From: Thomas Gleixner <tglx@linutronix.de>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: mingo@redhat.com, bp@alien8.de, peterz@infradead.org,
clang-built-linux@googlegroups.com, linux-kernel@vger.kernel.org,
yamada.masahiro@socionext.com,
Vaibhav Rustagi <vaibhavrustagi@google.com>,
"H. Peter Anvin" <hpa@zytor.com>,
x86@kernel.org
Subject: Re: [PATCH v4 2/2] x86/purgatory: use CFLAGS_REMOVE rather than reset KBUILD_CFLAGS
Date: Wed, 7 Aug 2019 15:17:21 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.2.21.1908071517120.24014@nanos.tec.linutronix.de> (raw)
In-Reply-To: <alpine.DEB.2.21.1907261012140.1791@nanos.tec.linutronix.de>
On Fri, 26 Jul 2019, Thomas Gleixner wrote:
Ping...
> On Thu, 25 Jul 2019, Nick Desaulniers wrote:
>
> > KBUILD_CFLAGS is very carefully built up in the top level Makefile,
> > particularly when cross compiling or using different build tools.
> > Resetting KBUILD_CFLAGS via := assignment is an antipattern.
> >
> > The comment above the reset mentions that -pg is problematic. Other
> > Makefiles use `CFLAGS_REMOVE_file.o = $(CC_FLAGS_FTRACE)` when
> > CONFIG_FUNCTION_TRACER is set. Prefer that pattern to wiping out all of
> > the important KBUILD_CFLAGS then manually having to re-add them. Seems
> > also that __stack_chk_fail references are generated when using
> > CONFIG_STACKPROTECTOR or CONFIG_STACKPROTECTOR_STRONG.
>
> Looking at the resulting build flags. Most stuff looks correct but there
> are a few which need to be looked at twice.
>
> removes:
>
> -ffreestanding
> -fno-builtin
> -fno-zero-initialized-in-bss
>
> changes:
>
> -mcmodel=large to -mcmodel=kernel
>
> adds:
>
> -mindirect-branch-register
> -mindirect-branch=thunk-extern
>
> The latter makes me nervous. That probably wants to have retpoline disabled
> as well. It's not having an instance right now, but ...
>
> Thanks,
>
> tglx
>
next prev parent reply other threads:[~2019-08-07 13:17 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-25 20:06 [PATCH v4 1/2] x86/purgatory: do not use __builtin_memcpy and __builtin_memset Nick Desaulniers
2019-07-25 20:06 ` [PATCH v4 2/2] x86/purgatory: use CFLAGS_REMOVE rather than reset KBUILD_CFLAGS Nick Desaulniers
2019-07-26 8:54 ` Thomas Gleixner
2019-08-07 13:17 ` Thomas Gleixner [this message]
2019-07-25 20:06 ` [PATCH v4 0/2] Support kexec/kdump for clang built kernel Nick Desaulniers
2019-07-25 22:51 ` Thomas Gleixner
2019-07-25 22:57 ` Nick Desaulniers
2019-07-25 23:09 ` Thomas Gleixner
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