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

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Message-ID: <2752107.fJzmbfloTe@markus>
Date:   Thu, 04 Jan 2018 17:56:30 +0100
From:   Markus <M4rkusXXL@....de>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
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 Thursday, 4 January 2018 16:46:13 CET Josh Poimboeuf wrote:
> 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?

The kernel is the vanilla kernel. (4.14.11 and also 4.15-rc6)
Its not a gentoo specific gcc patch. (Then every gentoo user would be 
affected?)

But I enabled ld.gold as default linker like 5 years ago. Never had a problem 
with this.

Is ld.gold supposed to fail here?

I switched back to ld.bfd and it seems to work.

BR,
Markus