Re: [PATCH] xen/arm: Fix compilation error when early printk is enabled

[Julien Grall <julien@xxxxxxx>]

Hi Jan,

On 21/01/2021 10:24, Jan Beulich wrote:
> On 21.01.2021 10:56, Julien Grall wrote:
> > Hi Jan,
> >
> > On 21/01/2021 09:43, Jan Beulich wrote:
> > > On 21.01.2021 10:30, Michal Orzel wrote:
> > > > Fix compilation error when enabling early printk, introduced
> > > > by commit aa4b9d1ee6538b5cbe218d4d3fcdf9548130a063:
> > > > ```
> > > > debug.S: Assembler messages:
> > > > debug.S:31: Error: constant expression expected at operand 2 -- `ldr 
> > > > x15,=((0x00400000+(0)*PAGE_SIZE)+(0x1c090000&~PAGE_MASK))`
> > > > debug.S:38: Error: constant expression expected at operand 2 -- `ldr 
> > > > x15,=((0x00400000+(0)*PAGE_SIZE)+(0x1c090000&~PAGE_MASK))`
> > > > ```
> > > >
> > > > The fix is to include header <xen/page-size.h> which now contains
> > > > definitions for page/size/mask etc.
> > > >
> > > > Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
> > > I'm sorry for the breakage, but I wonder how I should have noticed
> > > the issue. In all the Arm .config-s I'm routinely building I can't
> > > even see ...
> > >
> > > > --- a/xen/include/asm-arm/early_printk.h
> > > > +++ b/xen/include/asm-arm/early_printk.h
> > > > @@ -10,6 +10,7 @@
> > > >    #ifndef __ARM_EARLY_PRINTK_H__
> > > >    #define __ARM_EARLY_PRINTK_H__
> > > >    
> > > > +#include <xen/page-size.h>
> > > >    
> > > >    #ifdef CONFIG_EARLY_PRINTK
> > > ... a respective Kconfig setting, i.e. it's not like I simply
> > > failed to enable it.
> > EARLY_PRINTK is defined in arch/arm/Kconfig.debug and is selected when
> > you specify the UART to use.
> >
> > Assuming you are only build testing, you could add the following for
> > testing EARLY_PRINTK:
> >
> > CONFIG_DEBUG=y
> > CONFIG_EARLY_UART_CHOICE_8250=y
> > CONFIG_EARLY_UART_8250=y
> > CONFIG_EARLY_PRINTK=y
> > CONFIG_EARLY_UART_BASE_ADDRESS=
> > CONFIG_EARLY_UART_8250_REG_SHIFT=0
> > CONFIG_EARLY_PRINTK_INC="debug-8250.inc"
> Ah yes, this works, thanks. The "optional" on the choice isn't
> very helpful I suppose, because when going from an existing
> .config one would neither find a setting presently turned off
> in that .config, nor will there be a prompt.
Do you have a suggestion how the "choice" can appear in the .config?

> I suppose any page-aligned base address is fine to use for my
> build-testing-only purposes?
The base address doesn't need to be page-aligned (some HW have multiple 
UARTs in the same 4K region).
Cheers,

--
Julien Grall