Re: [PATCH v5 10/10] powerpc/fsl_booke/kaslr: dump out kernel offset information on panic

[Jason Yan]

On 2019/8/7 21:03, Michael Ellerman wrote:
> Jason Yan <yanaijie@xxxxxxxxxx> writes:
> > When kaslr is enabled, the kernel offset is different for every boot.
> > This brings some difficult to debug the kernel. Dump out the kernel
> > offset when panic so that we can easily debug the kernel.
>
> Some of this is taken from the arm64 version right? Please say so when
> you copy other people's code.

No problem. Architectures like x86 or arm64 or s390 both have this
similar code. I guess x86 is the first one.

> > diff --git a/arch/powerpc/kernel/machine_kexec.c b/arch/powerpc/kernel/machine_kexec.c
> > index c4ed328a7b96..078fe3d76feb 100644
> > --- a/arch/powerpc/kernel/machine_kexec.c
> > +++ b/arch/powerpc/kernel/machine_kexec.c
> > @@ -86,6 +86,7 @@ void arch_crash_save_vmcoreinfo(void)
> >   	VMCOREINFO_STRUCT_SIZE(mmu_psize_def);
> >   	VMCOREINFO_OFFSET(mmu_psize_def, shift);
> >   #endif
> > +	vmcoreinfo_append_str("KERNELOFFSET=%lx\n", kaslr_offset());
> >   }
>
> There's no mention of that in the commit log.
>
> Please split it into a separate patch and describe what you're doing and
> why.

OK

> > diff --git a/arch/powerpc/kernel/setup-common.c b/arch/powerpc/kernel/setup-common.c
> > index 1f8db666468d..064075f02837 100644
> > --- a/arch/powerpc/kernel/setup-common.c
> > +++ b/arch/powerpc/kernel/setup-common.c
> > @@ -715,12 +715,31 @@ static struct notifier_block ppc_panic_block = {
> >   	.priority = INT_MIN /* may not return; must be done last */
> >   };
> >   
> > +/*
> > + * Dump out kernel offset information on panic.
> > + */
> > +static int dump_kernel_offset(struct notifier_block *self, unsigned long v,
> > +			      void *p)
> > +{
> > +	pr_emerg("Kernel Offset: 0x%lx from 0x%lx\n",
> > +		 kaslr_offset(), KERNELBASE);
> > +
> > +	return 0;
> > +}
> > +
> > +static struct notifier_block kernel_offset_notifier = {
> > +	.notifier_call = dump_kernel_offset
> > +};
> > +
> >   void __init setup_panic(void)
> >   {
> >   	/* PPC64 always does a hard irq disable in its panic handler */
> >   	if (!IS_ENABLED(CONFIG_PPC64) && !ppc_md.panic)
> >   		return;
> >   	atomic_notifier_chain_register(&panic_notifier_list, &ppc_panic_block);
>
> > +	if (IS_ENABLED(CONFIG_RANDOMIZE_BASE) && kaslr_offset() > 0)
> > +		atomic_notifier_chain_register(&panic_notifier_list,
> > +					       &kernel_offset_notifier);
>
> Don't you want to do that before the return above?

Eagle eye. This should not affected by the conditions above.

> >   }
>
> cheers
>
> .