Re: [PATCH 7/8] x86/EFI: keep debug info in xen.efi

[Jan Beulich <jbeulich@xxxxxxxx>]

On 23.04.2021 12:07, Roger Pau Monné wrote:
> On Fri, Apr 23, 2021 at 10:51:40AM +0200, Jan Beulich wrote:
>> On 23.04.2021 09:30, Roger Pau Monné wrote:
>>> /*
>>>  * Explicitly list debug section for the PE output so that they don't
>>>  * end up at VA 0 which is below image base and thus invalid. Also use
>>>  * the NOLOAD directive, even when currently ignored by PE output, in
>>>  * order to note those sections shouldn't be loaded into memory.
>>>  *
>>>  * Note such sections are past _end, so if loaded will be discarded by
>>>  * Xen anyway.
>>>  */
>>>
>>> Feel free to reword or expand the comment.
>>
>> Yes, I've edited it some while inserting. Will see to get to
>> submitting v2 then.
>>
>>> Not sure there's some
>>> reference we could add here about how debug sections are placed in PE
>>> files usually.
>>
>> As said before - I don't think there's any "usually" here, which is
>> why different environments have invented different ways. The debug
>> info native to COFF is more like ELF's symbol table (with a little
>> bit of extra information) plus Dwarf's .debug_line, but not really
>> fully covering what you'd expect from debug info.
> 
> One last thing, do you know if the newly added debug_* sections get
> the IMAGE_SCN_MEM_DISCARDABLE section flag set?

At least with an up-to-date ld (i.e. one meeting the requirements so
we wouldn't force debug info to be stripped) they do.

> Not sure there's a way we can force it from the linker script TBH, but
> would be nice and seems to be a recommended flag for debug sections
> according to Microsoft [0].

The linker does this for debugging sections irrespective of what the
linker script says:

   if ((sec_flags & SEC_DEBUGGING) != 0)
     styp_flags |= IMAGE_SCN_MEM_DISCARDABLE;

Jan