MALLOC_CHECK_=0 ./awimage img.dump

[UMLAUTaxl]

With a freshly unpacked, not modified image I received as follows:

*** glibc detected *** ./awimage: double free or corruption (!prev): 0x0000000000bbc250 ***

After

export MALLOC_CHECK_=0

it works fine and puts out a file the same size as original. Haven't flashed so not sure.
If you're interested I compiled awimage with -g again and could post the gdb and other output ...

[TheSeven]

This is a duplicate fclose of the packing config file. One is inside the parser, one in the function calling it, that also opens the file. Comment either one of them and that problem will go away.