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SubjectRe: x86/purgatory: undefined symbol __stack_chk_fail
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On 03/09/2019 17.50, Andreas Smas wrote:
> Hi,
>
> For me, kernels built including this commit
> b059f801a937 (x86/purgatory: Use CFLAGS_REMOVE rather than reset KBUILD_CFLAGS)
>
> results in kexec() failing to load the kernel:
>
> kexec: Undefined symbol: __stack_chk_fail
> kexec-bzImage64: Loading purgatory failed
>
> Can be seen:
>
> $ readelf -a arch/x86/purgatory/purgatory.ro | grep UND
> 0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
> 51: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND __stack_chk_fail
>
> Using: gcc version 7.4.0 (Ubuntu 7.4.0-1ubuntu1~18.04.1)

Ubuntu's gcc has -fstack-protector enabled by default, so this happens
if one doesn't pass -fno-stack-protector (which I guess is implied by
-ffreestanding) explicitly.

> Adding -ffreestanding or -fno-stack-protector to ccflags-y in
> arch/x86/purgatory/Makefile
> fixes the problem. Not sure which would be preferred.

Probably -fno-stack-protector, guarded by
CONFIG_CC_HAS_STACKPROTECTOR_NONE (because not all gccs understand
-fno-stack-protector), so

ifdef CONFIG_CC_HAS_STACKPROTECTOR_NONE
ccflags-y += -fno-stack-protector
endif

Rasmus

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