From 0eb7058b473069a04cde60a800dfd04148c0c8b1 Mon Sep 17 00:00:00 2001
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From: Yann E. MORIN <yann.morin.1998@free.fr>
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Date: Sat, 14 Dec 2020 21:15:17 +0100
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Subject: [PATCH] plugins/eglfs/gbm: don't FTBFS when EGLNativeDisplayType is not a pointer
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On some platforms, EGLNativeDisplayType is not a pointer, but some kind
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of integer, like an int (e.g. TI's SGX) or an unsigned int. In those
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cases, the build breaks with:
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qeglfskmsgbmintegration.cpp: In member function ‘virtual void* QEglFSKmsGbmIntegration::createDisplay(EGLNativeDisplayType)’:
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qeglfskmsgbmintegration.cpp:83:60: error: invalid conversion from ‘EGLNativeDisplayType’ {aka ‘int’} to ‘void*’ [-fpermissive]
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83 | display = getPlatformDisplay(EGL_PLATFORM_GBM_KHR, nativeDisplay, nullptr);
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| ^~~~~~~~~~~~~
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| |
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| EGLNativeDisplayType {aka int}
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We fix that by casting nativeDisplay to void* as expected by
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getPlatformDisplay().
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We can do that, because usually, nativeDisplay is already a pointer, and
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thus this cast is a no-op. When it is not already a pointer, we either
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don't care because the code path will not be taken at runtime, or the
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integer really is an opaque handle to some internal, low-level memory
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management, much like a void* is an pointer to an opaque memory type...
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It is to be noted, though, that in some ABIs (like x32), the size of a
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nativeDisplay that is not already a pointer, might be bigger than that
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of a pointer. There is not much we can do here anyway, since there would
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be no way to fit that in a void* to begin with, and the build will still
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fail for those situations. Those types of ABIs are far frome being
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widespread, the most prominent one, x32, even being retired...
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To be noted further: a more usual solution (as suggested in QTBUG-72567
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or in Gerrit:248270) would be to first cast to a qintptr or a quintptr,
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before finally casting to a void*. However, casting to either (resp.)
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qintptr or quintptr first, risk the case that nativeDisplay is of the other
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kind of signedness, (resp.) unsigned or signed, which would also cause
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some compile-time breakage.
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Finally, if nativeDisplay is something that is not an int-like, and that
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can't be cast into a void*, this would be hugely weird, so much so, that
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we do not even attempt to catter for that case.
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Fixes: QTBUG-72567
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Inspired-by: https://codereview.qt-project.org/c/qt/qtbase/+/248270
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Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
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---
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diff --git a/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms/qeglfskmsgbmintegration.cpp b/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms/qeglfskmsgbmintegration.cpp
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index d495a8d..059a580 100644
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--- a/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms/qeglfskmsgbmintegration.cpp
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+++ b/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms/qeglfskmsgbmintegration.cpp
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@@ -80,7 +80,9 @@
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}
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if (getPlatformDisplay) {
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- display = getPlatformDisplay(EGL_PLATFORM_GBM_KHR, nativeDisplay, nullptr);
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+ // EGLNativeDisplayType may be int on some platforms but those
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+ // won't hit this path. Have to keep it compiling nonetheless.
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+ display = getPlatformDisplay(EGL_PLATFORM_GBM_KHR, reinterpret_cast<void *>(nativeDisplay), nullptr);
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} else {
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qCDebug(qLcEglfsKmsDebug, "No eglGetPlatformDisplay for GBM, falling back to eglGetDisplay");
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display = eglGetDisplay(nativeDisplay);
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