Re: [XEN PATCH v2 1/7] xen: add declarations for variables where needed

[Nicola Vetrini <nicola.vetrini@bugseng.com>]

On 17/10/2023 08:46, Jan Beulich wrote:
> On 16.10.2023 19:05, Nicola Vetrini wrote:
>> On 16/10/2023 16:50, Jan Beulich wrote:
>>> On 09.10.2023 08:54, Nicola Vetrini wrote:
>>>> --- a/xen/arch/x86/include/asm/compat.h
>>>> +++ b/xen/arch/x86/include/asm/compat.h
>>>> @@ -13,6 +13,7 @@ typedef unsigned long full_ptr_t;
>>>> 
>>>>  struct domain;
>>>>  #ifdef CONFIG_PV32
>>>> +extern unsigned long cr4_pv32_mask;
>>> 
>>> Why is this needed? Didn't we say declarations aren't needed when the
>>> only consumer is assembly code? (I also wonder how this header is any
>>> more "appropriate" - see the changelog entry - than about any other
>>> one.)
>>> 
>> 
>> It was pointed out to me [1] that compat.h might be more appropriate
>> than setup.h
>> (probably because the asm code referencing it is under x86_64/compat).
> 
> Hmm. I agree setup.h isn't appropriate.
> 
>> Further, while it's true that this variable is used in asm, it's also
>> used in x86/setup.c, hence
>> the need for a declaration.
> 
> But that's the file where the variable is defined. IOW no risk of
> definition and (non-existing) declaration going out of sync.
> 

This is an aspect specific to this variable, that unfortunately the rule 
does not
capture. I'll deviate this in the next version of this series.

>>>> --- a/xen/arch/x86/include/asm/setup.h
>>>> +++ b/xen/arch/x86/include/asm/setup.h
>>>> @@ -13,6 +13,7 @@ extern char __2M_rwdata_start[], 
>>>> __2M_rwdata_end[];
>>>>  extern unsigned long xenheap_initial_phys_start;
>>>>  extern uint64_t boot_tsc_stamp;
>>>> 
>>>> +extern char cpu0_stack[STACK_SIZE];
>>> 
>>> Same question here.
>>> 
>> 
>> This one is a bit more nuanced (I wouldn't oppose deviating this), but
>> there is indeed one use.
> 
> Still same here then.
> 

Same as above; it can be argued that there's no risk of anything going 
out of sync.

>>>> --- a/xen/common/symbols.c
>>>> +++ b/xen/common/symbols.c
>>>> @@ -21,23 +21,6 @@
>>>>  #include <xen/guest_access.h>
>>>>  #include <xen/errno.h>
>>>> 
>>>> -#ifdef SYMBOLS_ORIGIN
>>>> -extern const unsigned int symbols_offsets[];
>>>> -#define symbols_address(n) (SYMBOLS_ORIGIN + symbols_offsets[n])
>>>> -#else
>>>> -extern const unsigned long symbols_addresses[];
>>>> -#define symbols_address(n) symbols_addresses[n]
>>>> -#endif
>>>> -extern const unsigned int symbols_num_syms;
>>>> -extern const u8 symbols_names[];
>>>> -
>>>> -extern const struct symbol_offset symbols_sorted_offsets[];
>>>> -
>>>> -extern const u8 symbols_token_table[];
>>>> -extern const u16 symbols_token_index[];
>>>> -
>>>> -extern const unsigned int symbols_markers[];
>>>> -
>>>>  /* expand a compressed symbol data into the resulting uncompressed
>>>> string,
>>>>     given the offset to where the symbol is in the compressed stream
>>>> */
>>>>  static unsigned int symbols_expand_symbol(unsigned int off, char
>>>> *result)
>>>> --- a/xen/include/xen/symbols.h
>>>> +++ b/xen/include/xen/symbols.h
>>>> @@ -33,4 +33,22 @@ struct symbol_offset {
>>>>      uint32_t stream; /* .. in the compressed stream.*/
>>>>      uint32_t addr;   /* .. and in the fixed size address array. */
>>>>  };
>>>> +
>>>> +#ifdef SYMBOLS_ORIGIN
>>>> +extern const unsigned int symbols_offsets[];
>>>> +#define symbols_address(n) (SYMBOLS_ORIGIN + symbols_offsets[n])
>>>> +#else
>>>> +extern const unsigned long symbols_addresses[];
>>>> +#define symbols_address(n) symbols_addresses[n]
>>>> +#endif
>>>> +extern const unsigned int symbols_num_syms;
>>>> +extern const u8 symbols_names[];
>>>> +
>>>> +extern const struct symbol_offset symbols_sorted_offsets[];
>>>> +
>>>> +extern const u8 symbols_token_table[];
>>>> +extern const u16 symbols_token_index[];
>>>> +
>>>> +extern const unsigned int symbols_markers[];
>>>> +
>>>>  #endif /*_XEN_SYMBOLS_H*/
>>> 
>>> This change is even less clear to me: The producer is assembly code,
>>> and the consumer already had appropriate declarations. Why would we
>>> want to increase the scope of their visibility?
>> 
>> The missing decls are about common/symbols-dummy.c. Xen can choose 
>> that
>> this file does
>> not need to conform (to this guideline or any guideline), in which 
>> case
>> this change can be dropped.
> 
> Since symbols-dummy.c isn't used in the final binary, I'd prefer that.
> Otherwise imo a new private header used by just the two files would 
> want
> introducing, to keep exposure limited.
> 
> Jan

Ok

-- 
Nicola Vetrini, BSc
Software Engineer, BUGSENG srl (https://bugseng.com)