Hi,
Emscripten uses clang/LLVM and not gcc, if makes any difference to you.
Setting /etc/alternatives has no effect on emscripten as essentially we
are cross compiling.
Perhaps you might try adding
CONFIG += c++17
If you are using c++-17 ?
emcc -v
$> emcc -v
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld)
2.0.14
clang version 13.0.0
(/opt/s/w/ir/cache/git/chromium.googlesource.com-external-github.com-llvm-llvm--project
5f3c99085d4c2ebf57fd0586b013b02e32a8e20b)
Target: wasm32-unknown-emscripten
Thread model: posix
On 27/12/2021 9:56 PM, Axel Spoerl wrote:
I can narrow down the issue as follows:
The problem at hand occurs on a compile server, compiling desktop
executables for Qt 5.15.2 (with GCC-7), Qt 6.2.2 (with GCC-9). To make
both configurations work, QMAKE_CXX=g++-7 / QMAKE_CXX=g++-9 arguments
are added in the respective Qt Creator build steps (which is necessary
for Qt 6.2.2 even if g++-9 is specified as compiler in the kit itself).
Emscripten (intended as a 3rd compile target) has been installed
according to https://doc.qt.io/qt-6/wasm.html
<https://doc.qt.io/qt-6/wasm.html> and
https://emscripten.org/docs/getting_started/index.html
<https://emscripten.org/docs/getting_started/index.html>
The emscripten installation is able to compile the latest openssl pulled
from github.
No matter which GCC version is chosen in /etc/alternatives and no matter
which emscripten version is activated (3.0.1 or 2.0.14):
.../upstream/emscripten/cache/sysroot/include/c++ only contains the v1
directory.
The server's /usr/include/c++ contains v1, 7 and 9 according to the GCC
versions installed. This is where my emscripten knowledge ends and I can
only experiment (e.g. by manually linking the 9 directory into the
emscripten cache, which is being ignored).
Compiling basic C++ code with #include <cmath> works for GCC 7 and
produces the errors mentioned earlier for GCC 9 (i.e. Qt 6.2.2).
Makefiles are generated by qmake out of a single .pro file. The .pro
file contains a WASM specific section to link against its own libcrypto
and libssl. Apart from the compilers used, all Makefiles look almost
identical.
=> It appears to me as if emscripten uses a default GCC version, which
in case of GCC 9 being expected is the wrong one. This leads to the lib
incompatibility as described by Thiago. I have not found options for
em++, 'emsdk install' or 'emsdk activate', that provide a GCC selection.
That may well be attributable to a lack of knowledge on my side.
> Well, Qt is a bit relevant if the qt-cmake of the Qt 6.2.2 WASM
installation
> results in broken make files.
>
> So the question is perhaps: Axel, assuming that you installed emscripten
> following the instruction and that you can verify that you can compile
> basic C++ code as Thiago suggested, how do you then generate your make
> files?
>
> Volker
>
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Lorn Potter
Freelance Qt Developer. Platform Maintainer Qt WebAssembly, Maintainer
QtSensors
Author, Hands-on Mobile and Embedded Development with Qt 5
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