qt5: Disable pkg-config usage for cross-building

Some Qt sub-projects use pkg-config to recover compiler and linker flags. Among other things include paths will be pulled in CFLAGS.

What's interesting Qt tries to play smart and convert include paths from simple "-I" to "-isystem" if they match ones returned by [1] ---------------------------->8--------------------------- XXX/output/host/usr/bin/yyy-buildroot-linux-g++ --sysroot=XXX/output/host/usr/yyy-buildroot-linux/sysroot

(quoted diff) +0 -3

-pipe -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64
-Os  -xc++ -E -v - < /dev/null
---------------------------->8---------------------------

Most probably that [2] was done to mute tons of warnings generated for "system" headers. But commit message gives no hint here :(

So Qt's subprojects [and 3-rd party apps written on Qt] may end-up having "-system ZZZ" in their Makefile. That's all right until an application wants to use an STL header that includes for example "stdlib.h" with gcc 6.x, see what happens then [3].

That fixes building of Qt5Webkit on ARM with gcc 6.x, see [4].

[1] http://code.qt.io/cgit/qt/qtbase.git/tree/configure?h=5.6.1#n3660
[2] http://code.qt.io/cgit/qt/qtbase.git/commit?id=0b144bc76a368ecc6c5c1121a1b51e888a0621ac
[3] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70129
[4] http://lists.busybox.net/pipermail/buildroot/2016-September/172666.html

Signed-off-by Alexey Brodkin <[email protected]>

Cc Thomas Petazzoni <[email protected]>

Cc Peter Seiderer <[email protected]>

Cc Julien Corjon <[email protected]>

Cc "Yann E. MORIN" <[email protected]>

---
 package/qt5/qt5base/qt5base.mk | 1 +
 1 file changed, 1 insertion(+)

package/qt5/qt5base/qt5base.mk +0 -0

index bf541b0..2c52e2c 100644

package/qt5/qt5base/qt5base.mk +0 -0

 	-shared
 
 # Uses libgbm from mesa3d

Signature · 1 line

2.7.4

I have not paid much attention to the previous discussion on the topic.

However, I think disabling use of pkg-config is wrong. That is qmake that is at fault here because, from what I understood from the previous discussion, it emits -isystem where it should not.

So qmake needs to be fixed to not emit -isystem in those conditions.

Removing the use of pkg-config is just papering over the real problem.

Usually, using pkg-config solves more issues than not using it.

So, I am not very happy with this patch, to say the least... :-(

Hello,

Quoted 13 lines · Yann E. MORIN

I have not paid much attention to the previous discussion on the topic.

However, I think disabling use of pkg-config is wrong. That is qmake that is at fault here because, from what I understood from the previous discussion, it emits -isystem where it should not.

So qmake needs to be fixed to not emit -isystem in those conditions.

Removing the use of pkg-config is just papering over the real problem.

Usually, using pkg-config solves more issues than not using it.

Quoted 1 line

So, I am not very happy with this patch, to say the least... :-(

I entirely agree with Yann. Disabling pkg-config is clearly not the solution we want to use.

Alexey, have you tried the other approaches I outlined in the thread where the initial discussion took place?

Quoted 2 lines

Alexey, have you tried the other approaches I outlined in the thread where the initial discussion took place?

Well I don't like removal of pkg-config usage either but... Another approach with setting?QMAKE_CFLAGS_ISYSTEM to "" may work as well (even thought I haven't tried it yet) but that will mean people using buildroot-built toolchain for building their Qt5 apps will see those compiler warnings about "wrong" stuff in system headers. In the end that's why this "-isystem" was introduced in the first place.

Hello,

Quoted 11 lines · Alexey Brodkin

Quoted 4 lines

Alexey, have you tried the other approaches I outlined in the thread where the initial discussion took place???

Well I don't like removal of pkg-config usage either but... Another approach with setting?QMAKE_CFLAGS_ISYSTEM to "" may work as well (even thought I haven't tried it yet) but that will mean people using buildroot-built toolchain for building their Qt5 apps will see those compiler warnings about "wrong" stuff in system headers. In the end that's why this "-isystem" was introduced in the first place.

Which warning will they see? I don't quite get why they would see a warning,

and still fail to understand why qmake uses -isystem.

Hi Thomas,

Quoted 11 lines · Thomas Petazzoni

Hello,

Quoted 6 lines · Alexey Brodkin

Quoted 6 lines

Alexey, have you tried the other approaches I outlined in the thread where the initial discussion took place???

Hi Thomas, Yann,

Quoted 13 lines · Alexey Brodkin

Hi Thomas,

Quoted 10 lines · Thomas Petazzoni

Hello,

Quoted 5 lines · Alexey Brodkin

Quoted 5 lines

Alexey, have you tried the other approaches I outlined in the

thread

Quoted 1 line

Quoted 1 line

Quoted 1 line

Quoted 1 line

where the initial discussion took place?

Ok approach with setting empty QMAKE_CFLAGS_ISYSTEM works for me.

So what about something like that?
-------------------------->8---------------------

package/qt5/qt5base/qmake. renamed from package/qt5/qt5base/qmake.conf +0 -0

conf
index 2152d3c..49cf898 100644

package/qt5/qt5base/qmake.conf +1 -2

@@ -19,6 +19,7 @@ QMAKE_CXXFLAGS_RELEASE += -O3
 CONFIG                 += nostrip
 
 QMAKE_LIBS             += -lrt -lpthread -ldl
+QMAKE_CFLAGS_ISYSTEM   =
 
 include(../common/linux_device_post.conf)
 load(qt_config)
-------------------------->8---------------------
 
-Alexey

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