From 5683a8568adc9c13c1cf9d360dae105dc60b145d Mon Sep 17 00:00:00 2001 From: Dean Deng Date: Tue, 25 Aug 2020 16:26:53 -0700 Subject: Expose basic coverage information to userspace through kcov interface. In Linux, a kernel configuration is set that compiles the kernel with a custom function that is called at the beginning of every basic block, which updates the memory-mapped coverage information. The Go coverage tool does not allow us to inject arbitrary instructions into basic blocks, but it does provide data that we can convert to a kcov-like format and transfer them to userspace through a memory mapping. Note that this is not a strict implementation of kcov, which is especially tricky to do because we do not have the same coverage tools available in Go that that are available for the actual Linux kernel. In Linux, a kernel configuration is set that compiles the kernel with a custom function that is called at the beginning of every basic block to write program counters to the kcov memory mapping. In Go, however, coverage tools only give us a count of basic blocks as they are executed. Every time we return to userspace, we collect the coverage information and write out PCs for each block that was executed, providing userspace with the illusion that the kcov data is always up to date. For convenience, we also generate a unique synthetic PC for each block instead of using actual PCs. Finally, we do not provide thread-specific coverage data (each kcov instance only contains PCs executed by the thread owning it); instead, we will supply data for any file specified by -- instrumentation_filter. Also, fix issue in nogo that was causing pkg/coverage:coverage_nogo compilation to fail. PiperOrigin-RevId: 328426526 --- pkg/abi/linux/ioctl.go | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) (limited to 'pkg/abi/linux') diff --git a/pkg/abi/linux/ioctl.go b/pkg/abi/linux/ioctl.go index 2c5e56ae5..d6dbedc3e 100644 --- a/pkg/abi/linux/ioctl.go +++ b/pkg/abi/linux/ioctl.go @@ -117,3 +117,24 @@ const ( func IOC(dir, typ, nr, size uint32) uint32 { return uint32(dir)<<_IOC_DIRSHIFT | typ<<_IOC_TYPESHIFT | nr<<_IOC_NRSHIFT | size<<_IOC_SIZESHIFT } + +// Kcov ioctls from kernel/kcov.h. +var ( + KCOV_INIT_TRACE = IOC(_IOC_READ, 'c', 1, 8) + KCOV_ENABLE = IOC(_IOC_NONE, 'c', 100, 0) + KCOV_DISABLE = IOC(_IOC_NONE, 'c', 101, 0) +) + +// Kcov trace types from kernel/kcov.h. +const ( + KCOV_TRACE_PC = 0 + KCOV_TRACE_CMP = 1 +) + +// Kcov state constants from kernel/kcov.h. +const ( + KCOV_MODE_DISABLED = 0 + KCOV_MODE_INIT = 1 + KCOV_MODE_TRACE_PC = 2 + KCOV_MODE_TRACE_CMP = 3 +) -- cgit v1.2.3