljYXRlIGZvciBGUkVFIGhlYWQg b3ZlciB0byBodHRwOi8vd3d3LkNBY2VydC5vcmcwDgYDVR0PAQH/BAQDAgOoMEAGA1UdJQQ5 MDcGCCsGAQUFBwMEBggrBgEFBQcDAgYKKwYBBAGCNwoDBAYKKwYBBAGCNwoDAwYJYIZIAYb4 QgQBMDIGCCsGAQUFBwEBBCYwJDAiBggrBgEFBQcwAYYWaHR0cDovL29jc3AuY2FjZXJ0Lm9y ZzAxBgNVHR8EKjAoMCagJKAihiBodHRwOi8vY3JsLmNhY2VydC5vcmcvcmV2b2tlLmNybDA0 BgNVHREELTArgRRhaGZlcnJvaW43QGdtYWlsLmNvbYETYWhlbW1lbGdAb2hpb2d0LmNvbTAN BgkqhkiG9w0BAQ0FAAOCAgEAGvl7xb42JMRH5D/vCIDYvFY3dR2FPd5kmOqpKU/fvQ8ovmJa p5N/FDrsCL+YdslxPY+AAn78PYmL5pFHTdRadT++07DPIMtQyy2qd+XRmz6zP8Il7vGcEDmO WmMLYMq4xV9s/N7t7JJp6ftdIYUcoTVChUgilDaRWMLidtslCdRsBVfUjPb1bF5Ua31diKDP e0M9/e2CU36rbcTtiNCXhptMigzuL3zJXUf2B9jyUV8pnqNEQH36fqJ7YTBLcpq3aYa2XbAH Hgx9GehJBIqwspDmhPCFZ/QmqUXCkt+XfvinQ2NzKR6P3+OdYbwqzVX8BdMeojh7Ig8x/nIx mQ+/ufstL1ZYp0bg13fyK/hPYSIBpayaC76vzWovkIm70DIDRIFLi20p/qTd7rfDYy831Hjm +lDdCECF9bIXEWFk33kA97dgQIMbf5chEmlFg8S0e4iw7LMjvRqMX3eCD8GJ2+oqyZUwzZxy S0Mx+rBld5rrN7LsXwZ671HsGqNeYbYeU25e7t7/Gcc6Bd/kPfA+adEuUGFcvUKH3trDYqNq 6mOkAd8WO/mQadlc3ztS++XDMhmIpfBre9MPAr6usqf+wc+R8Nk9KLK39kEgrqVfzc/fgf8L MaD4rHnusdg4gca6Yi+kNrm99anw7SwaBrBvULYBp7ixNRUhaYiNW4YjTrYxggShMIIEnQIB ATCBgDB5MRAwDgYDVQQKEwdSb290IENBMR4wHAYDVQQLExVodHRwOi8vd3d3LmNhY2VydC5v cmcxIjAgBgNVBAMTGUNBIENlcnQgU2lnbmluZyBBdXRob3JpdHkxITAfBgkqhkiG9w0BCQEW EnN1cHBvcnRAY2FjZXJ0Lm9yZwIDEG5VMAkGBSsOAwIaBQCgggH1MBgGCSqGSIb3DQEJAzEL BgkqhkiG9w0BBwEwHAYJKoZIhvcNAQkFMQ8XDTE1MDQwODEyMDYwN1owIwYJKoZIhvcNAQkE MRYEFOwOAG19I7FnL+qtlxgLSsh16itIMGwGCSqGSIb3DQEJDzFfMF0wCwYJYIZIAWUDBAEq MAsGCWCGSAFlAwQBAjAKBggqhkiG9w0DBzAOBggqhkiG9w0DAgICAIAwDQYIKoZIhvcNAwIC AUAwBwYFKw4DAgcwDQYIKoZIhvcNAwICASgwgZEGCSsGAQQBgjcQBDGBgzCBgDB5MRAwDgYD VQQKEwdSb290IENBMR4wHAYDVQQLExVodHRwOi8vd3d3LmNhY2VydC5vcmcxIjAgBgNVBAMT GUNBIENlcnQgU2lnbmluZyBBdXRob3JpdHkxITAfBgkqhkiG9w0BCQEWEnN1cHBvcnRAY2Fj ZXJ0Lm9yZwIDEG5VMIGTBgsqhkiG9w0BCRACCzGBg6CBgDB5MRAwDgYDVQQKEwdSb290IENB MR4wHAYDVQQLExVodHRwOi8vd3d3LmNhY2VydC5vcmcxIjAgBgNVBAMTGUNBIENlcnQgU2ln bmluZyBBdXRob3JpdHkxITAfBgkqhkiG9w0BCQEWEnN1cHBvcnRAY2FjZXJ0Lm9yZwIDEG5V MA0GCSqGSIb3DQEBAQUABIICAIC5LwheqfbgSySmgaNRoZTtmy3R/BWglX4QJCLNbSYfljXy I+ozfpluKF+9BbPunsnj+9GZVqMAUJVgUaM2hl2CGMcfcPt0mDO02UapfYBBRdkilCblPTen lYJM53JNX3j41MWkG9bqOjjf1JdjbB2F8EUHcceqPXtiSVICTHMDg9kiVkeQWR7Vep7TwSuP pEKMus1BxFXBiOTo8TgUkxVzlOkPlLBC3OB/hKuYUt7TQGpaQNENT/mcIAileNsqYjvLtQ0r yNjvSX1+kJKN5R3Wj71FMnbsOHbUZm8ytdrmPG7/QBzgc34lWofxp4VbJhGFe7OEI8t5EA8B cgxazrhTRIPbwVVjbjwKYq2tmyRFH4/TSut+1DnJsYiNqdFcxUG5RNObHg7hdY2VokRpznjr QMdfO6u67Z3tiHtYW0SNz0pLL5Ge1EcyKHi2fszepvuhZ6vC2uf9Y30SlBsue2qLG5QBOiyz a6JWHGzypRLoDKRzuJsiBuX0ILwWrvVJhEnbdzdJvlqxtrnIRs+KNhhTnfBMOohnXyrE7hI6 OcJCan9ghMaUcp44jgnFs7ZD5qtacAn8u2O/r7yhf+Jp5Xb+5I4HB+Vu0jUs5Xl3ASvQ1SGD M1c0c9B/xeyCGBGg5119hYe2/lkd/u3PpMOWFVeReumGeeWsUDye4b3POgrcAAAAAAAA --------------ms040503020202030802000302--