[PATCH 7/7] Kbuild: lto: pass -m32/-m64 to to LDFINAL

Arnd Bergmann
2018-02-02T16:21:48Z

Building randconfig kernels with a biarch compiler fails with LTO
when the final link uses a different target architecture compared
to the earlier compilation stages.

Setting -m32 or -m64 in ${LDFINAL} solves this problem, though my
feeling is that there is a better way to do this. There might also
be other from KBUILD_CFLAGS that we may need in LDFINAL.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
Makefile | 2 +-
arch/x86/Makefile | 2 ++
scripts/Makefile.lto | 2 +-
3 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index 3b214c5a51a5..1a82fa39f82b 100644
--- a/Makefile
+++ b/Makefile
@@ -440,7 +440,7 @@ export CFLAGS_KASAN CFLAGS_KASAN_NOSANITIZE CFLAGS_UBSAN
export KBUILD_AFLAGS AFLAGS_KERNEL AFLAGS_MODULE
export KBUILD_AFLAGS_MODULE KBUILD_CFLAGS_MODULE KBUILD_LDFLAGS_MODULE
export KBUILD_AFLAGS_KERNEL KBUILD_CFLAGS_KERNEL
-export KBUILD_ARFLAGS
+export KBUILD_ARFLAGS KBUILD_BIARCHFLAGS

# When compiling out-of-tree modules, put MODVERDIR in the module
# tree rather than in the kernel tree. The kernel tree might
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index e79f0fda9aea..12425aafc7fc 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -69,6 +69,7 @@ ifeq ($(CONFIG_X86_32),y)
biarch := $(call cc-option,-m32)
KBUILD_AFLAGS += $(biarch)
KBUILD_CFLAGS += $(biarch)
+ KBUILD_BIARCHFLAGS += $(biarch)

KBUILD_CFLAGS += -msoft-float -mregparm=3 -freg-struct-return

@@ -97,6 +98,7 @@ else
biarch := -m64
KBUILD_AFLAGS += -m64
KBUILD_CFLAGS += -m64
+ KBUILD_BIARCHFLAGS += $(biarch)

# Align jump targets to 1 byte, not the default 16 bytes:
KBUILD_CFLAGS += $(call cc-option,-falign-jumps=1)
diff --git a/scripts/Makefile.lto b/scripts/Makefile.lto
index 2d6995ba7d0b..e57d025b7728 100644
--- a/scripts/Makefile.lto
+++ b/scripts/Makefile.lto
@@ -72,7 +72,7 @@ endif
KBUILD_CFLAGS += ${LTO_CFLAGS}

LDFINAL := ${CONFIG_SHELL} ${srctree}/scripts/gcc-ld \
- ${LTO_FINAL_CFLAGS}
+ ${LTO_FINAL_CFLAGS} ${KBUILD_BIARCHFLAGS}

# LTO gcc creates a lot of files in TMPDIR, and with /tmp as tmpfs
# it's easy to drive the machine OOM. Use the object directory
--
2.9.0