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Date: Mon, 12 Apr 2021 12:33:49 +0000 (UTC)
From: Michael Matz <matz@suse.de>
To: Tom de Vries <tdevries@suse.de>
cc: Mark Wielaard <mark@klomp.org>, dwz@sourceware.org, jakub@redhat.com
Subject: Re: [PATCH] Add -p native and -e native
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Hello,

On Fri, 9 Apr 2021, 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?

I think using readelf should work here.  But the patch has problems:

+#if NATIVE_ENDIAN == little
+#define NATIVE_ENDIAN_VAL __ORDER_LITTLE_ENDIAN__
+#elif NATIVE_ENDIAN == big
+#define NATIVE_ENDIAN_VAL __ORDER_LITTLE_ENDIAN__
+#else
+#define NATIVE_ENDIAN not available
+#define NATIVE_ENDIAN_VAL 0
+#endif

The preprocessor works different than you seem to assume.  Unknown tokens 
are replaced with 0, so what you've written is the same as:

+#if NATIVE_ENDIAN == 0
+#define NATIVE_ENDIAN_VAL __ORDER_LITTLE_ENDIAN__
+#elif NATIVE_ENDIAN == 0

(except if you have defined 'little' and 'big' somewhere, but I can't see 
that?)  Also __ORDER_LITTLE_ENDIAN__ is defined by GCC since 4.6, you 
might want to check defined-ness of it before using it.  And you're 
setting NATIVE_ENDIAN_VAL to little endian in both if arms.


Ciao,
Michael.