linux-kernel - Re: linux-next: Tree for May 14 (objtool 2/2)

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Date:   Fri, 29 May 2020 12:54:56 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Randy Dunlap <rdunlap@...radead.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Linux Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: linux-next: Tree for May 14 (objtool 2/2)

On Thu, May 28, 2020 at 11:06:32PM -0700, Kees Cook wrote:
> On Thu, May 28, 2020 at 10:44:04AM -0500, Josh Poimboeuf wrote:
> > On Thu, May 14, 2020 at 09:04:36AM -0700, Randy Dunlap wrote:
> > > On 5/14/20 4:07 AM, Stephen Rothwell wrote:
> > > > Hi all,
> > > > 
> > > > Changes since 20200512:
> > > > 
> > > 
> > > on x86_64:
> > > 
> > > drivers/ide/ide-tape.o: warning: objtool: ide_tape_discard_merge_buffer.constprop.7()+0x4e: unreachable instruction
> > > drivers/scsi/sd.o: warning: objtool: sd_pr_clear()+0x1e: unreachable instruction
> > > drivers/scsi/sd_zbc.o: warning: objtool: sd_zbc_update_wp_offset_workfn()+0xec: unreachable instruction
> > > drivers/target/target_core_xcopy.o: warning: objtool: target_xcopy_do_work()+0xdd6: unreachable instruction
> > > 
> > > 
> > > randconfig file is attached.
> > 
> > Kees,
> > 
> > More UBSAN_TRAP fun.  This randconfig has:
> > 
> > CONFIG_UBSAN_TRAP=y
> > CONFIG_UBSAN_ALIGNMENT=y
> > # CONFIG_COMPILE_TEST is not set
> 
> Ugh, I thought CONFIG_COMPILE_TEST always gets set for randconfig and
> the all*config choices, but now I see that CONFIG_COMPILE_TEST is
> enabled due to the "all" part of the all*config choices. Okay. Big
> hammer:

Yeah, I didn't realize that either... /me wonders if that should change.

> diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan
> index 929211039bac..27bcc2568c95 100644
> --- a/lib/Kconfig.ubsan
> +++ b/lib/Kconfig.ubsan
> @@ -63,7 +63,7 @@ config UBSAN_SANITIZE_ALL
>  config UBSAN_ALIGNMENT
>         bool "Enable checks for pointers alignment"
>         default !HAVE_EFFICIENT_UNALIGNED_ACCESS
> -       depends on !X86 || !COMPILE_TEST
> +       depends on !UBSAN_TRAP
>         help
>           This option enables the check of unaligned memory accesses.
>           Enabling this option on architectures that support unaligned
> 
> How about that?

But I thought you said the alignment traps might be useful on other
arches?  Should it be

	depends on !X86 || !UBSAN_TRAP

?

-- 
Josh