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Re: crash when using local display but not remote

From: Sergii Stoian
Subject: Re: crash when using local display but not remote
Date: Tue, 4 Feb 2020 23:15:59 +0200

On Feb 4, 2020, at 20:43, Fred Kiefer <address@hidden> wrote:

Am 04.02.2020 um 11:21 schrieb Sergii Stoian <address@hidden>:

On Mon, Feb 3, 2020 at 8:59 AM Fred Kiefer <address@hidden> wrote:

Am 03.02.2020 um 00:53 schrieb Sergii Stoian <address@hidden>:

On Mon, Feb 3, 2020 at 1:05 AM Fred Kiefer <address@hidden> wrote:

I just ran a quick scan with valgrind and this did not detect any obvious wrong memory access. Looking at the code once again I see that line 4276 may be wrong for certain bytesPerRow values. Here the old code that copied over line by line is safer. Maybe we could check bytesPerRow versus pixelsWide*4 and use the old code if they are not the same?

Line 4276 looks like this: "xcursorImage->yhot = hotp.y;" Do you mean memcpy call at 4279?

Yes, it was line 4276 in the original merge commit, but has changed since then.

Could you please explain why old code is safer?

Old code:
for (row = 0; row < h; row++)
   memcpy((char*)xcursorImage->pixels + (row * (w * 4)),
          data + (row * bytesPerRow),

New code:

memcpy((char*)xcursorImage->pixels, data, w * h * colors);

In general it is safer as the new code expects that the image is fully packed. (You moved the comment with the conversion from unpacked to packed over to the swap function) If bytesPerRow is not equal to w * 4 (there may be a few extra bytes to align stuff a bit), then the new code would not transfer the correct data.  We would end up with random garbage in between. But in this special case the image comes from GSStandardImage and at least for the case where there are alpha values that function should already return a packed image. Thinking about it the old code should only have copied w * 4 bytes for each row. The old code could have written a few bytes past the pixels array.

Clear explanation, thank you. It is a usual case when image contains more bytes than image size (width * height)?
I feel we need to return back old code with your explanation in comment.
What do you think?


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