Re: [PATCH] kprobes: Enable tracing for mololithic kernel images

From: Luis Chamberlain <mcgrof@kernel.org>
To: "Russell King (Oracle)" <linux@armlinux.org.uk>,
	"Edgecombe, Rick P" <rick.p.edgecombe@intel.com>,
	Christoph Hellwig <hch@infradead.org>
Cc: "Jarkko Sakkinen" <jarkko@profian.com>,
	linux-kernel@vger.kernel.org,
	"Nathaniel McCallum" <nathaniel@profian.com>,
	"Jarkko Sakkinen" <jarkko@kernel.org>,
	"Catalin Marinas" <catalin.marinas@arm.com>,
	"Will Deacon" <will@kernel.org>,
	"Thomas Bogendoerfer" <tsbogend@alpha.franken.de>,
	"James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
	"Helge Deller" <deller@gmx.de>,
	"Michael Ellerman" <mpe@ellerman.id.au>,
	"Benjamin Herrenschmidt" <benh@kernel.crashing.org>,
	"Paul Mackerras" <paulus@samba.org>,
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Subject: Re: [PATCH] kprobes: Enable tracing for mololithic kernel images
Date: Thu, 9 Jun 2022 06:44:45 -0700	[thread overview]
Message-ID: <YqH5TfN9w35kHFLU@bombadil.infradead.org> (raw)
In-Reply-To: <YqGlmpbx8HTrWmpF@shell.armlinux.org.uk>

On Thu, Jun 09, 2022 at 08:47:38AM +0100, Russell King (Oracle) wrote:
> On Wed, Jun 08, 2022 at 02:59:27AM +0300, Jarkko Sakkinen wrote:
> > diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
> > index 553866751e1a..d2bb954cd54f 100644
> > --- a/arch/arm/kernel/Makefile
> > +++ b/arch/arm/kernel/Makefile
> > @@ -44,6 +44,11 @@ obj-$(CONFIG_CPU_IDLE)		+= cpuidle.o
> >  obj-$(CONFIG_ISA_DMA_API)	+= dma.o
> >  obj-$(CONFIG_FIQ)		+= fiq.o fiqasm.o
> >  obj-$(CONFIG_MODULES)		+= armksyms.o module.o
> > +ifeq ($(CONFIG_MODULES),y)
> > +obj-y				+= module_alloc.o
> > +else
> > +obj-$(CONFIG_KPROBES)		+= module_alloc.o
> > +endif
> 
> Doesn't:
> 
> obj-$(CONFIG_MODULES)		+= module_alloc.o
> obj-$(CONFIG_KPROBES)		+= module_alloc.o

That just begs for a new kconfig symbol for the object, and for
the object then to be built with it.

The archs which override the default can use ARCH_HAS_VM_ALLOC_EXEC.
Please note that the respective free is important as well and its
not clear if we need an another define for the free. Someone has
to do that work. We want to ensure to noexec the code on free and
this can vary on each arch.

> work just as well? The kbuild modules.rst documentation says:
> 
>         The order of files in $(obj-y) is significant.  Duplicates in
>         the lists are allowed: the first instance will be linked into
>         built-in.a and succeeding instances will be ignored.
> 
> so you should be fine... or the documentation is wrong!

Agreed, but this is just sloppy, better to use a new kconfig symbol
to represent what is actually being required.

  Luis