Re: [PATCH v9 5/8] x86/boot: Add get_acpi_rsdp() to parse RSDP in cmdlien from kexec

[Chao Fan]

On Mon, Oct 22, 2018 at 02:06:13PM +0800, Baoquan He wrote:
>On 10/22/18 at 05:30am, Fan, Chao wrote:
>> >> +static void get_acpi_rsdp(acpi_physical_address *rsdp_addr)
>> >> +{
>> >> +#ifdef CONFIG_KEXEC
>> >> +	unsigned long long res;
>> >> +	int len = 0;
>> >> +	char *val;
>> >> +
>> >> +	val = malloc(20);
>> >
>> >Why is the length 20? Defined a macro?
>> >
>> 
>> Not a calculation, if it's enough to store the address, that will be OK.
>
>Sorry, I didn't catch. It's 16 in setup_acpi_rsdp() of
>drivers/acpi/osl.c . What does 'that' mean?

The second parameter of kstrtoull(), the 16 you mentioned means
hexadecimal, not the length.
I checked my host and guest, the value are ACPI20=0xbfbfa014, ACPI20=0xdb807000.
The length of memory is 8. Well the max memory address is 16, add
"0x" and '\0' is 19. So I set it as 20.
I am not sure whether 8 is enough for the address, if OK, 11 will
be enough, or 19 is OK.
If my understanding is wrong, please tell me.

Thanks,
Chao Fan

>
>Wondering why not making it 200, it's also enough to store the address.
>
>