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

From: Peter Maydell
Subject: Re: [Qemu-devel] [RFC PATCH qemu] dtc: Allow compiling with old gcc
Date: Wed, 8 Mar 2017 15:21:43 +0100

On 8 March 2017 at 13:49, Alexey Kardashevskiy <address@hidden> 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
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

-- PMM

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