misc: add lcov scripts, README.md

See extras/lcov

Type: feature

Signed-off-by: Dave Barach <dave@barachs.net>
Change-Id: Id229436bd94cd18bcd0f3a3d938eae2b28d5b1f5

extras/lcov/README.md

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+## Prerequisites
+
+The Linux gcov and lcov tools are fussy about gcc / g++ compiler
+versions. As of this writing, Ubuntu 18.04 gcov / lcov work with
+these toolchain versions:
+
+  $ gcc --version
+  gcc (Ubuntu 7.4.0-1ubuntu1~18.04.1) 7.4.0
+  $ g++ --version
+  g++ (Ubuntu 8.3.0-6ubuntu1~18.04.1) 8.3.0
+
+Refer to
+https://askubuntu.com/questions/26498/how-to-choose-the-default-gcc-and-g-version for information on how to install multiple gcc / g++ versions, and
+switch between them.
+
+You'll need to install the following additional packages:
+
+  $ sudo apt-get install gcovr ggcov lcov
+
+## Compile an instrumented vpp image
+
+Two ways:
+
+  $ cd <workspace-root>
+  $ make test-gcov
+  $ ## interrupt compilation after building the image
+
+or
+  $ cd <workspace-root>/build-root
+  $ make PLATFORM=vpp TAG=vpp_gcov vpp-install
+
+## Initialize the lcov database
+
+  $ cd <workspace-root>
+  $ ./extras/lcov/lcov_prep
+  $ make test-gcov or make TEST=my_test test-gcov
+  $ # repeat or vary as desired to increase reported coverage
+  $ # Generate the report:
+  $ ./extras/lcov/lcov_post
+
+You can run vpp manually, do anything you like. Results are cumulative
+until you re-run the "prep" script.
+
+## Look at the results
+
+Point a browser at file:///<workspace-root>/build-root/html/index.html

extras/lcov/lcov_post

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+#!/bin/bash
+
+set -e
+
+cd build-root
+rm -rf html
+mkdir html
+lcov --no-checksum --directory . --capture --output-file out.info
+genhtml out.info -o html

extras/lcov/lcov_prep

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+#!/bin/bash
+
+set -e
+
+cd build-root
+rm -rf html
+lcov --capture --initial --directory . --output-file lcov.out