The bl entry contains information about a specific basic block of object code, which is inside the function named in the surrounding fu and efu lines. It contains the data fields:
bl <source line #> <# hits>
The <source line #> gives the first line number which contributed instructions to the basic block. It is possible that other lines following this line have also contributed instructions to the basic block. Because it is possible to have multiple basic blocks on a given line, line numbers are not necessarily unique within the export file.
The <# hits> field gives the number of times that specific basic block was used in all the sessions contributing to the total for that file.