LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Matthias Kaehlcke <mka@chromium.org>
To: Russell King - ARM Linux <linux@armlinux.org.uk>
Cc: Stefan Agner <stefan@agner.ch>,
	ard.biesheuvel@linaro.org, arnd@arndb.de,
	nicolas.pitre@linaro.org, marc.zyngier@arm.com,
	behanw@converseincode.com, keescook@chromium.org,
	Bernhard.Rosenkranzer@linaro.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 5/5] ARM: add support for building ARM kernel with clang
Date: Tue, 20 Mar 2018 17:20:22 -0700	[thread overview]
Message-ID: <20180321002022.GH37438@google.com> (raw)
In-Reply-To: <20180320231832.GK2743@n2100.armlinux.org.uk>

El Tue, Mar 20, 2018 at 11:18:33PM +0000 Russell King - ARM Linux ha dit:

> On Wed, Mar 21, 2018 at 12:02:06AM +0100, Stefan Agner wrote:
> > Use cc-options call for compiler options which are not available
> > in clang. With this patch an ARMv7 multi platform kernel can be
> > successfully build using clang (tested with version 5.0.1).
> > 
> > Based-on-patches-by: Behan Webster <behanw@converseincode.com>
> > Signed-off-by: Stefan Agner <stefan@agner.ch>

Great to see your work on bringing clang support for 32-bit ARM
upstream!

> > ---
> >  arch/arm/Makefile                 | 2 +-
> >  arch/arm/boot/compressed/Makefile | 2 +-
> >  2 files changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/arm/Makefile b/arch/arm/Makefile
> > index e9e3fde3c657..20e9fee1ccc5 100644
> > --- a/arch/arm/Makefile
> > +++ b/arch/arm/Makefile
> > @@ -39,7 +39,7 @@ KBUILD_CFLAGS	+= $(call cc-option,-mno-unaligned-access)
> >  endif
> >  
> >  ifeq ($(CONFIG_FRAME_POINTER),y)
> > -KBUILD_CFLAGS	+=-fno-omit-frame-pointer -mapcs -mno-sched-prolog
> > +KBUILD_CFLAGS	+=-fno-omit-frame-pointer $(call cc-option,-mapcs,) $(call cc-option,-mno-sched-prolog,)
> 
> Some of these options here are to ensure that we generate the following
> code, so we can backtrace:
> 
> 	mov	ip, sp
> 	stmfd	sp!, {fp, ip, lr, pc}
> 	sub	fp, ip, #4
> 
> If clang isn't producing that code at the start of functions with
> CONFIG_FRAME_POINTER=y, then backtracing will not work, and arguably
> CONFIG_FRAME_POINTER=y is useless there.  In that circumstance, it's
> probably better to fail so the user can configure something more
> debuggable, rather than having the kernel potentially producing
> undebuggable oopses.

Which option in particular is important to generate the above code for
backstracing?

According to the gcc doc -mapcs(-frame) is deprecated.

For -mno-sched-prolog the doc says:

"Prevent the reordering of instructions in the function prologue, or
the merging of those instruction with the instructions in the
function’s body. This means that all functions start with a
recognizable set of instructions (or in fact one of a choice from a
small set of different function prologues), and this information can
be used to locate the start of functions inside an executable piece of
code. The default is -msched-prolog."

Thanks

Matthias

  reply	other threads:[~2018-03-21  0:20 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-20 23:02 [PATCH 0/5] ARM: clang support Stefan Agner
2018-03-20 23:02 ` [PATCH 1/5] bus: arm-cci: use asm unreachable Stefan Agner
2018-03-20 23:30   ` Russell King - ARM Linux
2018-03-21  8:22     ` Stefan Agner
2018-03-20 23:02 ` [PATCH 2/5] efi/libstub/arm: add support for building with clang Stefan Agner
2018-03-20 23:02 ` [PATCH 3/5] ARM: trusted_foundations: do not use naked function Stefan Agner
2018-03-20 23:13   ` Russell King - ARM Linux
2018-03-21  8:41     ` Stefan Agner
2018-03-21 12:13   ` Robin Murphy
2018-03-21 14:09     ` Stefan Agner
2018-03-21 15:26       ` Dmitry Osipenko
2018-03-21 16:40         ` Stephen Warren
2018-03-21 17:16           ` Robin Murphy
2018-03-21 21:41             ` Stefan Agner
2018-03-22 11:48               ` Robin Murphy
2018-03-22 12:43                 ` Stefan Agner
2018-03-22 14:03                   ` Dmitry Osipenko
2018-03-20 23:02 ` [PATCH 4/5] ARM: drop no-thumb-interwork in EABI mode Stefan Agner
2018-03-20 23:02 ` [PATCH 5/5] ARM: add support for building ARM kernel with clang Stefan Agner
2018-03-20 23:18   ` Russell King - ARM Linux
2018-03-21  0:20     ` Matthias Kaehlcke [this message]
2018-03-21  9:03       ` Stefan Agner
2018-03-25 13:24     ` Stefan Agner

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20180321002022.GH37438@google.com \
    --to=mka@chromium.org \
    --cc=Bernhard.Rosenkranzer@linaro.org \
    --cc=ard.biesheuvel@linaro.org \
    --cc=arnd@arndb.de \
    --cc=behanw@converseincode.com \
    --cc=keescook@chromium.org \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux@armlinux.org.uk \
    --cc=marc.zyngier@arm.com \
    --cc=nicolas.pitre@linaro.org \
    --cc=stefan@agner.ch \
    --subject='Re: [PATCH 5/5] ARM: add support for building ARM kernel with clang' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).