Re: [PATCH v6 06/12] x86/hyperlaunch: obtain cmdline from device tree

[Jason Andryuk <jason.andryuk@amd.com>]

On 2025-06-10 02:56, Jan Beulich wrote:
> On 09.06.2025 19:07, Jason Andryuk wrote:
>> On 2025-04-29 08:36, Alejandro Vallejo wrote:
>>> From: "Daniel P. Smith" <dpsmith@apertussolutions.com>
>>>
>>> Add support to read the command line from the hyperlaunch device tree.
>>> The device tree command line is located in the "bootargs" property of the
>>> "multiboot,kernel" node.
>>>
>>> A boot loader command line, e.g. a grub module string field, takes
>>> precendence over the device tree one since it is easier to modify.
>>>
>>> Signed-off-by: Daniel P. Smith <dpsmith@apertussolutions.com>
>>> Signed-off-by: Jason Andryuk <jason.andryuk@amd.com>
>>> Signed-off-by: Alejandro Vallejo <agarciav@amd.com>
>>> Reviewed-by: Denis Mukhin <dmukhin@ford.com>
>>> ---
>>
>>> diff --git a/xen/common/domain-builder/fdt.c b/xen/common/domain-builder/fdt.c
>>> index cbb0ed30a2..dabe201b04 100644
>>> --- a/xen/common/domain-builder/fdt.c
>>> +++ b/xen/common/domain-builder/fdt.c
>>> @@ -219,6 +219,12 @@ static int __init fdt_process_domain_node(
>>>                printk(XENLOG_INFO "  kernel: multiboot-index=%d\n", idx);
>>>                bi->mods[idx].type = BOOTMOD_KERNEL;
>>>                bd->kernel = &bi->mods[idx];
>>> +
>>> +            /* If bootloader didn't set cmdline, see if FDT provides one. */
>>> +            if ( bd->kernel->cmdline_pa &&
>>> +                 !((char *)__va(bd->kernel->cmdline_pa))[0] )
>>
>> The logic is incorrect - it should be:
>>
>>              if ( !bd->kernel->cmdline_pa ||
>>                   !((char *)__va(bd->kernel->cmdline_pa))[0] )
>>
>> If there is no cmdline_pa (which happens with the "reg" property) or the if there is a 0-length string, then check the DT for bootargs.
> 
> Even that sounds bogus to me: There's a difference between "no command line"
> and "empty command line".

Yes, you have a point.  The difficulty is grub always provides a NUL 
terminated string, so Xen can't differentiate the two.

Regards,
Jason