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I have a yocto image for an ARM target. I am building kernel modules on the ARM target and have found an odd problem. Can anyone suggest a solution?

On the target I have run "make scripts prepare modules_prepare". I have an out of tree module and it builds correctly and modules_install inserts the module into the extra folder adding the name of the module to the end of modules.dep. So this tells me that my environment is correct.

I have an in tree module that I included as a module in the kernel config. The module Makefile is identical (apart from the name) for my in tree module however when I type make I get a lot of messages similar to

/tmp/ccz5G4aS.s: Assembler messages:
/tmp/ccz5G4aS.s:1400: Error: selected processor does not support `dsb ' in ARM mode

Using make -pq I have looked at the KBUILD_AFLAGS / KBUILD_CFLAGS and they seem to be the same for the two modules but still the in tree module build fails.

Something must be different but I can't work out how to debug and fix the different between the two module builds. I have a work around idea to try to build the in tree module with a different name but it would be good to fix this properly.

KBUILD_CFLAGS := -Wall -Wundef -Werror=strict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -fshort-wchar -fno-PIE -Werror=implicit-function-declaration -Werror=implicit-int -Werror=return-type -Wno-format-security -std=gnu89 -fno-dwarf2-cfi-asm -fno-ipa-sra -mabi=aapcs-linux -mfpu=vfp -funwind-tables -marm -Wa,-mno-warn-deprecated -D__LINUX_ARM_ARCH__=7 -march=armv5t -Wa,-march=armv7-a   -msoft-float -Uarm -fno-delete-null-pointer-checks -Wno-frame-address -Wno-format-truncation -Wno-format-overflow -Wno-address-of-packed-member -O2 -fno-allow-store-data-races -Wframe-larger-than=1024 -fstack-protector-strong -Wno-unused-but-set-variable -Wimplicit-fallthrough -Wno-unused-const-variable -fomit-frame-pointer -g -Wdeclaration-after-statement -Wvla -Wno-pointer-sign -Wno-stringop-truncation -Wno-zero-length-bounds -Wno-array-bounds -Wno-stringop-overflow -Wno-restrict -Wno-maybe-uninitialized -fno-strict-overflow -fno-stack-check -fconserve-stack -Werror=date-time -Werror=incompatible-pointer-types -Werror=designated-init -Wno-packed-not-aligned

KBUILD_AFLAGS := -D__ASSEMBLY__ -fno-PIE -mabi=aapcs-linux -mfpu=vfp -funwind-tables -marm -Wa,-mno-warn-deprecated -D__LINUX_ARM_ARCH__=7 -march=armv5t -Wa,-march=armv7-a  -include asm/unified.h -msoft-float -Wa,-gdwarf-2
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  • It could be an issue with the toolchain and perhaps tinkering with the build flags are not the best way to deal with it. Commented Jun 23 at 10:06

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I have just stumbled upon a better work round for this problem - https://lore.kernel.org/linux-arm-kernel/[email protected]/ - the arch/arm/Makefile can be modified to remove all the cc-option commands that modify the architecture specific and tuning specific compiler options!

I presume that the out of tree module build does not for some reason use the arch/arm/Makefile whilst my in-tree module build uses the Makefile an so has the build problem with gcc v11 and above.

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