[webkit-dev] CSS Parse error in <link rel> element.

Thu Feb 9 04:09:37 PST 2017

Finally I zeroed in on 3 "calc" candidates from the stylesheet which are
causing the CSS parser to fail:

height:calc(100vh - 200px)
height:calc(100vh - 230px)
max-height:calc(100vh - 200px)

I think it is the very first one and the remaining two never get processed.

I put in some debug statements in the code and the corresponding output for
this is:

ATUL: value->id = 0 propId = 1080
ATUL: in CSSPropertyHeight
ATUL: in CSSPropertyWebkitLogicalHeight
ATUL: in CSSCalcValue::create
ATUL: in parseValueExpression, calling parseAdditiveValueExpression
ATUL: calling CSSCalcBinaryOperation::create from
parseAdditiveValueExpression
ATUL: operatorCharacter = -
ATUL: lhs = 1 rhs = 1
ATUL: leftSide category = ATUL: m_category = 5
5
ATUL: rightSide category = ATUL: m_category = 1
1
ATUL: m_category = 5
ASSERTION FAILED: leftSide->category() != CalcOther &&
rightSide->category() != CalcOther
css/CSSCalculationValue.cpp(293) : static
WTF::PassRefPtr<WebCore::CSSCalcBinaryOperation>
WebCore::CSSCalcBinaryOperation::create(WTF::PassRefPtr<WebCore::CSSCalcExpressionNode>,
WTF::PassRefPtr<WebCore::CSSCalcExpressionNode>, WebCore::CalcOperator)
1   0x12e8a80c bin/phantomjs() [0x12e8a80c]
< stack trace removed >

So the question is, is the calc expression valid one?

Best regards,
Atul.

On Thu, Feb 9, 2017 at 2:17 PM, Atul Sowani <sowani at gmail.com> wrote:

> @Konstantin thanks for the suggestions. I disabled CSS JIT on x85 but
> there was no negative impact on the results on x86. So I guess the issue is
> a genuine ppc64le problem. I have picked up the starting points mentioned
> in this thread earlier and debugging the issue. I have also isolated the
> issue to a single CSS file which is causing the problem. Now I am trying to
> isolate the exact entry in the CSS file which is causing the trouble.
>
> Thanks!
> Atul.
>
> On Tue, Feb 7, 2017 at 3:53 PM, Konstantin Tokarev <annulen at yandex.ru>
> wrote:
>
>>
>>
>> 07.02.2017, 12:55, "Atul Sowani" <sowani at gmail.com>:
>> > Thanks Geoffrey, Alex, Yoav for the debugging pointer. I am debugging
>> the issue further using this information and will most likely need some
>> more help in immediate future as well.
>> >
>> > Unfortunately, I don't have a stand-alone test case which can be tested
>> with qtwebkit. I am trying to load a page using PhantomJS and it's
>> crashing. The typical URLs which cause it to crash are
>> http://engadget.com and http://cnn.com - both of these load without any
>> issue on x86 platform though, so the issue seems to be specific to ppc64le.
>>
>> A few suggestions:
>>
>> 1. I suppose you are building with disabled JIT, as WebKit does not
>> implement JIT for any PPC variant in official tree. This may introduce
>> subtle differences in behavior, for example I once encountered layout test
>> that was failing only when CSS JIT was disabled. You can try building
>> without JIT on x86_64 and compare.
>>
>> 2. It might be miscompilation, as your platform may not be as thoroughly
>> tested as more mainstream ones. You can try to build with -O0, -O1, -O2
>> (default is -O3). Alternatively, try building with different compiler (at
>> least GCC and Clang support ppc64le and are fine for WebKit, xlC may not
>> work though), or try different version of your compiler.
>>
>> 3. Note that webkit-qt list is more appropriate for issues specific for
>> QtWebKit. Make sure you are using latest release (technology preview 5 at
>> the moment [1])
>>
>> [1] https://github.com/annulen/webkit/releases/tag/qtwebkit-tp5
>>
>> >
>> > Thanks,
>> > Atul.
>> >
>> > On Mon, Feb 6, 2017 at 5:56 PM, Yoav Weiss <yoav at yoav.ws> wrote:
>> >> Hi Atul,
>> >>
>> >> I second Alex's suggestion (perhaps followed by
>> HTMLLinkElement::process() and other places in that file that refer to
>> `hrefAttr`).
>> >> If you have a test case online, I could try to take a look and maybe
>> provide more guidance.
>> >>
>> >> Cheers :)
>> >> Yoav
>> >>
>> >> On Fri, Feb 3, 2017 at 9:19 PM Alex Christensen <
>> achristensen at apple.com> wrote:
>> >>> I would start looking at HTMLLinkElement::parseAttribute.
>> >>> LinkHeader.cpp contains parsers for link headers, which are related.
>> Yoav knows more about those.  Those parsers ought to be united more.
>> >>>
>> >>>> On Feb 3, 2017, at 1:17 AM, Atul Sowani <sowani at gmail.com> wrote:
>> >>>> At present I am focusing on CSSParser::findURI() particularly
>> and CSSParser::realLex() other related functionality in CSSParser.cpp
>> - hope I am on right track. ;-)
>> >>>>
>> >>>> Please let me know if I should be looking at some other
>> functionality as well to resolve this issue.
>> >>>>
>> >>>> Thanks!
>> >>>> Atul.
>> >>>>
>> >>>> On Fri, Feb 3, 2017 at 2:33 PM, Atul Sowani <sowani at gmail.com>
>> wrote:
>> >>>>> Hi,
>> >>>>>
>> >>>>> I came across an issue in qtwebkit CSS parser while working on a
>> PhantomJS crash. The issue seems to be with parsing of <link rel="..."
>> href="..."> type elements in an HTML page. What I observed is that the
>> parser is trying to interpret the value for href given inside
>> double-quotes. The value contains a "-" (e.g. "
>> http://some.domain.com/some-page-etc-etc"). The "-" sign is being
>> interpreted as minus and then things go wrong. In another case I found that
>> "\g" embedded in the value (e.g. "http://some.domain.com/some-p
>> age/global/something") is also creating issues. In essence, the parser
>> is trying to interpret the value, which I believe, it should not.
>> >>>>>
>> >>>>> I am willing to dive further into it to debug and fix the issue,
>> but looking at the complexity and size of WebCore, I think I would benefit
>> a lot to expedite a fix, if I could get some tips about which code
>> area/functionality I should specifically focus in the WebCore. Looking
>> forward to some help in this regard.
>> >>>>>
>> >>>>> Thanks,
>> >>>>> Atul.
>> >>>> _______________________________________________
>> >>>> webkit-dev mailing list
>> >>>> webkit-dev at lists.webkit.org
>> >>>> https://lists.webkit.org/mailman/listinfo/webkit-dev
>> > ,
>> >
>> > _______________________________________________
>> > webkit-dev mailing list
>> > webkit-dev at lists.webkit.org
>> > https://lists.webkit.org/mailman/listinfo/webkit-dev
>>
>>
>> --
>> Regards,
>> Konstantin
>>
>
>
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