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

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Date:   Thu, 04 Jan 2018 19:25:12 +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 18:32:03 CET Josh Poimboeuf wrote:
> On Thu, Jan 04, 2018 at 05:56:30PM +0100, Markus wrote:
> > On Thursday, 4 January 2018 16:46:13 CET Josh Poimboeuf wrote:
> > > 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.
> 
> Ah, that explains it.  With CONFIG_MODVERSIONS, the linker does some
> work after gcc, but before objtool.  Can you try this patch?  (Note this
> isn't the final patch, as this breaks the CONFIG_MODVERSIONS=n case.)
> 
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index cb8997ed0149..3cf3cc6077ea 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -270,7 +270,7 @@ endif
>  # 'OBJECT_FILES_NON_STANDARD_foo.o := 'n': override directory skip for a
> file cmd_objtool = $(if $(patsubst y%,, \
>  	$(OBJECT_FILES_NON_STANDARD_$(basetarget).o)$
(OBJECT_FILES_NON_STANDARD)n)
> , \ -	$(__objtool_obj) $(objtool_args) "$(@)";)
> +	$(__objtool_obj) $(objtool_args) "$(@D)/.tmp_$(@F)";)
>  objtool_obj = $(if $(patsubst y%,, \
>  	$(OBJECT_FILES_NON_STANDARD_$(basetarget).o)$
(OBJECT_FILES_NON_STANDARD)n)
> , \ $(__objtool_obj))
> @@ -286,16 +286,16 @@ objtool_dep = $(objtool_obj)					\
>  define rule_cc_o_c
>  	$(call echo-cmd,checksrc) $(cmd_checksrc)			  \
>  	$(call cmd_and_fixdep,cc_o_c)					  \
> +	$(call echo-cmd,objtool) $(cmd_objtool)				  \
>  	$(cmd_modversions_c)						  \
>  	$(cmd_checkdoc)							  \
> -	$(call echo-cmd,objtool) $(cmd_objtool)				  \
>  	$(call echo-cmd,record_mcount) $(cmd_record_mcount)
>  endef
> 
>  define rule_as_o_S
>  	$(call cmd_and_fixdep,as_o_S)					  \
> -	$(cmd_modversions_S)						  \
> -	$(call echo-cmd,objtool) $(cmd_objtool)
> +	$(call echo-cmd,objtool) $(cmd_objtool)				  \
> +	$(cmd_modversions_S)
>  endef
> 
>  # List module undefined symbols (or empty line if not enabled)

With that patch the kernel is building with ld.gold.

BR,
Markus