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wasm: disable run-time check for specialHTMLTargets

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Recent versions of Emscripten may abort if module_property()
is used to look up specialHTMLTargets, which makes run-time
checking impossible. The abort is implemented on the JS property
getter on the Module object, which means that it's not possible
to bypass this by using e.g. EM_ASM instead of the C++ API.

Disable usage of specialHTMLTargets on emsdk > 3.1.14 for now,
until we can add API (or find some other means) for opting in.

This commit also adds functions for comparing Emscripten
versions.

Pick-to: 6.4
Change-Id: Ibe5d1a82f267fa95dd62cdfc66595bc23036933f
Reviewed-by: Aleksandr Reviakin <aleksandr.reviakin@qt.io>
Reviewed-by: Lorn Potter <lorn.potter@gmail.com>
This commit is contained in:
Morten Sørvig 2022-10-10 12:58:14 +02:00 committed by Morten Johan Sørvig
parent 683936d3cb
commit 4711f078b7
1 changed files with 38 additions and 0 deletions
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38
src/plugins/platforms/wasm/qwasmscreen.cpp
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@ -16,6 +16,8 @@
#include <QtGui/qguiapplication.h>
#include <private/qhighdpiscaling_p.h>
#include <tuple>
QT_BEGIN_NAMESPACE
using namespace emscripten;
@ -174,10 +176,46 @@ std::string QWasmScreen::canvasSpecialHtmlTargetId() const
return std::string("!qtcanvas_") + std::to_string(uintptr_t(this));
}
namespace {
// Compare Emscripten versions, returns > 0 if a is greater than b.
int compareVersionComponents(int a, int b)
{
return a >= 0 && b >= 0 ? a - b : 0;
}
int compareEmscriptenVersions(std::tuple<int, int, int> a, std::tuple<int, int, int> b)
{
if (std::get<0>(a) == std::get<0>(b)) {
if (std::get<1>(a) == std::get<1>(b)) {
return compareVersionComponents(std::get<2>(a), std::get<2>(b));
}
return compareVersionComponents(std::get<1>(a), std::get<1>(b));
}
return compareVersionComponents(std::get<0>(a), std::get<0>(b));
}
bool isEmsdkVersionGreaterThan(std::tuple<int, int, int> test)
{
return compareEmscriptenVersions(
std::make_tuple(__EMSCRIPTEN_major__, __EMSCRIPTEN_minor__, __EMSCRIPTEN_tiny__), test) > 0;
}
} // namespace
bool QWasmScreen::hasSpecialHtmlTargets() const
{
static bool gotIt = []{
// Enable use of specialHTMLTargets, if available
// On Emscripten > 3.1.14 (exact version not known), emscripten::val::module_property()
// aborts instead of returning undefined when attempting to resolve the specialHTMLTargets
// property, in the case where it is not defined. Disable the availability test in this case.
// FIXME: Add alternative way to enable.
if (isEmsdkVersionGreaterThan(std::make_tuple(3, 1, 14)))
return false;
emscripten::val htmlTargets = emscripten::val::module_property("specialHTMLTargets");
if (htmlTargets.isUndefined())
return false;