linux-kernel - [PATCH] Makefile: add -fuse-ld=lld to KBUILD

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Message-Id: <20200820220955.3325555-1-ndesaulniers@google.com>
Date:   Thu, 20 Aug 2020 15:09:55 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>, stable@...r.kernel.org,
        Matthias Maennich <maennich@...gle.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com
Subject: [PATCH] Makefile: add -fuse-ld=lld to KBUILD_HOSTLDFLAGS when LLVM=1

While moving Android kernels over to use LLVM=1, we observe the failure
when building in a hermetic docker image:
  HOSTCC  scripts/basic/fixdep
clang: error: unable to execute command: Executable "ld" doesn't exist!

The is because the build of the host utility fixdep builds the fixdep
executable in one step by invoking the compiler as the driver, rather
than individual compile then link steps.

Clang when configured from source defaults to use the system's linker,
and not LLVM's own LLD, unless the CMake config
-DCLANG_DEFAULT_LINKER='lld' is set when configuring a build of clang
itself.

Don't rely on the compiler's implicit default linker; be explicit.

Cc: stable@...r.kernel.org
Fixes: commit a0d1c951ef08 ("kbuild: support LLVM=1 to switch the default tools to Clang/LLVM")
Reported-by: Matthias Maennich <maennich@...gle.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
 Makefile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/Makefile b/Makefile
index def590b743a9..b4e93b228a26 100644
--- a/Makefile
+++ b/Makefile
@@ -436,6 +436,7 @@ OBJDUMP		= llvm-objdump
 READELF		= llvm-readelf
 OBJSIZE		= llvm-size
 STRIP		= llvm-strip
+KBUILD_HOSTLDFLAGS	+= -fuse-ld=lld
 else
 CC		= $(CROSS_COMPILE)gcc
 LD		= $(CROSS_COMPILE)ld
-- 
2.28.0.297.g1956fa8f8d-goog