Source/WebCore/platform/Length.cpp fails to build on PPC

[Jeremy Huddleston Sequoia]

This was first discovered in MacPorts when building webkit-gtk-1.8.3:

https://trac.macports.org/ticket/35989

The source builds fine for i386 and x86_64 but fails to build for ppc.  This compile-time assert fails:
COMPILE_ASSERT(sizeof(Length) == sizeof(SameSizeAsLength), length_should_stay_small);

libtool: compile:  /usr/bin/g++-4.2 -DHAVE_CONFIG_H -I. -DBUILDING_WEBKIT -Wall -W -Wcast-align -Wchar-subscripts -Wreturn-type -Wformat -Wformat-security -Wno-format-y2k -Wundef -Wmissing-format-attribute -Wpointer-arith -Wwrite-strings -Wno-unused-parameter -Wno-parentheses -fno-exceptions -DENABLE_GLIB_SUPPORT=1 -DBUILDING_CAIRO__=1 -DBUILDING_GTK__=1 -DWTF_CHANGES -DXP_UNIX -DWTF_USE_ICU_UNICODE=1 -DWTF_USE_GSTREAMER=1 -DGTK_API_VERSION_2=1 -DNDEBUG -I./Source/ThirdParty/ANGLE/src -I./Source/ThirdParty/ANGLE/include -I./Source/ThirdParty/ANGLE/include/GLSLANG -I./Source/WebCore -I./Source/WebCore/accessibility -I./Source/WebCore/bindings -I./Source/WebCore/bindings/generic -I./Source/WebCore/bindings/js -I./Source/WebCore/bindings/js/specialization -I./Source/WebCore/bridge -I./Source/WebCore/bridge/c -I./Source/WebCore/bridge/jni/jsc -I./Source/WebCore/bridge/jsc -I./Source/WebCore/css -I./Source/WebCore/dom -I./Source/WebCore/dom/default -I./Source/WebCore/editing -I./Source/WebCore/fileapi -I./Source/WebCore/history -I./Source/WebCore/html -I./Source/WebCore/html/canvas -I./Source/WebCore/html/parser -I./Source/WebCore/html/shadow -I./Source/WebCore/html/track -I./Source/WebCore/inspector -I./Source/WebCore/loader -I./Source/WebCore/loader/appcache -I./Source/WebCore/loader/archive -I./Source/WebCore/loader/cache -I./Source/WebCore/loader/icon -I./Source/WebCore/mathml -I./Source/WebCore/mediastream -I./Source/WebCore/notifications -I./Source/WebCore/page -I./Source/WebCore/page/animation -I./Source/WebCore/page/scrolling -I./Source/WebCore/platform -I./Source/WebCore/platform/animation -I./Source/WebCore/platform/audio -I./Source/WebCore/platform/graphics -I./Source/WebCore/platform/graphics/filters -I./Source/WebCore/platform/graphics/filters/arm -I./Source/WebCore/platform/graphics/gpu -I./Source/WebCore/platform/graphics/opengl -I./Source/WebCore/platform/graphics/opentype -I./Source/WebCore/platform/graphics/transforms -I./Source/WebCore/platform/image-decoders -I./Source/WebCore/platform/image-decoders/bmp -I./Source/WebCore/platform/image-decoders/gif -I./Source/WebCore/platform/image-decoders/ico -I./Source/WebCore/platform/image-decoders/jpeg -I./Source/WebCore/platform/image-decoders/webp -I./Source/WebCore/platform/image-decoders/png -I./Source/WebCore/platform/leveldb -I./Source/WebCore/platform/mediastream -I./Source/WebCore/platform/mock -I./Source/WebCore/platform/network -I./Source/WebCore/platform/sql -I./Source/WebCore/platform/text -I./Source/WebCore/platform/text/transcoder -I./Source/WebCore/platform/win -I./Source/WebCore/plugins -I./Source/WebCore/plugins/win -I./Source/WebCore/rendering -I./Source/WebCore/rendering/mathml -I./Source/WebCore/rendering/style -I./Source/WebCore/rendering/svg -I./Source/WebCore/storage -I./Source/WebCore/svg -I./Source/WebCore/svg/animation -I./Source/WebCore/svg/graphics -I./Source/WebCore/svg/graphics/filters -I./Source/WebCore/svg/properties -I./Source/WebCore/testing -I./Source/WebCore/testing/js -I./Source/WebCore/webaudio -I./Source/WebCore/websockets -I./Source/WebCore/workers -I./Source/WebCore/xml -I./Source/WebCore/xml/parser -I./WebCore/bindings/js -I./DerivedSources/WebCore -I./DerivedSources -I./DerivedSources/JavaScriptCore -DDATA_DIR=\"/opt/local/share\" -DENABLE_CHANNEL_MESSAGING=1 -DENABLE_METER_TAG=1 -DENABLE_PROGRESS_TAG=1 -DENABLE_JAVASCRIPT_DEBUGGER=1 -DENABLE_GAMEPAD=0 -DENABLE_SQL_DATABASE=1 -DENABLE_DATALIST=1 -DENABLE_DIRECTORY_UPLOAD=0 -DENABLE_MUTATION_OBSERVERS=1 -DENABLE_TOUCH_ICON_LOADING=0 -DENABLE_INPUT_COLOR=0 -DENABLE_INPUT_SPEECH=0 -DENABLE_ICONDATABASE=1 -DENABLE_VIDEO=1 -DENABLE_MEDIA_SOURCE=0 -DENABLE_MEDIA_STATISTICS=1 -DENABLE_FULLSCREEN_API=1 -DENABLE_VIDEO_TRACK=1 -DENABLE_MEDIA_STREAM=1 -DENABLE_XSLT=1 -DENABLE_WORKERS=1 -DENABLE_SHADOW_DOM=1 -DENABLE_SHARED_WORKERS=1 -DENABLE_FILTERS=1 -DENABLE_GEOLOCATION=1 -DENABLE_CLIENT_BASED_GEOLOCATION=1 -DENABLE_MATHML=1 -DENABLE_SVG=1 -DENABLE_SVG_FONTS=1 -DENABLE_WEB_SOCKETS=1 -DENABLE_BLOB=1 -DENABLE_REQUEST_ANIMATION_FRAME=1 -DENABLE_WEBGL=1 -DENABLE_MHTML=1 -I./Source/WebCore/loader/archive/mhtml -DENABLE_MICRODATA=1 -DWEBKITGTK_API_VERSION_STRING=\"1.0\" -DWTF_USE_SOUP=1 -I./Source/WebCore/accessibility/gtk -I./Source/WebCore/loader/gtk -I./Source/WebCore/page/gtk -I./Source/WebCore/platform/cairo -I./Source/WebCore/platform/audio/gstreamer -I./Source/WebCore/platform/graphics/cairo -I./Source/WebCore/platform/graphics/glx -I./Source/WebCore/platform/graphics/gstreamer -I./Source/WebCore/platform/graphics/gtk -I./Source/WebCore/platform/gtk -I./Source/WebCore/platform/network/soup -DWTF_USE_PANGO=1 -I./Source/WebCore/platform/graphics/pango -I./Source -I./Source/JavaScriptCore -I./Source/JavaScriptCore/API -I./Source/JavaScriptCore/assembler -I./Source/JavaScriptCore/bytecode -I./Source/JavaScriptCore/bytecompiler -I./Source/JavaScriptCore/dfg -I./Source/JavaScriptCore/heap -I./Source/JavaScriptCore/debugger -I./Source/JavaScriptCore/ForwardingHeaders -I./Source/JavaScriptCore/interpreter -I./Source/JavaScriptCore/jit -I./Source/JavaScriptCore/jit -I./Source/JavaScriptCore/parser -I./Source/JavaScriptCore/profiler -I./Source/JavaScriptCore/runtime -I./Source/JavaScriptCore/tools -I./Source/JavaScriptCore/wtf -I./Source/JavaScriptCore/wtf -I./Source/JavaScriptCore/wtf/gobject -I./Source/JavaScriptCore/wtf/gtk -I./Source/JavaScriptCore/wtf/text -I./Source/JavaScriptCore/wtf/unicode -I./Source/JavaScriptCore/yarr -I./DerivedSources/JavaScriptCore -I./Source/WTF -fno-strict-aliasing -I/opt/local/include/cairo -I/opt/local/include/glib-2.0 -I/opt/local/lib/glib-2.0/include -I/opt/local/include -I/opt/local/include/pixman-1 -I/opt/local/include/freetype2 -I/opt/local/include/libpng15 -D_REENTRANT -I/opt/local/include/enchant -I/opt/local/include/glib-2.0 -I/opt/local/lib/glib-2.0/include -I/opt/local/include -I/opt/local/include -I/opt/local/include/dbus-1.0 -I/opt/local/include/libxml2 -I/opt/local/lib/dbus-1.0/include -I/opt/local/include/glib-2.0 -I/opt/local/lib/glib-2.0/include -D_REENTRANT -I/opt/local/include/glib-2.0 -I/opt/local/lib/glib-2.0/include -I/opt/local/include -D_REENTRANT -I/opt/local/include/gstreamer-0.10 -I/opt/local/include/glib-2.0 -I/opt/local/lib/glib-2.0/include -I/opt/local/include -I/opt/local/include/libxml2 -D_REENTRANT -I/opt/local/include/libsoup-2.4 -I/opt/local/include/libxml2 -I/opt/local/include/glib-2.0 -I/opt/local/lib/glib-2.0/include -I/opt/local/include -I/opt/local/include/libxml2 -I/opt/local/include -I/opt/local/include/libxml2 -D_REENTRANT -I/opt/local/include/pango-1.0 -I/opt/local/include/glib-2.0 -I/opt/local/lib/glib-2.0/include -I/opt/local/include -I/opt/local/include/freetype2 -I/opt/local/include -I/opt/local/include -I/opt/local/include -I/opt/local/include -fvisibility-inlines-hidden -fno-rtti -pipe -O2 -arch ppc -O2 -MT Source/WebCore/platform/libWebCore_la-Length.lo -MD -MP -MF Source/WebCore/platform/.deps/libWebCore_la-Length.Tpo -c Source/WebCore/platform/Length.cpp  -fno-common -DPIC -o Source/WebCore/platform/.libs/libWebCore_la-Length.o
Source/WebCore/platform/Length.cpp:156: error: size of array 'dummylength_should_stay_small' is negative
make[1]: *** [Source/WebCore/platform/libWebCore_la-Length.lo] Error 1
make: *** [all] Error 2

[Jeremy Huddleston Sequoia]

Created attachment 162550 [details]
preprocessed source

[Jeremy Huddleston Sequoia]

sizeof(WebCore::Length) is 16
sizeof(WebCore::SameSizeAsLength) is 8

[Jeremy Huddleston Sequoia]

Yeah, I don't know why that assert should be there.  It's clear that it is not the case.  The assert is essentially saying that these two structures should take up the same amount of memory, and that's clearly not the case:

struct Length {
    union {
        int m_intValue;
        float m_floatValue;
    };
    bool m_quirk;
    unsigned char m_type;
    bool m_isFloat;
};

struct SameSizeAsLength {
    int32_t value;
    int32_t metaData;
};

[Jeremy Huddleston Sequoia]

Or rather, it makes assumptions about packing and sizes that aren't always true...

[Alexey Proskuryakov]

This assertion should pass for any port that doesn't want to waste memory on lengths, so the right fix would be to correct Length structure definition. 

This does not imply that we would necessarily accept a patch for PowerPC alone.

[Simon Fraser (smfr)]

No plans to make PPC build.