[Qemu-devel] [PATCH] configure: mark qemu-ga VSS includes as system headers

[Qemu-devel] [PATCH] configure: mark qemu-ga VSS includes as system headers

[Michael Roth]

As of e4650c81, we do w32 builds with -Werror enabled. Unfortunately
for cases where we enable VSS support in qemu-ga, we still have
warnings generated by VSS includes that ship as part of the Microsoft
VSS SDK.

We can selectively address a number of these warnings using

  #pragma GCC diagnostic ignored ...

but at least one of these:

  warning: ‘typedef’ was ignored in this declaration

resulting from declarations of the form:

  typedef struct Blah { ... };

does not provide a specific command-line/pragma option to disable
warnings of the sort.

To allow VSS builds to succeed, the next-best option is disabling
these warnings on a per-file basis. pragmas like #pragma GCC
system_header can be used to declare subsequent includes/declarations
as being exempt from normal warnings, but this must be done within
a header file.

Since we don't control the VSS SDK, we'd need to rely on a
intermediate header include to accomplish this, and
since different objects in the VSS link target rely on different
headers from the VSS SDK, this would become somewhat of a rat's nest
(though not totally unmanageable).

The next step up in granularity is just marking the entire VSS
SDK include path as system headers via -isystem. This is a bit more
heavy-handed, but since this SDK hasn't changed since 2005, there's
likely little to be gained from selectively disabling warnings
anyway, so we implement that approach here.

This fixes the -Werror failures in both the configure test and the
qga build due to shared reliance on $vss_win32_include. For the
same reason, this also enforces a new dependency on -isystem support
in the C/C++ compiler when building QGA with VSS enabled.

Cc: Thomas Huth <thuth@redhat.com>
Cc: Stefan Weil <sw@weilnetz.de>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
---
 configure | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/configure b/configure
index e14e907..2d84bc5 100755
--- a/configure
+++ b/configure
@@ -4049,13 +4049,13 @@ fi
 
 if test "$mingw32" = "yes" -a "$guest_agent" != "no" -a "$vss_win32_sdk" != "no" ; then
   case "$vss_win32_sdk" in
-    "")   vss_win32_include="-I$source_path" ;;
+    "")   vss_win32_include="-isystem $source_path" ;;
     *\ *) # The SDK is installed in "Program Files" by default, but we cannot
           # handle path with spaces. So we symlink the headers into ".sdk/vss".
-          vss_win32_include="-I$source_path/.sdk/vss"
+          vss_win32_include="-isystem $source_path/.sdk/vss"
 	  symlink "$vss_win32_sdk/inc" "$source_path/.sdk/vss/inc"
 	  ;;
-    *)    vss_win32_include="-I$vss_win32_sdk"
+    *)    vss_win32_include="-isystem $vss_win32_sdk"
   esac
   cat > $TMPC << EOF
 #define __MIDL_user_allocate_free_DEFINED__
-- 
1.9.1

Re: [Qemu-devel] [PATCH] configure: mark qemu-ga VSS includes as system headers

[Thomas Huth]

On 29.06.2016 01:43, Michael Roth wrote:
> As of e4650c81, we do w32 builds with -Werror enabled. Unfortunately
> for cases where we enable VSS support in qemu-ga, we still have
> warnings generated by VSS includes that ship as part of the Microsoft
> VSS SDK.
> 
> We can selectively address a number of these warnings using
> 
>   #pragma GCC diagnostic ignored ...
> 
> but at least one of these:
> 
>   warning: ‘typedef’ was ignored in this declaration
> 
> resulting from declarations of the form:
> 
>   typedef struct Blah { ... };
> 
> does not provide a specific command-line/pragma option to disable
> warnings of the sort.
> 
> To allow VSS builds to succeed, the next-best option is disabling
> these warnings on a per-file basis. pragmas like #pragma GCC
> system_header can be used to declare subsequent includes/declarations
> as being exempt from normal warnings, but this must be done within
> a header file.
> 
> Since we don't control the VSS SDK, we'd need to rely on a
> intermediate header include to accomplish this, and
> since different objects in the VSS link target rely on different
> headers from the VSS SDK, this would become somewhat of a rat's nest
> (though not totally unmanageable).
> 
> The next step up in granularity is just marking the entire VSS
> SDK include path as system headers via -isystem. This is a bit more
> heavy-handed, but since this SDK hasn't changed since 2005, there's
> likely little to be gained from selectively disabling warnings
> anyway, so we implement that approach here.
> 
> This fixes the -Werror failures in both the configure test and the
> qga build due to shared reliance on $vss_win32_include. For the
> same reason, this also enforces a new dependency on -isystem support
> in the C/C++ compiler when building QGA with VSS enabled.

Did we ever support any non-GCC-based compiler for building QGA? I don't
think so, but in the worst case, we could later add a check whether the
compiler supports that parameter, too...

