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Date:   Sun, 13 Mar 2022 09:52:14 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc:     Kumar Kartikeya Dwivedi <memxor@gmail.com>,
        X86 ML <x86@kernel.org>, joao@overdrivepizza.com,
        hjl.tools@gmail.com, Josh Poimboeuf <jpoimboe@redhat.com>,
        Andrew Cooper <andrew.cooper3@citrix.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Kees Cook <keescook@chromium.org>,
        Sami Tolvanen <samitolvanen@google.com>,
        Mark Rutland <mark.rutland@arm.com>, alyssa.milburn@intel.com,
        Miroslav Benes <mbenes@suse.cz>,
        Steven Rostedt <rostedt@goodmis.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>, bpf <bpf@vger.kernel.org>
Subject: Re: [PATCH v4 00/45] x86: Kernel IBT
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On Sat, Mar 12, 2022 at 05:33:39PM -0800, Alexei Starovoitov wrote:
> During the build with gcc 8.5 I see:
> 
> arch/x86/crypto/crc32c-intel.o: warning: objtool: file already has
> .ibt_endbr_seal, skipping
> arch/x86/crypto/crc32c-intel.o: warning: objtool: file already has
> .orc_unwind section, skipping
>   LD [M]  crypto/async_tx/async_xor.ko
>   LD [M]  crypto/authenc.ko
> make[3]: *** [../scripts/Makefile.modfinal:61:
> arch/x86/crypto/crc32c-intel.ko] Error 255
> make[3]: *** Waiting for unfinished jobs....
> 
> but make clean cures it.
> I suspect it's some missing makefile dependency.

Yes, I recently ran into it; I've been trying to kick Makefile into
submission but have not had success yet. Will try again on Monday.

Problem appears to be that it will re-link .ko even though .o hasn't
changed, resulting in duplicate objtool runs. I've been trying to have
makefile generate .o.objtool empty file to serve as dependency marker to
avoid doing second objtool run, but like said, no luck yet.

> and:
> vmlinux.o: warning: objtool: ksys_unshare()+0x626: unreachable instruction
> which stays even after make clean.

Humm, I shall have to dig out gcc-8.5 then.

> The rcu "false positive" is still there that causes
> sporadic hangs during the boot.

I've merged fix for that yesterday, shall respin this ibt tree to
include that.

> The test_progs shows:
> Summary: 228/1122 PASSED, 4 SKIPPED, 6 FAILED
> (when I remove one test)
> 
> That test is actually crashing the kernel:
> ./test_progs -t mod_race

Argh, I wasn't seeing crashing, I'll prod with sharp stick.