Re: [Qemu-devel] [RFC PATCH qemu] dtc: Allow compiling with old gcc

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Mar 09, 2017 at 11:52:17AM +1100, Alexey Kardashevskiy wrote:
> On 09/03/17 01:21, Peter Maydell wrote:
> > On 8 March 2017 at 13:49, Alexey Kardashevskiy <aik@ozlabs.ru> wrote:
> >> After 6e85fce0225f "dtc: Update requirement to v1.4.2" QEMU stopped
> >> compiling in CentOS7:
> >>
> >> In file included from /home/aik/p/qemu/dtc/libfdt/libfdt.h:54:0,
> >>                  from /home/aik/p/qemu/device_tree.c:30:
> >> /home/aik/p/qemu/dtc/libfdt/libfdt_env.h:64:0: error: "__bitwise" redefined [-Werror]
> >>  #define __bitwise
> >>  ^
> >> In file included from /usr/include/asm/ptrace.h:27:0,
> >>                  from /usr/include/asm/sigcontext.h:11,
> >>                  from /usr/include/bits/sigcontext.h:27,
> >>                  from /usr/include/signal.h:340,
> >>                  from /home/aik/p/qemu/include/qemu/osdep.h:86,
> >>                  from /home/aik/p/qemu/device_tree.c:14:
> >> /usr/include/linux/types.h:21:0: note: this is the location of the previous definition
> >>  #define __bitwise __bitwise__
> >>  ^
> >> cc1: all warnings being treated as errors
> >> make: *** [device_tree.o] Error 1
> >> make: *** Waiting for unfinished jobs....
> >>
> >> The reason is that CentOS7 comes with libfdt 1.4.0 so QEMU tries using
> >> the internal one which does not compile as CentOS7 comes with gcc v4.8.5
> >> which reports warnings which it would not if the OS's libfdt was used
> >> (libfdt_env.h has not changed between 1.4.0 and 1.4.2).
> >>
> >> gcc 6.2.0 from Ubuntu v16.10 handles this fine.
> >>
> >> This replaces -I with -isystem to suppress the warning (which turns
> >> to an error because of -Werror).
> > 
> > Thanks for the bug report. I think it would be cleaner to fix this
> 
> Agree.
> 
> > by fixing the problem upstream in libfdt and then moving our
> > submodule forward to the fixed version. (libfdt should not be
> > defining __ prefixed symbols as these are reserved for the
> > system.)

Yes.  I've now fixed this in upstream libfdt, at Paolo's suggestion.
Unfortunately, it came just after the 1.4.3 release.  I was just leery
about making a new release and qemu pull so soon after the last one.
Should I do that anyway?

> Also agree, regardless my proposal, libfdt should be fixed. However v2.9
> won't compile on CentOS7 (and I suppose on RHEL7) which is a bit annoying.
> And having "-isystem" makes some sense as these headers are normally system
> ones and I'd think they should be treated the same way (i.e. path should be
> included via -isystem vs. -I).

I'm not really clear on why -isystem fixes this problem anyway.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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