[Ffmpeg-devel] [PATCH]: Too much alignment assumed by H264 decoder

David S. Miller davem
Thu Dec 22 19:21:47 CET 2005

From: Mike Melanson <mike at multimedia.cx>
Date: Thu, 22 Dec 2005 08:44:58 -0800

> 	Wait... run that by me again: 8-byte alignment causes crashes but 
> 4-byte alignment is okay? I hope I don't have to point out that this 
> doesn't make much sense. Or are you saying that the compiler you are 
> using on Sparc does not support 8-byte alignment and so the data 
> structure is being aligned on a random boundary?

It's 4-byte aligned.  The compiler emits ldd and std instructions for
the uint64_t loads and stores and this gets an unaligned trap which
kills the program.

Both mvd_table and motion_val are declared like this:

    int16_t     (*mvd_table[2])[2];
    int16_t (*motion_val[2])[2];\

what is there to ensure the necessary 8-byte alignment?

I even see assignments of the form:

	pic->motion_val[i]= pic->motion_val_base[i]+4

so how can it ever be assumed to be any more than 4-byte

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