linux-kernel - Re: objtool segfault with ORC unwinder enabled

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Date:   Thu, 4 Jan 2018 09:46:13 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Markus <M4rkusXXL@....de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: objtool segfault with ORC unwinder enabled

On Wed, Jan 03, 2018 at 06:26:19PM +0100, Markus wrote:
> > > > I'm unable to recreate.  Can you attach one of the .o files (like the
> > > > above irq.o)?
> > > 
> > > Sure, see attached. (From vanilla linux-4.14.11.)
> > 
> > There's something weird with the toolchain.  The object file doesn't
> > have an ELF section symbol for the .irqentry.text section.
> > 
> > Are there any special KCFLAGS being added?  Can you build the object
> > with V=1 to show the full gcc command line?
> 
> I have not added anything. There is no env variable set like $KCFLAGS or 
> $CFLAGS. (If that was the question.)
> 
> I think you mean this line from output:
> gcc -Wp,-MD,arch/x86/kernel/.irq.o.d  -nostdinc -isystem /usr/lib/gcc/x86_64-
> pc-linux-gnu/6.4.0/include -I./arch/x86/include -I./arch/x86/include/generated  
> -I./include -I./arch/x86/include/uapi -I./arch/x86/include/generated/uapi -I./
> include/uapi -I./include/generated/uapi -include ./include/linux/kconfig.h -
> D__KERNEL__ -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs -fno-strict-
> aliasing -fno-common -fshort-wchar -Werror-implicit-function-declaration -Wno-
> format-security -std=gnu89 -fno-PIE -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -
> mno-avx -m64 -falign-jumps=1 -falign-loops=1 -mno-80387 -mno-fp-ret-in-387 -
> mpreferred-stack-boundary=3 -mskip-rax-setup -mtune=generic -mno-red-zone -
> mcmodel=kernel -funit-at-a-time -DCONFIG_AS_CFI=1 -
> DCONFIG_AS_CFI_SIGNAL_FRAME=1 -DCONFIG_AS_CFI_SECTIONS=1 -DCONFIG_AS_FXSAVEQ=1 
> -DCONFIG_AS_SSSE3=1 -DCONFIG_AS_CRC32=1 -DCONFIG_AS_AVX=1 -DCONFIG_AS_AVX2=1 -
> DCONFIG_AS_AVX512=1 -DCONFIG_AS_SHA1_NI=1 -DCONFIG_AS_SHA256_NI=1 -pipe -Wno-
> sign-compare -fno-asynchronous-unwind-tables -fno-delete-null-pointer-checks -
> Wno-frame-address -O2 --param=allow-store-data-races=0 -DCC_HAVE_ASM_GOTO -
> Wframe-larger-than=2048 -fno-stack-protector -Wno-unused-but-set-variable -
> Wno-unused-const-variable -fomit-frame-pointer -fno-var-tracking-assignments -
> Wdeclaration-after-statement -Wno-pointer-sign -fno-strict-overflow -fno-
> stack-check -fconserve-stack -Werror=implicit-int -Werror=strict-prototypes -
> Werror=date-time -Werror=incompatible-pointer-types -Werror=designated-init -
> Iarch/x86/kernel/../include/asm/trace    -DKBUILD_BASENAME='"irq"'  -
> DKBUILD_MODNAME='"irq"' -c -o arch/x86/kernel/.tmp_irq.o arch/x86/kernel/irq.c
> 
> The next line is the objtool that segfaults.

I don't see anything unusual there.  Are there any Gentoo patches
against either the kernel or GCC which would strip unused symbols?

-- 
Josh