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Re: [Xen-devel] [PATCH 2/4] x86/page: Remove bifurcated PAGE_HYPERVISOR constant
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Wed, 15 Jan 2020 12:53:41 +0000
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- Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Wed, 15 Jan 2020 12:53:58 +0000
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On 14/01/2020 16:25, Jan Beulich wrote:
>> --- a/xen/include/asm-x86/x86_64/page.h
>> +++ b/xen/include/asm-x86/x86_64/page.h
>> @@ -172,18 +172,11 @@ static inline intpte_t put_pte_flags(unsigned int x)
>> #define PAGE_HYPERVISOR_RX (__PAGE_HYPERVISOR_RX | _PAGE_GLOBAL)
>> #define PAGE_HYPERVISOR_RWX (__PAGE_HYPERVISOR | _PAGE_GLOBAL)
>>
>> -#ifdef __ASSEMBLY__
>> -/* Dependency on NX being available can't be expressed. */
>> -# define PAGE_HYPERVISOR PAGE_HYPERVISOR_RWX
>> -# define PAGE_HYPERVISOR_UCMINUS (__PAGE_HYPERVISOR_UCMINUS | _PAGE_GLOBAL)
>> -# define PAGE_HYPERVISOR_UC (__PAGE_HYPERVISOR_UC | _PAGE_GLOBAL)
>> -#else
>> # define PAGE_HYPERVISOR PAGE_HYPERVISOR_RW
>> # define PAGE_HYPERVISOR_UCMINUS (__PAGE_HYPERVISOR_UCMINUS | \
>> _PAGE_GLOBAL | _PAGE_NX)
>> # define PAGE_HYPERVISOR_UC (__PAGE_HYPERVISOR_UC | \
>> _PAGE_GLOBAL | _PAGE_NX)
> ... I'm afraid the assembler error resulting from someone actually
> (and mistakenly) using one of the constants making use of _PAGE_NX
> is going to be rather cryptic. Which in turn may motivate people
> to actually try to make _PAGE_NX "work" in assembly code. Therefore
> I'd like to ask that together with the changes here _PAGE_NX's
> #define be framed by #ifndef __ASSEMBLY__, such that any
> diagnostic, if it mentions a symbol name, would name the actual
> problem, rather than a derived one.
I can do this, but it doesn't make the error any less cryptic.
With _PAGE_NX hidden:
head.S: Assembler messages:
head.S:677: Error: invalid operands (*ABS* and *UND* sections) for `|'
With it visible:
head.S: Assembler messages:
head.S:677: Error: invalid character '?' in operand 1
I'm not aware of any way to get a useful symbol name out of the error.
~Andrew
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