linux-kernel - Re: mm/kmsan/instrumentation.c:41:26: warning: no previous prototype for function '__msan_metadata_ptr_for_load

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Message-ID: <CAG_fn=Vz47zvCDoUENX5kH7Giena+w=yifWbMo28ayAUKU7kyQ@mail.gmail.com>
Date:   Thu, 12 Jan 2023 10:15:45 +0100
From:   Alexander Potapenko <glider@...gle.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     kernel test robot <lkp@...el.com>, llvm@...ts.linux.dev,
        oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Christoph Lameter <cl@...ux-foundation.org>,
        Marco Elver <elver@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>
Subject: Re: mm/kmsan/instrumentation.c:41:26: warning: no previous prototype
 for function '__msan_metadata_ptr_for_load_n'

> > Would it also make sense to exclude KMSAN with CONFIG_SLUB_TINY?
>
> If the root causes are fixed, then it's not necessary? AFAIK SLUB_TINY only
> indirectly caused KMSAN to be newly enabled in some configs, but there's no
> fundamental incompatibility that I know of.

So far I couldn't manage to boot KMSAN with SLUB_TINY, it just dies
somewhere very early with the following stacktrace:

#0  0xffffffff9044134a in native_halt () at ./arch/x86/include/asm/irqflags.h:57
#1  halt () at ./arch/x86/include/asm/irqflags.h:98
#2  early_fixup_exception (regs=regs@...ry=0xffffffff8fa03d08,
trapnr=trapnr@...ry=14) at arch/x86/mm/extable.c:340
#3  0xffffffff903c23db in do_early_exception (regs=0xffffffff8fa03d08,
trapnr=14) at arch/x86/kernel/head64.c:424
#4  0xffffffff903c214f in early_idt_handler_common () at
arch/x86/kernel/head_64.S:483
#5  0x0000000000000000 in ?? ()

The same kernel boots (to some extent) without CONFIG_KMSAN, so my
guess is that we're instrumenting something that is not supposed to be
instrumented.
But SLUB_TINY doesn't add new source files, and it's also unlikely to
kick in before mm_init(), right?

-- 
Alexander Potapenko
Software Engineer

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