Re: [PATCH] Add -p native and -e native

[Tom de Vries <tdevries@suse.de>]

On 4/12/21 10:14 PM, Mark Wielaard wrote:
> Hi,
> 
> On Fri, Apr 09, 2021 at 05:58:34PM +0200, Tom de Vries wrote:
>>>> Except for this narrow multilib case, doesn't this actually make it 
>>>> impossible to do a cross-arch build?
>>>
>>> For cross the term "native" doesn't make sense, so it would seem valid to 
>>> simply not support that setting with a cross (not multilib) dwz.  I.e. if 
>>> ./native can't be executed assume cross-ness and don't support -p native.
>>
>> I've tried yet another variant.  Instead of trying to generate an
>> executable and execute it, we generate an object and test properties
>> using readelf.
>>
>> This should no longer have the cross-build problem.
>>
>> WDYT?
> 
> Can we take a step back, because I think I lost the plot, sorry.
> 

Sure, of course.

> Why are we going through all this?
> 
> So with this when something is build as 32bit it can use 64bit as
> "native" pointer size. Or if something is cross compiled to
> little-endian it can still report big-endian as "native",
> 

Yes.  Native is defined by the current implementation as the default
endiannes and pointer size of code generated by the compiler used to
compile dwz.

So if you're using a compiler that by default generates 32-bit while
targeting 64-bit platform, then the resulting -p native is 32-bit.

> But when does that ever make sense?

It doesn't.

The current implementation makes sense if you use a native compiler
(i.e., generates 64-bit code for a 64-bit platform), and the same holds
in a cross-compiling scenario.

I think the assumption that was made here is that the implementation is
good enough if it gives good results for the native compiler scenario.

> Why would one run the 32bit
> binary on a 64bit system and wanting the default -p native be 64bit
> instead of 32bit? 

No idea why one would want to run the 32-bit binary on a 64bit system in
the first place.  But it's possible.

If we have an option -p/-e native, it needs to be assigned a semantics
in that case.

And in the case of using a native compiler, the semantics are accurate.

> Wouldn't one install and run the actual "native"
> 64-bit binary in that case?

Yes, that's what I would do.

Thanks,
- Tom