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


  • To: Jan Beulich <jbeulich@xxxxxxxx>
  • From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • Date: Fri, 23 Apr 2021 12:07:07 +0200
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  • Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>
  • Delivery-date: Fri, 23 Apr 2021 10:07:26 +0000
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  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

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?

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].

Thanks, Roger.

[0] https://docs.microsoft.com/en-us/windows/win32/debug/pe-format#section-flags



 


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