linux-kernel - Re: Remaining randconfig objtool warnings, linux-next-20200428

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Date:   Tue, 28 Apr 2020 11:10:44 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: Remaining randconfig objtool warnings, linux-next-20200428

On Tue, Apr 28, 2020 at 04:49:15PM +0200, Arnd Bergmann wrote:
> I noticed the number of objtool warnings in randconfig kernels have gone down
>  recently, maybe it's possible to eliminate the remaining ones?
> 
> Here are the ones I ran into recently, using gcc-9.3:
> 
> ==> build/x86/0x3D2B5D6D_defconfig/log <==
> arch/x86/kvm/vmx/vmx.o: warning: objtool: vmx_handle_exit_irqoff()+0x24: unreachable instruction

This is a legit warning caused by CONFIG_UBSAN_TRAP +
CONFIG_UBSAN_ALIGNMENT, I think Kees is going to do a fix.

> ==> build/x86/0xFD7B7323_defconfig/log <==
> arch/x86/entry/entry_64.o: warning: objtool: .entry.text+0x991: unreachable instruction

This warning looks correct, did you make a change to entry_64.S?

> ==> build/x86/0x7942F24A_defconfig/log <==
> samples/ftrace/ftrace-direct.o: warning: objtool: .text+0x0: unreachable instruction
> samples/ftrace/ftrace-direct-too.o: warning: objtool: .text+0x0: unreachable instruction
> samples/ftrace/ftrace-direct-modify.o: warning: objtool: .text+0x0: unreachable instruction

I posted a fix for these a few days ago:

https://lkml.kernel.org/r/86c1cbca67cb353da9f335643ef5fd19bd82988f.1587761369.git.jpoimboe@redhat.com

> ==> build/x86/0xE0F2ACFF_defconfig/log <==
> kernel/time/posix-stubs.o: warning: objtool: __x64_sys_timer_create()+0x23: sibling call from callable instruction with modified stack frame
>
> ==> build/x86/0x2EA4CE4F_defconfig/log <==
> kernel/kcov.o: warning: objtool: write_comp_data()+0x1b: call to check_kcov_mode() with UACCESS enabled
> kernel/kcov.o: warning: objtool: __sanitizer_cov_trace_pc()+0x15: call to check_kcov_mode() with UACCESS enabled
> 
> ==> build/x86/0x500B1B82_defconfig/log <==
> kernel/bpf/core.o: warning: objtool: ___bpf_prog_run()+0x1269: call
> without frame pointer save/setup

I'll look into these.

-- 
Josh