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=-17.4 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_IN_DEF_DKIM_WL 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 1CA5CC433E7 for ; Mon, 19 Oct 2020 19:24:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id ACB2522283 for ; Mon, 19 Oct 2020 19:24:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="ju2ohyzm" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730932AbgJSTYQ (ORCPT ); Mon, 19 Oct 2020 15:24:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59786 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730845AbgJSTYQ (ORCPT ); Mon, 19 Oct 2020 15:24:16 -0400 Received: from mail-pl1-x643.google.com (mail-pl1-x643.google.com [IPv6:2607:f8b0:4864:20::643]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A8FA1C0613CE for ; Mon, 19 Oct 2020 12:24:14 -0700 (PDT) Received: by mail-pl1-x643.google.com with SMTP id r10so302948plx.3 for ; Mon, 19 Oct 2020 12:24:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=uIfWuzz/Oi2OkmAg7QQj+om01xgjYQC13tivpsY4ap0=; b=ju2ohyzmil762bBA/+brUwTLU43sMSwJMV0FhC8+6ixcmC2U/oxWhswQCiDoLgBTUq p38dzwpBKwDZa/efpZvK4m6WhqPMHbQ2nXWl6u+aLkz1P1YvH2ZTBMGTYtlij0fGVrR1 8/4wmK5ZOlv3i1Wo/uWqlSeTjUL8TPN+LYBhvCcT+4ll1YeCG4PA5efit4fMi7TBt36X 446mVLHBrmxiOeOxV3oXOWdivJ5xLjlSbBhAidBizfZ88KKnU02l2rj8QkkZBYdfpXMO V9o0f74EhHJEqH7/ORiwM5hXl41CnZyh2cXElz3eU497i0hMHhN0wQhJHKmr9CwS/VwY thnQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=uIfWuzz/Oi2OkmAg7QQj+om01xgjYQC13tivpsY4ap0=; b=OsMFV5mRiNv3/iY+JTQ6P5OWJmI16ByK5CEsl0Ow7NIdRq33Q4tyVF1psa4rJTcfUo 0I3qUjfjeDvB6ggLZROcD7QP6wtj+0jBtkyGdRYBsan0FqHCcjCoTKotASkO50uerXTY xx2RWJ1i572Bw2Cj4ssOjMRw+PPtwEej+E7skNLgynrHEv2hNM7V9hgu6ux/8aNphjJT 39o9XDS2NQS6CmVq7LYk3qvG5WvfLevFhTKnYl25v3mmBkNW2ibHNg/L7iMC7PZStkRM G7KgHo3l1VRe0HtjVJzowsHi9yxy5vIapotwUN7dFSHEgJtsd3Glb8XjjoSGAqKX9WK4 P8Hg== X-Gm-Message-State: AOAM531zYCBAG5o7KjFSmNlO3QFPV7j4eYe5zfCiuUV+zYe8VOebr7GW 7bg28pAj5wWVfV5qS6k0JFBlCMsLRvamuPJiOmrYhQ== X-Google-Smtp-Source: ABdhPJwkm9qKOonfmzQG2CiafojX189ed37IunFvJ5nWQQY16dHeLxrFVDxkHYRel+Q/LZos+oZFpTmwL6ODbB6paFw= X-Received: by 2002:a17:902:c40b:b029:d3:def2:d90f with SMTP id k11-20020a170902c40bb02900d3def2d90fmr1361931plk.29.1603135453759; Mon, 19 Oct 2020 12:24:13 -0700 (PDT) MIME-Version: 1.0 References: <20201017002500.503011-1-palmerdabbelt@google.com> In-Reply-To: <20201017002500.503011-1-palmerdabbelt@google.com> From: Nick Desaulniers Date: Mon, 19 Oct 2020 12:24:02 -0700 Message-ID: Subject: Re: [PATCH] RISC-V: Fix the VDSO symbol generaton for binutils-2.34+ To: Palmer Dabbelt Cc: linux-riscv@lists.infradead.org, kernel-team , "# 3.4.x" , clang-built-linux Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Fri, Oct 16, 2020 at 5:44 PM 'Palmer Dabbelt' via Clang Built Linux wrote: > > We were relying on GNU ld's ability to re-link executable files in order > to extract our VDSO symbols. This behavior was deemed a bug as of > binutils-2.34 (specifically the binutils-gdb commit a87e1817a4 ("Have > the linker fail if any attempt to link in an executable is made."), > which IIUC landed in 2.34), which recently installed itself on my build > setup. > > The previous version of this was a bit of a mess: we were linking a > static executable version of the VDSO, containing only a subset of the > input symbols, which we then linked into the kernel. This worked, but > certainly wasn't a supported path through the toolchain. Instead this > new version parses the textual output of nm to produce a symbol table. > Both rely on near-zero addresses being linkable, but as we rely on weak > undefined symbols being linkable elsewhere I don't view this as a major > issue. > > Fixes: e2c0cdfba7f6 ("RISC-V: User-facing API") > Cc: stable@vger.kernel.org > Cc: clang-built-linux@googlegroups.com > Signed-off-by: Palmer Dabbelt Ah, I do see a build failure to link the vdso with: $ riscv64-linux-gnu-ld --version GNU ld (GNU Binutils for Debian) 2.34.90.20200706 riscv64-linux-gnu-ld: cannot use executable file 'arch/riscv/kernel/vdso/vdso-dummy.o' as