Re: [Qemu-devel] [PATCH] build: try improve handling of clang warnings

[Thomas Huth <thuth@redhat.com>]

On 09.03.2018 12:01, Gerd Hoffmann wrote:
> This patch disables the pragma diagnostic -Wunused-but-set-variable for
> clang in util/coroutine-ucontext.c.
> 
> This in turn allows us to remove it from the configure check, so the
> CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE will succeed for clang.
> 
> With that in place clang builds (linux) will use -Werror by default,
> which breaks the build due to warning about unaligned struct members.
> 
> Given that our structs are often dictated by the hardware qemu emulates
> and the file formats we use this can't be fixed easily, so I think it is
> reasonaable to turn off this warning.  Do so by adding
> -Wno-address-of-packed-member to our list of warning flags.
> 
> Now clang builds qemu without warnings.  Well, almost.  There are some
> left in the rdma code.  Leaving that to the rdma people.  All others can
> use --disable-rdma to workarounds this.
> 
> Cc: Thomas Huth <thuth@redhat.com>
> Cc: Peter Maydell <peter.maydell@linaro.org>
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
>  configure                 | 2 +-
>  util/coroutine-ucontext.c | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/configure b/configure
> index 6f3921c02a..5e4310b910 100755
> --- a/configure
> +++ b/configure
> @@ -1692,6 +1692,7 @@ gcc_flags="-Wno-missing-include-dirs -Wempty-body -Wnested-externs $gcc_flags"
>  gcc_flags="-Wendif-labels -Wno-shift-negative-value $gcc_flags"
>  gcc_flags="-Wno-initializer-overrides -Wexpansion-to-defined $gcc_flags"
>  gcc_flags="-Wno-string-plus-int $gcc_flags"
> +gcc_flags="-Wno-address-of-packed-member $gcc_flags"

Since the warning is sometimes also a good idea ... maybe it would
rather be better to use -Wno-error=address-of-packed-member instead?

Anyway, with or without that change:

Reviewed-by: Thomas Huth <thuth@redhat.com>