linux-kernel - Re: Linux 5.8-rc1

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Date:   Tue, 16 Jun 2020 16:33:52 -0400
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Gabriel C <nix.or.die@...glemail.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Hans de Goede <hdegoede@...hat.com>
Subject: Re: Linux 5.8-rc1

On Tue, Jun 16, 2020 at 10:11:46PM +0200, Gabriel C wrote:
> * Am So., 14. Juni 2020 um 22:44 Uhr schrieb Linus Torvalds
> <torvalds@...ux-foundation.org>:
> 
> Hello,
> 
> > So I didn't really expect this, but 5.8 looks to be one of our biggest
> > releases of all time.
> >
> 
> I hit a compiler error caused by e4160b2e4b02377c67f8ecd05786811598f39acd.
> 
> x86/purgatory: Fail the build if purgatory.ro has missing symbols
> 
> Having CONFIG_STACKPROTECTOR* & CONFIG_KEXEC_FILE enabled always
> results in a linking error like this:
> 
> LD      arch/x86/purgatory/purgatory.chk
> ld: arch/x86/purgatory/purgatory.ro: in function `verify_sha256_digest':
> purgatory.c:(.text+0x108): undefined reference to `__stack_chk_fail'
> ld: arch/x86/purgatory/purgatory.ro: in function `sha256_transform':
> sha256.c:(.text+0x1c74): undefined reference to `__stack_chk_fail'
> ld: arch/x86/purgatory/purgatory.ro: in function `__sha256_final':
> sha256.c:(.text+0x1e65): undefined reference to `__stack_chk_fail'
> ld: arch/x86/purgatory/purgatory.ro: in function `_kstrtoull':
> string.c:(.text+0x2107): undefined reference to `__stack_chk_fail'
> 
> I didn't look closer at that but from the error, it seems to be,
> some missing -fstack-protector* vs -fno-stack-protector* checks
> somewhere.
> 
> 
> Best Regards,
> 
> Gabriel C

Can you attach the output of gcc -dumpspecs and gcc -v? I suspect your
compiler enables stack protector by default. My distro compiler does
that too, but not if -ffreestanding is enabled (which it is for the
purgatory).

Does this patch help?

diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
index b04e6e72a592..088bd764e0b7 100644
--- a/arch/x86/purgatory/Makefile
+++ b/arch/x86/purgatory/Makefile
@@ -34,6 +34,7 @@ KCOV_INSTRUMENT := n
 PURGATORY_CFLAGS_REMOVE := -mcmodel=kernel
 PURGATORY_CFLAGS := -mcmodel=large -ffreestanding -fno-zero-initialized-in-bss
 PURGATORY_CFLAGS += $(DISABLE_STACKLEAK_PLUGIN) -DDISABLE_BRANCH_PROFILING
+PURGATORY_CFLAGS += $(call cc-option,-fno-stack-protector)
 
 # Default KBUILD_CFLAGS can have -pg option set when FTRACE is enabled. That
 # in turn leaves some undefined symbols like __fentry__ in purgatory and not