This is a variation on kernel module support for the companion FPVM project, which is why "fpvm" appears in this subdirectory. The majority of changes are in how the interrupt return process works, and the code for that is in fpspy itself, in particular fpspy/src/x64/user_fpspy_entry.S

As with all kernel modules, this requires root to install, and it can be sensitive to particular kernel versions. We test on an AMD EPYC 7443P 24-Core Processor with kernel 5.15.0-134-generic on Ubuntu 22.04.4. LTS.

./kmod_build.sh

If successful, this will leave you with fpvm-kmod/fpvm-dev.ko

sudo ./kmod_setup.sh

If successful, an lsmod will show fpvm-dev as an available module. Inserting this module is more complicated than a simple insmod because we must make it aware of various symbols in the core kernel that are a challenge to discover within the module itself.

To use with FPSpy, you must enable the Trap Short Circuiting feature using make menuconfig and then rebuild FPSpy. It is safe to enable this feature even if the kernel module is not available, since FPSpy will fall back on regular SIGFPE signaling if it cannot communicate with the kernel module.

The subdirectory signal_latency contains code for measuring floating point trap costs when delivered using SIGFPE and via the kernel module.