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Windows Kernel Mode

All files accessed by BullseyeCoverage at run-time are located on the target system in %DriverData%\BullseyeCoverage, or if that directory does not exist, %SystemDrive%\BullseyeCoverage. Locating files in %DriverData%\BullseyeCoverage complies with driver package isolation requirements.

Create the %DriverData%\BullseyeCoverage directory at the command prompt in administrator mode:

C:\>mkdir %DriverData%\BullseyeCoverage

Copy the coverage file from the host system to this directory whenever you install your driver.

C:\>copy …\test.cov %DriverData%\BullseyeCoverage\test.cov

After testing your kernel code, you can merge the results back with this command:

covmerge -f …\test.cov %DriverData%\BullseyeCoverage\test.cov

The BullseyeCoverage run-time searches for environment variables in the file %DriverData%\BullseyeCoverage\env.txt, if it exists. This ASCII file has the format below.

name1=value1
name2=value2
…

Filenames are relative to the %DriverData%\BullseyeCoverage directory. For example, COVFILE=dir/test.cov means %DriverData%\BullseyeCoverage\dir\test.cov. Do not specify an absolute path for any filename.

The default value for COVFILE is test.cov which means %DriverData%\BullseyeCoverage\test.cov.

Run-time error messages are normally displayed in the host debugger Command window (using the kernel mode support routine DbgPrintEx). If no debugger is connected and environment variable COVERR is unset, run-time error messages are lost.

Your entry point function name must end with DriverEntry. For example, DriverEntry, FxDriverEntry, or GsDriverEntry.

Native Mode

Native mode drivers may run before the \DriverData symbolic link is established. Therefore, if files cannot be found as described above, the run-time looks for them relative to the root directory of the first volume found by checking each partition \Device\Harddisk0\PartitionN, where N is 1 to 9.

Export Drivers

For an export driver, you must add a call to the BullseyeCoverage run-time function cov_term in your DllUnload function. For example:

void __cdecl cov_term(void);
NTSTATUS DllUnload()
{
    #if _BullseyeCoverage
        cov_term();
    #endif
    return STATUS_SUCCESS;
}

Updated: 12 Aug 2025

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