From patchwork Tue Apr 28 22:14:18 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Nathan Chancellor X-Patchwork-Id: 11515743 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 722EB92C for ; Tue, 28 Apr 2020 22:14:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 55DBC2076A for ; Tue, 28 Apr 2020 22:14:57 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="b/C9LOZ0" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726973AbgD1WOv (ORCPT ); Tue, 28 Apr 2020 18:14:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50698 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1726898AbgD1WOr (ORCPT ); Tue, 28 Apr 2020 18:14:47 -0400 Received: from mail-ot1-x344.google.com (mail-ot1-x344.google.com [IPv6:2607:f8b0:4864:20::344]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4999EC03C1AD; Tue, 28 Apr 2020 15:14:47 -0700 (PDT) Received: by mail-ot1-x344.google.com with SMTP id z17so35708450oto.4; Tue, 28 Apr 2020 15:14:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=5MojLeIiS5IJ/f4OVpVWsw3ucrS28qn0/t/fHk4cEKI=; b=b/C9LOZ0PhFIybMMzacd5jkAEASReFP1A6oZuZTQSOyUW3Rmvy9DQHjLXwFZeuCXnk 0BJ0VMqjzl9Xk5f2oxAjSrdEmTLnBq+ALBBSt2BVxDo7VBQg0s8rXXuVlE0AXpsfV2MB ho5HS+pfA3QlVD78R+8yFZCqYlDzjmFcyfdGzy6wuTY5Qy6P8H/xkYC/5dy1OlhImz4t sGgzeAzDB4LL3pEj2Er8/yymkukWJ+sPhJATj8Glt3etrKDxrLemxrR1GAyytutqhUHc RrOwosNmI0y8reCfHdOJjFudRuAYIlnETabEKhOUWXXu0l7jAcLUoDnVUdH7C4GFxJQz VbBA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=5MojLeIiS5IJ/f4OVpVWsw3ucrS28qn0/t/fHk4cEKI=; b=X+py0a72r73bLk0wFBnpN3Cd9kUeC1VjC9uRCOXzWwZEq8eV2aSUxBkrYF2S/7VAIa Hq5IEF9h/WG1aNDxTyjLSqgGyYFOktgLn3F4AWZFrhKKl0gQwuDl7uhJdiT2pdfntwZm twsuBRU+JG2pEbahEGzp1P2OXbVoKMHTVCKcKXeAo4CtZMlK4USySsocRTJdX30dvkqV X2EjuthS6qMZ1N/dmL3xobBq2yHSxe1s8mCMpJ6cWDQqbHvLN2e/ux60QSyauXQ/lS57 dgxHhA/9XWtu5pbqD6afbGCgP7VvIFpmzI24zAii944ExusyTQQnj/5GiGcLBzoa9pb4 tIog== X-Gm-Message-State: AGi0Pub3UzTf+QeEtzOxZvdEuuYLcIE230L2ZSEwBk3gXvs7w6OP7cYW C6ZymaWUw632wY2yqLggjHU= X-Google-Smtp-Source: APiQypJfyklPMFQQYQL1OuANyjySeCQPdGYH7TjSCjrF2emF6AGXFPjeHCraQdzzIrRauzMdS8QFpQ== X-Received: by 2002:a9d:d06:: with SMTP id 6mr25675586oti.188.1588112086606; Tue, 28 Apr 2020 15:14:46 -0700 (PDT) Received: from localhost.localdomain ([2604:1380:4111:8b00::1]) by smtp.gmail.com with ESMTPSA id 186sm5267476ooi.30.2020.04.28.15.14.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 Apr 2020 15:14:45 -0700 (PDT) From: Nathan Chancellor To: Thomas Bogendoerfer , Masahiro Yamada Cc: linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com, linux-kbuild@vger.kernel.org, Nick Desaulniers , Fangrui Song , Sami Tolvanen , Dmitry Golovin , Sedat Dilek , Nathan Chancellor Subject: [PATCH v4 4/5] MIPS: VDSO: Use $(LD) instead of $(CC) to link VDSO Date: Tue, 28 Apr 2020 15:14:18 -0700 Message-Id: <20200428221419.2530697-5-natechancellor@gmail.com> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200428221419.2530697-1-natechancellor@gmail.com> References: <20200423171807.29713-1-natechancellor@gmail.com> <20200428221419.2530697-1-natechancellor@gmail.com> MIME-Version: 1.0 X-Patchwork-Bot: notify Sender: linux-kbuild-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kbuild@vger.kernel.org Currently, the VDSO is being linked through $(CC). This does not match how the rest of the kernel links objects, which is through the $(LD) variable. When clang is built in a default configuration, it first attempts to use the target triple's default linker then the system's default linker, unless told otherwise through -fuse-ld=... We do not use -fuse-ld= because it can be brittle and we have support for invoking $(LD) directly. See commit fe00e50b2db8c ("ARM: 8858/1: vdso: use $(LD) instead of $(CC) to link VDSO") and commit 691efbedc60d2 ("arm64: