On Tue, 31 May 2022 23:39:09 GMT, Nikita Gubarkov <d...@openjdk.java.net> wrote:
> `CTFontCopyAvailableTables` can return null, which causes subsequent call to
> `CFArrayGetCount` to crash with SEGFAULT, just added a null-check.
Sorry for the confusion, "maxp" being absent was only my assumption:
`CTFontCopyTable` returned NULL for it, but I cannot be 100% sure about what's
going on here, given that `CTFontCopyAvailableTables` doesn't even return
anything.
BTW I see that `CTFontCopyAvailableTables` return type is marked as nullable,
though conditions when it can be null are not specified.
So this is a very old font and I couldn't even find a tool which could edit it
or at least parse and see what's inside, CoreText API is not very helpful as
well. But the thing is: we can actually render this font, problems begins when
we try to do a full layout, so in my opinion, adding this null-check is okay,
we're just not doing anything useful in our layout code instead of crashing :).
And also if I'm not missing something, my change doesn't affect any behavior
other that fixing the crash, look:
1. When I debugged it, I found around 5 or something calls to
`getTableBytesNative` where it could crash, but the only table required by spec
was "maxp" - I assume when asking for non-required table, callers already
handle NULL case.
2. Caller uses "maxp" table to calculate upem (and falls back to 1000 if
there's no such table) and set font scale (libharfbuzz/hb-font.cc:1512):
font->x_scale = font->y_scale = hb_face_get_upem (face);
3. But this scale is then overwritten anyway, so it doesn't even matter that we
didn't find "maxp" table at all (libfontmanager/hb-jdk-font.cc:410):
hb_font_set_scale (font,
HBFloatToFixed(jdkFontInfo->ptSize*jdkFontInfo->devScale),
HBFloatToFixed(jdkFontInfo->ptSize*jdkFontInfo->devScale));
So it looks like there's really no behavior changed other than not crashing. In
my tests text is properly rendered with `Font.layoutGlyphVector` being visually
identical to `Font.createGlyphVector`.
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PR: https://git.openjdk.java.net/jdk/pull/8962