input to a link This patch fixes that for me, but there's a problem related to related to `nm` below. After this, there's two other things we might want to fix up related to the build of the vdso: 1. it looks like $(CC) is being used to link the vdso, rather than $(LD). While it's generally fine to use the compiler as the driver for building a linked object file, it does not respect the set $(LD). `-fuse-ld=` needs to be passed to invoke the linker the user specified. See also: https://lore.kernel.org/linux-kbuild/20201013033947.2257501-1-natechancellor@gmail.com/T/#u (this has popped up in a few places when trying to do hermetic builds with LLD). 2. I observe the warning when building with clang: `argument unused during compilation: '-no-pie' [-Wunused-command-line-argument]`. IIRC, the top level Makefile sets `-Qunused-arguments` for builds with clang. `cmd_vdsold` may need that, but it's curious why it's unused and makes me wonder why/if `-no-pie` is necessary? That also might be fixed by fixing 1. > --- > arch/riscv/kernel/vdso/.gitignore | 1 + > arch/riscv/kernel/vdso/Makefile | 19 +++++++++---------- > arch/riscv/kernel/vdso/so2s.sh | 7 +++++++ > 3 files changed, 17 insertions(+), 10 deletions(-) > create mode 100755 arch/riscv/kernel/vdso/so2s.sh > > diff --git a/arch/riscv/kernel/vdso/.gitignore b/arch/riscv/kernel/vdso/.gitignore > index 11ebee9e4c1d..3a19def868ec 100644 > --- a/arch/riscv/kernel/vdso/.gitignore > +++ b/arch/riscv/kernel/vdso/.gitignore > @@ -1,3 +1,4 @@ > # SPDX-License-Identifier: GPL-2.0-only > vdso.lds > *.tmp > +vdso-syms.S > diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile > index 478e7338ddc1..2e02958f6224 100644 > --- a/arch/riscv/kernel/vdso/Makefile > +++ b/arch/riscv/kernel/vdso/Makefile > @@ -43,19 +43,14 @@ $(obj)/vdso.o: $(obj)/vdso.so > SYSCFLAGS_vdso.so.dbg = $(c_flags) > $(obj)/vdso.so.dbg: $(src)/vdso.lds $(obj-vdso) FORCE > $(call if_changed,vdsold) > +SYSCFLAGS_vdso.so.dbg = -shared -s -Wl,-soname=linux-vdso.so.1 \ > + -Wl,--build-id -Wl,--hash-style=both > > # We also create a special relocatable object that should mirror the symbol > # table and layout of the linked DSO. With ld --just-symbols we can then > # refer to these symbols in the kernel code rather than hand-coded addresses. > - > -SYSCFLAGS_vdso.so.dbg = -shared -s -Wl,-soname=linux-vdso.so.1 \ > - -Wl,--build-id -Wl,--hash-style=both > -$(obj)/vdso-dummy.o: $(src)/vdso.lds $(obj)/rt_sigreturn.o FORCE > - $(call if_changed,vdsold) > - > -LDFLAGS_vdso-syms.o := -r --just-symbols > -$(obj)/vdso-syms.o: $(obj)/vdso-dummy.o FORCE > - $(call if_changed,ld) > +$(obj)/vdso-syms.S: $(obj)/vdso.so FORCE > + $(call if_changed,so2s) > > # strip rule for the .so file > $(obj)/%.so: OBJCOPYFLAGS := -S > @@ -68,11 +63,15 @@ $(obj)/%.so: $(obj)/%.so.dbg FORCE > # Make sure only to export the intended __vdso_xxx symbol offsets. > quiet_cmd_vdsold = VDSOLD $@ > cmd_vdsold = $(CC) $(KBUILD_CFLAGS) $(call cc-option, -no-pie) -nostdlib -nostartfiles $(SYSCFLAGS_$(@F)) \ > - -Wl,-T,$(filter-out FORCE,$^) -o $@.tmp && \ > + -Wl,-T,$(filter-out FORCE,$^) -o $@.tmp -Wl,-Map,$@.map && \ > $(CROSS_COMPILE)objcopy \ > $(patsubst %, -G __vdso_%, $(vdso-syms)) $@.tmp $@ && \ > rm $@.tmp > > +# Extracts > +quiet_cmd_so2s = SO2S $@ > + cmd_so2s = $(CROSS_COMPILE)nm -D $< | $(src)/so2s.sh > $@ This should use `$(NM)` rather than `$(CROSS_COMPILE)nm` which hardcodes the use of GNU nm from GNU binutils. > + > # install commands for the unstripped file > quiet_cmd_vdso_install = INSTALL $@ > cmd_vdso_install = cp $(obj)/$@.dbg $(MODLIB)/vdso/$@ > diff --git a/arch/riscv/kernel/vdso/so2s.sh b/arch/riscv/kernel/vdso/so2s.sh > new file mode 100755 > index 000000000000..7862866b5ebb > --- /dev/null > +++ b/arch/riscv/kernel/vdso/so2s.sh > @@ -0,0 +1,6 @@ > +#!/bin/sh > +# SPDX-License-Identifier: GPL-2.0+ > +# Copyright 2020 Palmer Dabbelt > + > +sed 's!\([0-9a-f]*\) T \([a-z0-9_]*\)@@LINUX_4.15!.global \2\n.set \2,0x\1!' \ > +| grep '^\.' > -- -- Thanks, ~Nick Desaulniers