Re: [PATCH] x86/build32: Discard all orphaned sections

[Jan Beulich <jbeulich@xxxxxxxx>]

On 13.05.2020 17:00, Andrew Cooper wrote:
> On 13/05/2020 10:13, Jan Beulich wrote:
>> [CAUTION - EXTERNAL EMAIL] DO NOT reply, click links, or open attachments 
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>>
>> On 12.05.2020 21:11, Andrew Cooper wrote:
>>> @@ -47,6 +47,14 @@ SECTIONS
>>>           *
>>>           * Please check build32.mk for more details.
>>>           */
>>> -        /* *(.got.plt) */
>>> +        *(.got.plt)
>>> +  }
>>> +
>>> +  /DISCARD/ : {
>>> +        /*
>>> +         * Discard everything else, to prevent linkers from putting
>>> +         * orphaned sections ahead of .text, which needs to be first.
>>> +         */
>>> +        *(*)
>>>    }
>>>  }
>> To be honest I'm not sure if this isn't going too far. Much
>> depends on what would happen if a new real section appeared
>> that needs retaining.
> 
> Anything which is important enough will result in a linker error.
> 
>> Granted the linker may then once again
>> put it at the beginning of the image, and we'll be screwed
>> again, just like we'll be screwed if a section gets discarded
>> by mistake.
> 
> This way is more likely to result in a build failure than an inability
> to boot the resulting build of Xen.
> 
>> But it would be really nice if we had a way to
>> flag the need to play with the linker script. Hence perhaps
>> on new enough tool chains we indeed may want to make use of
>> --orphan-handling= ? And then discard just .note and .note.*
>> here?
> 
> The only valid option would be =error, but experimenting with that yields
> 
> ld: error: unplaced orphan section `.comment' from `cmdline.o'
> ld: error: unplaced orphan section `.note.GNU-stack' from `cmdline.o'
> ld: error: unplaced orphan section `.note.gnu.property' from `cmdline.o'
> ld: error: unplaced orphan section `.rel.got' from `cmdline.o'
> ld: error: unplaced orphan section `.got' from `cmdline.o'
> ld: error: unplaced orphan section `.got.plt' from `cmdline.o'
> ld: error: unplaced orphan section `.iplt' from `cmdline.o'
> ld: error: unplaced orphan section `.rel.iplt' from `cmdline.o'
> ld: error: unplaced orphan section `.igot.plt' from `cmdline.o'
> 
> which I think is going to get us massively bogged down in toolchain
> specifics.  I'm not entirely convinced this would be a good move.

That's ugly indeed; especially the .rel.* sections are worrying to
appear there. Hence patch as is
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>

Jan