vdso: use $(LD) instead of $(CC) to link VDSO") for examples of doing this in the VDSO. Do the same thing here. Replace the custom linking logic with $(cmd_ld) and ldflags-y so that $(LD) is respected. We need to explicitly add two flags to the linker that were implicitly passed by the compiler: -G 0 (which comes from ccflags-vdso) and --eh-frame-hdr. Before this patch (generated by adding '-v' to VDSO_LDFLAGS): /libexec/gcc/mips64-linux/9.3.0/collect2 \ -plugin /libexec/gcc/mips64-linux/9.3.0/liblto_plugin.so \ -plugin-opt=/libexec/gcc/mips64-linux/9.3.0/lto-wrapper \ -plugin-opt=-fresolution=/tmp/ccGEi5Ka.res \ --eh-frame-hdr \ -G 0 \ -EB \ -mips64r2 \ -shared \ -melf64btsmip \ -o arch/mips/vdso/vdso.so.dbg.raw \ -L/lib/gcc/mips64-linux/9.3.0/64 \ -L/lib/gcc/mips64-linux/9.3.0 \ -L/lib/gcc/mips64-linux/9.3.0/../../../../mips64-linux/lib \ -Bsymbolic \ --no-undefined \ -soname=linux-vdso.so.1 \ -EB \ --hash-style=sysv \ --build-id \ -T arch/mips/vdso/vdso.lds \ arch/mips/vdso/elf.o \ arch/mips/vdso/vgettimeofday.o \ arch/mips/vdso/sigreturn.o After this patch: /bin/mips64-linux-ld \ -m elf64btsmip \ -Bsymbolic \ --no-undefined \ -soname=linux-vdso.so.1 \ -EB \ -nostdlib \ -shared \ -G 0 \ --eh-frame-hdr \ --hash-style=sysv \ --build-id \ -T arch/mips/vdso/vdso.lds \ arch/mips/vdso/elf.o \ arch/mips/vdso/vgettimeofday.o arch/mips/vdso/sigreturn.o \ -o arch/mips/vdso/vdso.so.dbg.raw Note that we leave behind -mips64r2. Turns out that ld ignores it (see get_emulation in ld/ldmain.c). This is true of current trunk and 2.23, which is the minimum supported version for the kernel: https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=ld/ldmain.c;hb=aa4209e7b679afd74a3860ce25659e71cc4847d5#l593 https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=ld/ldmain.c;hb=a55e30b51bc6227d8d41f707654d0a5620978dcf#l641 Before this patch, LD=ld.lld did nothing: $ llvm-readelf -p.comment arch/mips/vdso/vdso.so.dbg | sed 's/(.*//' String dump of section '.comment': [ 0] ClangBuiltLinux clang version 11.0.0 After this patch, it does: $ llvm-readelf -p.comment arch/mips/vdso/vdso.so.dbg | sed 's/(.*//' String dump of section '.comment': [ 0] Linker: LLD 11.0.0 [ 62] ClangBuiltLinux clang version 11.0.0 Link: https://github.com/ClangBuiltLinux/linux/issues/785 Signed-off-by: Nathan Chancellor --- v3 -> v4: * Improve commit message to show that ld command is effectively the same as the one generated by GCC. * Add '-G 0' and '--eh-frame-hdr' because they were added by GCC. v2 -> v3: * New patch. arch/mips/vdso/Makefile | 13 ++++--------- 1 file changed, 4 insertions(+), 9 deletions(-) diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile index 92b53d1df42c3..2e64c7600eead 100644 --- a/arch/mips/vdso/Makefile +++ b/arch/mips/vdso/Makefile @@ -60,10 +60,9 @@ ifdef CONFIG_MIPS_DISABLE_VDSO endif # VDSO linker flags. -VDSO_LDFLAGS := \ - -Wl,-Bsymbolic -Wl,--no-undefined -Wl,-soname=linux-vdso.so.1 \ - $(addprefix -Wl$(comma),$(filter -E%,$(KBUILD_CFLAGS))) \ - -nostdlib -shared -Wl,--hash-style=sysv -Wl,--build-id +ldflags-y := -Bsymbolic --no-undefined -soname=linux-vdso.so.1 \ + $(filter -E%,$(KBUILD_CFLAGS)) -nostdlib -shared \ + -G 0 --eh-frame-hdr --hash-style=sysv --build-id -T CFLAGS_REMOVE_vdso.o = -pg @@ -82,11 +81,7 @@ quiet_cmd_vdso_mips_check = VDSOCHK $@ # quiet_cmd_vdsold_and_vdso_check = LD $@ - cmd_vdsold_and_vdso_check = $(cmd_vdsold); $(cmd_vdso_check); $(cmd_vdso_mips_check) - -quiet_cmd_vdsold = VDSO $@ - cmd_vdsold = $(CC) $(c_flags) $(VDSO_LDFLAGS) \ - -Wl,-T $(filter %.lds,$^) $(filter %.o,$^) -o $@ + cmd_vdsold_and_vdso_check = $(cmd_ld); $(cmd_vdso_check); $(cmd_vdso_mips_check) quiet_cmd_vdsoas_o_S = AS $@ cmd_vdsoas_o_S = $(CC) $(a_flags) -c -o $@ $<