linux-kernel - Re: [PATCH v5 00/29] Add support for Clang LTO

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Date:   Fri, 9 Oct 2020 19:38:38 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com,
        kernel-hardening@...ts.openwall.com, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        x86@...nel.org
Subject: Re: [PATCH v5 00/29] Add support for Clang LTO

On Fri, 9 Oct 2020 14:05:48 -0700
Sami Tolvanen <samitolvanen@...gle.com> wrote:

> Ah yes, X86_DECODER_SELFTEST seems to be broken in tip/master. If you
> prefer, I have these patches on top of mainline here:
> 
>   https://github.com/samitolvanen/linux/tree/clang-lto
> 
> Testing your config with LTO on this tree, it does build and boot for
> me, although I saw a couple of new objtool warnings, and with LLVM=1,
> one warning from llvm-objdump.

Thanks, I disabled X86_DECODER_SELFTEST and it now builds.

I forced the objdump mcount logic with the below patch, which produces:

CONFIG_FTRACE_MCOUNT_RECORD=y
CONFIG_FTRACE_MCOUNT_USE_OBJTOOL=y

But I don't see the __mcount_loc sections being created.

I applied patches 1 - 6.

-- Steve

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 89263210ab26..3042619e21b7 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -606,7 +606,7 @@ config FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY
 
 config FTRACE_MCOUNT_USE_CC
 	def_bool y
-	depends on $(cc-option,-mrecord-mcount)
+	depends on $(cc-option,-mrecord-mcount1)
 	depends on !FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY
 	depends on FTRACE_MCOUNT_RECORD