linux-kernel - Re: [PATCH v9 07/11] arm64: kexec

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Date:   Fri, 18 May 2018 18:58:48 +0900
From:   AKASHI Takahiro <takahiro.akashi@...aro.org>
To:     James Morse <james.morse@....com>
Cc:     catalin.marinas@....com, will.deacon@....com, dhowells@...hat.com,
        vgoyal@...hat.com, herbert@...dor.apana.org.au,
        davem@...emloft.net, dyoung@...hat.com, bhe@...hat.com,
        arnd@...db.de, ard.biesheuvel@...aro.org, bhsharma@...hat.com,
        kexec@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 07/11] arm64: kexec_file: add crash dump support

On Wed, May 16, 2018 at 09:34:41AM +0100, James Morse wrote:
> Hi Akashi,
> 
> On 15/05/18 18:11, James Morse wrote:
> > On 25/04/18 07:26, AKASHI Takahiro wrote:
> >> Enabling crash dump (kdump) includes
> >> * prepare contents of ELF header of a core dump file, /proc/vmcore,
> >>   using crash_prepare_elf64_headers(), and
> >> * add two device tree properties, "linux,usable-memory-range" and
> >>   "linux,elfcorehdr", which represent repsectively a memory range
> >>   to be used by crash dump kernel and the header's location
> 
> >> diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
> >> index 37c0a9dc2e47..ec674f4d267c 100644
> >> --- a/arch/arm64/kernel/machine_kexec_file.c
> >> +++ b/arch/arm64/kernel/machine_kexec_file.c
> >> @@ -76,6 +81,78 @@ int arch_kexec_walk_mem(struct kexec_buf *kbuf,
> 
> >> +static void fill_property(void *buf, u64 val64, int cells)
> >> +{
> >> +	u32 val32;
> >> +
> >> +	if (cells == 1) {
> >> +		val32 = cpu_to_fdt32((u32)val64);
> >> +		memcpy(buf, &val32, sizeof(val32));
> >> +	} else {
> > 
> >> +		memset(buf, 0, cells * sizeof(u32) - sizeof(u64));
> >> +		buf += cells * sizeof(u32) - sizeof(u64);
> > 
> > Is this trying to clear the 'top' cells and shuffle the pointer to point at the
> > 'bottom' 2? I'm pretty sure this isn't endian safe.
> 
> It came to me at 2am: this only works on big-endian, which is exactly what you
> want as that is the DT format.

Oops, I was almost tricked as I haven't tested kexec on BE
for a long time :)

Thanks,
-Takahiro AKASHI

> 
> > Do we really expect a system to have #address-cells > 2?
> 
> 
> Thanks,
> 
> James