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Subject[PATCH] ARM: change link order of $(mmy-y) to avoid veneers
Date
The kernel compiled with multi_v7_defconfig + CONFIG_KASAN=y +
CONFIG_KASAN_INLINE=y does not boot.

I do not think KASAN is the direct reason of the boot failure.
CONFIG_KASAN_INLINE is just one example configuration that grows the
image size significantly and makes a big distance between function
callers and callees.

I see some veneers for __get_user_* in the bad kernel image. I am
not perfectly clear, but __get_user_* may not work with veneers for
some reasons.

If I move the link order of arch/arm/lib/getuser.S, the veneers are
gone, and the kernel gets working again.

I do not see a good reason that $(mmu-y) must be added to lib-y because
all the code in $(mmu-y) is mandatory. Add it to obj-y to move the code
to lower address.

[1] multi_v7_defconfig (works)

$ arm-linux-gnueabihf-nm vmlinux | grep __get_user_1
c072a450 T __get_user_1
c17ea033 r __kstrtab___get_user_1
c18119fe r __kstrtabns___get_user_1
c17c4878 r __ksymtab___get_user_1

[2] multi_v7_defconfig + CONFIG_KASAN_INLINE (does not work)

$ arm-linux-gnueabihf-nm vmlinux | grep __get_user_1
c341ec2c T __get_user_1
c06e3580 t ____get_user_1_veneer
c0adc6c0 t ____get_user_1_veneer
c12cf054 t ____get_user_1_veneer
c43f42cc r __kstrtab___get_user_1
c441c128 r __kstrtabns___get_user_1
c43cead8 r __ksymtab___get_user_1

[3] multi_v7_defconfig + CONFIG_KASAN_INLINE + this patch (works)

$ arm-linux-gnueabihf-nm vmlinux | grep __get_user_1
c10975b0 T __get_user_1
c43f42cc r __kstrtab___get_user_1
c441c128 r __kstrtabns___get_user_1
c43cead8 r __ksymtab___get_user_1

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---

arch/arm/lib/Makefile | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile
index 650404be6768..4d092ef87a1d 100644
--- a/arch/arm/lib/Makefile
+++ b/arch/arm/lib/Makefile
@@ -28,7 +28,7 @@ endif
# using lib_ here won't override already available weak symbols
obj-$(CONFIG_UACCESS_WITH_MEMCPY) += uaccess_with_memcpy.o

-lib-$(CONFIG_MMU) += $(mmu-y)
+obj-$(CONFIG_MMU) += $(mmu-y)

ifeq ($(CONFIG_CPU_32v3),y)
lib-y += io-readsw-armv3.o io-writesw-armv3.o
--
2.39.2
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