From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 39DCEC43381 for ; Fri, 15 Mar 2019 23:34:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C61DC218AC for ; Fri, 15 Mar 2019 23:34:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="LTOACvOY" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727487AbfCOXeN (ORCPT ); Fri, 15 Mar 2019 19:34:13 -0400 Received: from mail-pf1-f194.google.com ([209.85.210.194]:44336 "EHLO mail-pf1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726744AbfCOXeM (ORCPT ); Fri, 15 Mar 2019 19:34:12 -0400 Received: by mail-pf1-f194.google.com with SMTP id a3so7347013pff.11 for ; Fri, 15 Mar 2019 16:34:12 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=/ir9ttkQ1CiAYtX6fgzXb09UuqQKWka5j2fxnc9hcEA=; b=LTOACvOYK6zESiQl66UnQ7DJc0XVFk2W+3ZcWB0Rh5WH/NZvLmNXRpPSWBOichAnoP 2g0hZZWnrbv9wUk+S42xYS8fPkr32T4J4usvDl87PgtB0bzJvFEx0/lR5GTwv8vOFyiI MI3X7kDKSITArWLq2tH+sY5cCdth29IadZSMM= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=/ir9ttkQ1CiAYtX6fgzXb09UuqQKWka5j2fxnc9hcEA=; b=GTX8wy11gOehQqgS+57iVgZ8WTuKL7Oajy/v4mFiiZDV0iwu77VRJqv2jDw2pUzBmS 7bhTON0icqWJmOjYsCVVCu5CSRdolAlQGjDW9jtMv2CMXWuwbNK/j1+q5qqoxGtSoxlL KhV9mQoIpC9SMpBrTxQD/Fmy1G/ELFkVZSA6ukepV+qWBmnAe6MpNFeLu48Cf7ZU3nxd qbsnXvBffGRiA5KGz8869Y30FhcK47BygkovyTsXEmU2SCiM71ZpegJmFQOeEaIAjkx3 /l0ZHA42VXzf5J/riR5FufSH+ONIQLUuRL/T/UExxJArH8dRh9ptuAjm+OcCafAj2KOU L7uA== X-Gm-Message-State: APjAAAVdI/UZ//g0KSsyHWspsxtOmX/fTw2TXxdoyEMI6UyZYieqGAO+ 9+wAvFJzJf61pD60D7+2Uysrrg== X-Google-Smtp-Source: APXvYqzso6tZ3hLHXqe337MC2CP8eYYa3qyuTeXpVi7bJB0rvs89dMhkDiLAQYAUc6DUIdL3rYiBUg== X-Received: by 2002:a63:e654:: with SMTP id p20mr5953582pgj.345.1552692851693; Fri, 15 Mar 2019 16:34:11 -0700 (PDT) Received: from localhost ([2620:15c:202:1:75a:3f6e:21d:9374]) by smtp.gmail.com with ESMTPSA id e8sm4101829pfn.103.2019.03.15.16.34.10 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 15 Mar 2019 16:34:11 -0700 (PDT) Date: Fri, 15 Mar 2019 16:34:10 -0700 From: Matthias Kaehlcke To: hpa@zytor.com Cc: Nick Desaulniers , Andy Lutomirski , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, LKML , Manoj Gupta , Tiancong Wang , Stephen Hines , clang-built-linux@googlegroups.com, Miguel Ojeda Subject: Re: [PATCH] lib: Add shared copy of __lshrti3 from libgcc Message-ID: <20190315233410.GE112750@google.com> References: <9C4AC321-B808-40B4-B16A-B3E28DFA3591@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <9C4AC321-B808-40B4-B16A-B3E28DFA3591@zytor.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Peter, On Fri, Mar 15, 2019 at 03:08:57PM -0700, hpa@zytor.com wrote: > On March 15, 2019 3:06:37 PM PDT, Nick Desaulniers wrote: > >On Fri, Mar 15, 2019 at 1:54 PM Matthias Kaehlcke > >wrote: > >> > >> The compiler may emit calls to __lshrti3 from the compiler runtime > >> library, which results in undefined references: > >> > >> arch/x86/kvm/x86.o: In function `mul_u64_u64_shr': > >> include/linux/math64.h:186: undefined reference to `__lshrti3' > > > >Looks like Clang will emit this at -Oz (but not -O2): > >https://godbolt.org/z/w1_2YC > > > >> > >> Add a copy of the __lshrti3 libgcc routine (from gcc v4.9.2). > > > >Has it changed since? If so why not a newer version of libgcc_s? > > > >> > >> Include the function for x86 builds with clang, which is the > >> environment where the above error was observed. > >> > >> Signed-off-by: Matthias Kaehlcke > >> --- > >> arch/x86/Kconfig | 1 + > >> include/linux/libgcc.h | 16 ++++++++++++++++ > >> lib/Kconfig | 3 +++ > >> lib/Makefile | 1 + > >> lib/lshrti3.c | 31 +++++++++++++++++++++++++++++++ > >> 5 files changed, 52 insertions(+) > >> create mode 100644 lib/lshrti3.c > >> > >> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > >> index c1f9b3cf437c..a5e0d923845d 100644 > >> --- a/arch/x86/Kconfig > >> +++ b/arch/x86/Kconfig > >> @@ -105,6 +105,7 @@ config X86 > >> select GENERIC_IRQ_PROBE > >> select GENERIC_IRQ_RESERVATION_MODE > >> select GENERIC_IRQ_SHOW > >> + select GENERIC_LIB_LSHRTI3 if CC_IS_CLANG > >> select GENERIC_PENDING_IRQ if SMP > >> select GENERIC_SMP_IDLE_THREAD > >> select GENERIC_STRNCPY_FROM_USER > >> diff --git a/include/linux/libgcc.h b/include/linux/libgcc.h > >> index 32e1e0f4b2d0..a71036471838 100644 > >> --- a/include/linux/libgcc.h > >> +++ b/include/linux/libgcc.h > >> @@ -22,15 +22,26 @@ > >> #include > >> > >> typedef int word_type __attribute__ ((mode (__word__))); > >> +typedef int TItype __attribute__ ((mode (TI))); > > > >Well that's an interesting new compiler attribute. > >https://stackoverflow.com/questions/4559025/what-does-gcc-attribute-modexx-actually-do > >Please use `__mode(TI)` from include/linux/compiler_attributes.h ex. > >typedef int TItype __mode(TI); > > > >> > >> #ifdef __BIG_ENDIAN > >> struct DWstruct { > >> int high, low; > >> }; > >> + > >> +struct DWstruct128 { > >> + long long high, low; > >> +}; > >> + > >> #elif defined(__LITTLE_ENDIAN) > >> struct DWstruct { > >> int low, high; > >> }; > >> + > >> +struct DWstruct128 { > >> + long long low, high; > >> +}; > >> + > >> #else > >> #error I feel sick. > >> #endif > >> @@ -40,4 +51,9 @@ typedef union { > >> long long ll; > >> } DWunion; > >> > >> +typedef union { > >> + struct DWstruct128 s; > >> + TItype ll; > >> +} DWunion128; > >> + > >> #endif /* __ASM_LIBGCC_H */ > >> diff --git a/lib/Kconfig b/lib/Kconfig > >> index a9e56539bd11..369e10259ea6 100644 > >> --- a/lib/Kconfig > >> +++ b/lib/Kconfig > >> @@ -624,6 +624,9 @@ config GENERIC_LIB_ASHRDI3 > >> config GENERIC_LIB_LSHRDI3 > >> bool > >> > >> +config GENERIC_LIB_LSHRTI3 > >> + bool > >> + > >> config GENERIC_LIB_MULDI3 > >> bool > >> > >> diff --git a/lib/Makefile b/lib/Makefile > >> index 4e066120a0d6..42648411f451 100644 > >> --- a/lib/Makefile > >> +++ b/lib/Makefile > >> @@ -277,6 +277,7 @@ obj-$(CONFIG_PARMAN) += parman.o > >> obj-$(CONFIG_GENERIC_LIB_ASHLDI3) += ashldi3.o > >> obj-$(CONFIG_GENERIC_LIB_ASHRDI3) += ashrdi3.o > >> obj-$(CONFIG_GENERIC_LIB_LSHRDI3) += lshrdi3.o > >> +obj-$(CONFIG_GENERIC_LIB_LSHRTI3) += lshrti3.o > >> obj-$(CONFIG_GENERIC_LIB_MULDI3) += muldi3.o > >> obj-$(CONFIG_GENERIC_LIB_CMPDI2) += cmpdi2.o > >> obj-$(CONFIG_GENERIC_LIB_UCMPDI2) += ucmpdi2.o > >> diff --git a/lib/lshrti3.c b/lib/lshrti3.c > >> new file mode 100644 > >> index 000000000000..2d2123bb3030 > >> --- /dev/null > >> +++ b/lib/lshrti3.c > >> @@ -0,0 +1,31 @@ > >> +// SPDX-License-Identifier: GPL-2.0 > >> + > >> +#include > >> +#include > >> + > >> +long long __lshrti3(long long u, word_type b) > >> +{ > >> + DWunion128 uu, w; > >> + word_type bm; > >> + > >> + if (b == 0) > >> + return u; > >> + > >> + uu.ll = u; > >> + bm = 64 - b; > >> + > >> + if (bm <= 0) { > >> + w.s.high = 0; > >> + w.s.low = (unsigned long long) uu.s.high >> -bm; > >> + } else { > >> + const unsigned long long carries = > >> + (unsigned long long) uu.s.high << bm; > >> + w.s.high = (unsigned long long) uu.s.high >> b; > >> + w.s.low = ((unsigned long long) uu.s.low >> b) | > >carries; > >> + } > >> + > >> + return w.ll; > >> +} > >> +#ifndef BUILD_VDSO > >> +EXPORT_SYMBOL(__lshrti3); > >> +#endif > > > >I don't think you want this. Maybe that was carried over from > >https://lkml.org/lkml/2019/3/15/669 > >by accident? The above linkage error mentions arch/x86/kvm/x86.o > >which I wouldn't expect to be linked into the VDSO image? > > If we compile with the default ABI we can simply link with libgcc; > with -mregparm=3 all versions of gcc are broken. I suppose you refer to linking the VDSO against libgcc? Would this be acceptable (as opposed to linking the kernel against it)?