From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2001:4830:2446:ff00:4687:fcff:fea6:5117]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id E7B852C007E for ; Tue, 14 May 2013 16:59:24 +1000 (EST) Message-ID: <1368514745.3490.10.camel@shinybook.infradead.org> Subject: Re: [PATCH] powerpc: provide __bswapdi2 From: David Woodhouse To: Michael Neuling Date: Tue, 14 May 2013 07:59:05 +0100 In-Reply-To: References: <1368220707.3378.57.camel@shinybook.infradead.org> <9813.1368428999@ale.ozlabs.ibm.com> <20130514110924.091b7177d22d69e19478a134@canb.auug.org.au> Content-Type: multipart/signed; micalg="sha1"; protocol="application/x-pkcs7-signature"; boundary="=-7rmV8jDvnwymPWDzoBze" Mime-Version: 1.0 Cc: Stephen Rothwell , viro@zeniv.linux.org.uk, Linux PPC dev List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , --=-7rmV8jDvnwymPWDzoBze Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, 2013-05-14 at 11:25 +1000, Michael Neuling wrote: >=20 > > So, if we are just stealing the output of gcc, why not just use the C > > version (at least for 32 bit)? >=20 > Woodhouse: can we just do this? Sure, if you don't mind GCC optimising the contents of your C function by turning it into a call to libgcc's __bswapdi2() :) OK, you might be able to do some archaeology and determine that the only compiler that emits calls to __bswapdi2() is GCC 4.4, and furthermore that the same compiler *doesn't* have the wit to notice that the contents of the function are a 64-bit byteswap, so it's never going to happen. But I don't like that approach. I'd feel I have to sacrifice a goat *anyway*, and I don't have a spare goat. Although now I come to explicitly explain why I did it that way... it occurs to me that the libgcc version is just written in C, and the compiler evidently trusts itself not to optimise that into a recursive call. Is there a compiler switch which guarantees that, which we could use without other unwanted side-effects? =20 --=20 David Woodhouse Open Source Technology Centre David.Woodhouse@intel.com Intel Corporation --=-7rmV8jDvnwymPWDzoBze Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGSIb3DQEHAQAAoIISxDCCBjQw ggQcoAMCAQICAR4wDQYJKoZIhvcNAQEFBQAwfTELMAkGA1UEBhMCSUwxFjAUBgNVBAoTDVN0YXJ0 Q29tIEx0ZC4xKzApBgNVBAsTIlNlY3VyZSBEaWdpdGFsIENlcnRpZmljYXRlIFNpZ25pbmcxKTAn BgNVBAMTIFN0YXJ0Q29tIENlcnRpZmljYXRpb24gQXV0aG9yaXR5MB4XDTA3MTAyNDIxMDE1NVoX DTE3MTAyNDIxMDE1NVowgYwxCzAJBgNVBAYTAklMMRYwFAYDVQQKEw1TdGFydENvbSBMdGQuMSsw KQYDVQQLEyJTZWN1cmUgRGlnaXRhbCBDZXJ0aWZpY2F0ZSBTaWduaW5nMTgwNgYDVQQDEy9TdGFy dENvbSBDbGFzcyAxIFByaW1hcnkgSW50ZXJtZWRpYXRlIENsaWVudCBDQTCCASIwDQYJKoZIhvcN AQEBBQADggEPADCCAQoCggEBAMcJg8zOLdgasSmkLhOrlr6KMoOMpohBllVHrdRvEg/q6r8jR+EK 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