File format

gcda/gcno structure (Input of lcov-rs)

These are binary files. Reference

gcda and gcno files follow the same "container" format:

Offset	Size (bytes)	Purpose	Ignored?
0	4	Magic String ("gcda" or "gcno")
4	4	Version
8	4	Stamp (used for "merging")	x
12	*	Contains records

Each file is contained with different types of records.

gcno records

TAG_FUNCTION[0x01000000]

Offset	Size (bytes)	Purpose	Ignored?
0	4	Identifier
4	4	Line # Checksum
8	4	Config Checksum
12	4	Fn Name Length
16	^	Fn Name
?	4	Source Path Length
?	^	Source Path
?	4	Line #

TAG_LINES[0x01450000]

Some exceptions, see gcov header

Offset	Size (bytes)	Purpose	Ignored?
0	4	Block #	x
4	?	Contains multiple lines

Where each line is:

Offset	Size (bytes)	Purpose	Ignored?
0	4	Line #
------	------	If Line # == 0, then changing file:	------
4	4	Next filename's length
8	^	Next filename

TAG_END_FILE[0x00000000]

If this record is encountered, then the rest of the file can be ignored.

gcda records

TAG_PROGRAM_SUMMARY[0xa3000000]

Offset	Size (bytes)	Purpose	Ignored?
0	4	Number of counters	?
4	4	Number of program runs	?
8	8	Sum of all counters accumulated	?
16	8	Maximum value in single run	?
24	8	Sum of all runs' maximums	?
32	?	Histogram of counter values	?

TAG_FUNCTION[0x01000000]

Note: if this record isn't 3 bytes, it should be ignored.

Offset	Size (bytes)	Purpose	Ignored?
0	4	Identifier
4	4	Line # Checksum
8	4	Config Checksum

TAG_COUNTER_BASE[0x01a10000]

Curiously unused when gcov reads gcda files. When in the main parse loop, the closest is a GCOV_TAG_FOR_COUNTER check, (which is based off of TAG_COUNTER_BASE)

TAG_END_FILE[0x00000000]

If this record is encountered, then the rest of the file can be ignored.

lcov "info" file (Output of lcov-rs)

This is a text file. Reference

Prefix	Purpose	Data Format	Strategy
TN	Test Name	String name of test	Leave blank, like lcov is doing in local tests
SF	Source File	Absolute path to source file	Get function identifiers from gcda, use it to reference function definition in gcno file. Print the function's source file
FN	Function	line # of fn start, fn name	Same as above, but print function definition's name
FNDA	Fn Data	Execution count of fn, fn name	?
FNF	# Fn Found	integer	Print number of TAG_FUNCTION encountered in gcda
FNH	# Fn Executed	integer	?
DA	Executions for some Line	line #, execution count	?
LF	# Lines Found	integer	Count lines from gcno lines records
LH	# Lines Executed	integer	?
end_of_record	End of Record	Signifies end of data for source file	Use the constant "end_of_record"