bop_printf internal buffer is too small
uts/i86pc/os/fakebop.c is using internal buffer to support bop_printf():
#define BUFFERSIZE 256
static char buffer[BUFFERSIZE];
As one debug message is reporting boot command line, the command line can get quite large due to property lists setup with -B switch, the buffer size 256 may not be big enough (I have seen this), cutting the long printout. I think 512 is safer value for buffer size and should cover the use cases better.