Anyway, I think your patch is a nice and clean way to deal with the
error messages from these headers, so:

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

Re: [Qemu-devel] [PATCH] configure: mark qemu-ga VSS includes as system headers

[Michael Roth]

Quoting Thomas Huth (2016-06-29 03:27:26)
> On 29.06.2016 01:43, Michael Roth wrote:
> > As of e4650c81, we do w32 builds with -Werror enabled. Unfortunately
> > for cases where we enable VSS support in qemu-ga, we still have
> > warnings generated by VSS includes that ship as part of the Microsoft
> > VSS SDK.
> > 
> > We can selectively address a number of these warnings using
> > 
> >   #pragma GCC diagnostic ignored ...
> > 
> > but at least one of these:
> > 
> >   warning: ‘typedef’ was ignored in this declaration
> > 
> > resulting from declarations of the form:
> > 
> >   typedef struct Blah { ... };
> > 
> > does not provide a specific command-line/pragma option to disable
> > warnings of the sort.
> > 
> > To allow VSS builds to succeed, the next-best option is disabling
> > these warnings on a per-file basis. pragmas like #pragma GCC
> > system_header can be used to declare subsequent includes/declarations
> > as being exempt from normal warnings, but this must be done within
> > a header file.
> > 
> > Since we don't control the VSS SDK, we'd need to rely on a
> > intermediate header include to accomplish this, and
> > since different objects in the VSS link target rely on different
> > headers from the VSS SDK, this would become somewhat of a rat's nest
> > (though not totally unmanageable).
> > 
> > The next step up in granularity is just marking the entire VSS
> > SDK include path as system headers via -isystem. This is a bit more
> > heavy-handed, but since this SDK hasn't changed since 2005, there's
> > likely little to be gained from selectively disabling warnings
> > anyway, so we implement that approach here.
> > 
> > This fixes the -Werror failures in both the configure test and the
> > qga build due to shared reliance on $vss_win32_include. For the
> > same reason, this also enforces a new dependency on -isystem support
> > in the C/C++ compiler when building QGA with VSS enabled.
> 
> Did we ever support any non-GCC-based compiler for building QGA? I don't
> think so, but in the worst case, we could later add a check whether the
> compiler supports that parameter, too...

Not really, but I think it's possible to bootstrap clang using mingw,
which is probably a reasonable option to keep open. That was the main
reason I wanted to point out the new dependency, but it turns out clang
supports -isystem anyway so a check/fallback in configure (like we
have for #pragma GCC diagnostic) is probably not not needed atm.

The other possibility is a native MSVC compile, but I doubt that works
as is (heavy usage of unistd.h, for instance), and I'm not aware of any
good reason to make it work.

> 
> Anyway, I think your patch is a nice and clean way to deal with the
> error messages from these headers, so:
> 
> Reviewed-by: Thomas Huth <thuth@redhat.com>

Thanks!

Re: [Qemu-devel] [PATCH] configure: mark qemu-ga VSS includes as system headers

[Michael Roth]

Quoting Michael Roth (2016-06-28 18:43:46)
> As of e4650c81, we do w32 builds with -Werror enabled. Unfortunately
> for cases where we enable VSS support in qemu-ga, we still have
> warnings generated by VSS includes that ship as part of the Microsoft
> VSS SDK.
> 
> We can selectively address a number of these warnings using
> 
>   #pragma GCC diagnostic ignored ...
> 
> but at least one of these:
> 
>   warning: ‘typedef’ was ignored in this declaration
> 
> resulting from declarations of the form:
> 
>   typedef struct Blah { ... };
> 
> does not provide a specific command-line/pragma option to disable
> warnings of the sort.
> 
> To allow VSS builds to succeed, the next-best option is disabling
> these warnings on a per-file basis. pragmas like #pragma GCC
> system_header can be used to declare subsequent includes/declarations
> as being exempt from normal warnings, but this must be done within
> a header file.
> 
> Since we don't control the VSS SDK, we'd need to rely on a
> intermediate header include to accomplish this, and
> since different objects in the VSS link target rely on different
> headers from the VSS SDK, this would become somewhat of a rat's nest
> (though not totally unmanageable).
> 
> The next step up in granularity is just marking the entire VSS
> SDK include path as system headers via -isystem. This is a bit more
> heavy-handed, but since this SDK hasn't changed since 2005, there's
> likely little to be gained from selectively disabling warnings
> anyway, so we implement that approach here.
> 
> This fixes the -Werror failures in both the configure test and the
> qga build due to shared reliance on $vss_win32_include. For the
> same reason, this also enforces a new dependency on -isystem support
> in the C/C++ compiler when building QGA with VSS enabled.
> 
> Cc: Thomas Huth <thuth@redhat.com>
> Cc: Stefan Weil <sw@weilnetz.de>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

Thanks, applied to qga tree:
  https://github.com/mdroth/qemu/commits/qga

> ---
>  configure | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/configure b/configure
> index e14e907..2d84bc5 100755
> --- a/configure
> +++ b/configure
> @@ -4049,13 +4049,13 @@ fi
>  
>  if test "$mingw32" = "yes" -a "$guest_agent" != "no" -a "$vss_win32_sdk" != "no" ; then
>    case "$vss_win32_sdk" in
> -    "")   vss_win32_include="-I$source_path" ;;
> +    "")   vss_win32_include="-isystem $source_path" ;;
>      *\ *) # The SDK is installed in "Program Files" by default, but we cannot
>            # handle path with spaces. So we symlink the headers into ".sdk/vss".
> -          vss_win32_include="-I$source_path/.sdk/vss"
> +          vss_win32_include="-isystem $source_path/.sdk/vss"
>           symlink "$vss_win32_sdk/inc" "$source_path/.sdk/vss/inc"
>           ;;
> -    *)    vss_win32_include="-I$vss_win32_sdk"
> +    *)    vss_win32_include="-isystem $vss_win32_sdk"
>    esac
>    cat > $TMPC << EOF
>  #define __MIDL_user_allocate_free_DEFINED__
> -- 
> 1.9.1
> 
>