[lld] r308809 - Don't crash on an empty section with an ALIGN.

[George Rimar via llvm-commits]

>>Please note that this is a completely different kind of work compared
>>to what we did last year.
>>In fact, while in the linker input case you can just "tolerate"
>>crashes, because the output of the compiler is the input to the linker
>>(garbage-in garbage-out), here you have human input (i.e. the linker
>>script tests).
>>We could try to never crash on invalid linker scripts and emit a sane
>>diagnostic instead, if possible.
>>
>>Thanks,
>>
>>--
>>Davide
>
>Yeah, thats exactly what I was thinking about :)
>Honestly at previous week I tried to do quick AFL run out of curiosity
>to check what happen with current LLD. I mutated testcase objects,
>just like the year ago. After 10h run it found few crashes, but after review
>of them I found it will probably be hard to justify and land fixes.
>
>And scripts are really different at this point.
>I agree that we should never crashs/hang for them.
>
>George.

Just want to share first fuzzing results. After about 20h of total fuzzing it
found 5 unique segfaults. They are: D36145, D36140, D36138, D35942, D35891.

I am using AFL with dictionary containing different linker script commands and
constructions (https://justpaste.it/19lh3).

Input data for fuzzing is a set of linkerscripts taken from LLD testcases. 
I am using -shared and single input object which is compiled from trivial hello
world look-like app (https://justpaste.it/19lhb).

I want to let it run few more days probably to see what else can it find.
This approach is probably too dumb, but showed some useful results.

George.