From 2b0c34c8d13ab4a899a722ae272a366bf6051168 Mon Sep 17 00:00:00 2001
From: Johannes Stoelp <johannes.stoelp@gmail.com>
Date: Wed, 17 May 2023 18:44:37 +0200
Subject: gcov: example to generate coverage

---
 src/SUMMARY.md                |  1 +
 src/development/README.md     |  1 +
 src/development/gcov.md       | 60 +++++++++++++++++++++++++++++++++++++++++++
 src/development/gcov/Makefile | 24 +++++++++++++++++
 src/development/gcov/cov.cc   | 17 ++++++++++++
 5 files changed, 103 insertions(+)
 create mode 100644 src/development/gcov.md
 create mode 100644 src/development/gcov/Makefile
 create mode 100644 src/development/gcov/cov.cc

(limited to 'src')

diff --git a/src/SUMMARY.md b/src/SUMMARY.md
index f0c9984..ae7bc1e 100644
--- a/src/SUMMARY.md
+++ b/src/SUMMARY.md
@@ -49,6 +49,7 @@
     - [ld.so](./development/ld.so.md)
     - [symbol versioning](./development/symbolver.md)
     - [python](./development/python.md)
+    - [gcov](./development/gcov.md)
 
 - [Linux](./linux/README.md)
     - [systemd](./linux/systemd.md)
diff --git a/src/development/README.md b/src/development/README.md
index bbd27a2..dfea5cd 100644
--- a/src/development/README.md
+++ b/src/development/README.md
@@ -8,3 +8,4 @@
 - [ld.so](./ld.so.md)
 - [symbol versioning](./symbolver.md)
 - [python](./python.md)
+- [gcov](./gcov.md)
diff --git a/src/development/gcov.md b/src/development/gcov.md
new file mode 100644
index 0000000..c97a1b0
--- /dev/null
+++ b/src/development/gcov.md
@@ -0,0 +1,60 @@
+# gcov(1)
+
+Generate code coverage reports in text format.
+
+Compile the source files of interest and link the final binary with the
+following flags:
+- `-fprofile-arcs` instruments the generated code such that it writes a `.gcda`
+  file when being executed with details about which branches are taken
+- `-ftest-coverage` writes a `.gcno` notes file which is used by `gcov` during
+  generation of the coverage report
+
+Depending on the build environment one may also set `-fprofile-abs-path` to
+generate absolute path names into the `.gcno` note files, this can ease setups
+where compilations are done in different directories to the source directory.
+
+> `gcc` / `clang` also support an alias flag `--coverage` which during
+> compilation time is equivalent to `-fprofile-arcs -ftest-coverage` and during
+> link time `-lgcov`.
+
+After running the instrumented binary, the human readable report can then be
+generated for a single file for example such as
+```shell
+gcov <SRC FILE | OBJ FILE>
+```
+
+## Example
+```cpp
+{{#include gcov/cov.cc:3:}}
+```
+
+The `gcov` coverage report can be generated as follows for `gcc` or `clang`.
+```make
+{{#include gcov/Makefile:3:}}
+```
+
+The will generate a report similar to the following.
+```text
+cat cov.cc.gcov
+        -:    0:Source:cov.cc
+        -:    0:Graph:cov.gcno
+        -:    0:Data:cov.gcda
+        -:    0:Runs:1
+        -:    1:// Copyright (C) 2023 johannst
+        -:    2:
+        -:    3:#include <cstdio>
+        -:    4:
+        2:    5:void tell_me(int desc) {
+        2:    6:  if (desc & 1) {
+        2:    7:    std::puts("this");
+        -:    8:  } else {
+    #####:    9:    std::puts("that");
+        -:   10:  }
+        2:   11:}
+        -:   12:
+        1:   13:int main(int argc, char *argv[]) {
+        1:   14:  tell_me(argc);
+        1:   15:  tell_me(argc);
+        1:   16:  return 0;
+        -:   17:}
+```
diff --git a/src/development/gcov/Makefile b/src/development/gcov/Makefile
new file mode 100644
index 0000000..f27f8d8
--- /dev/null
+++ b/src/development/gcov/Makefile
@@ -0,0 +1,24 @@
+# Copyright (C) 2023 johannst
+
+CXXFLAGS = -fprofile-arcs -ftest-coverage
+# or the alias
+#CXXFLAGS = --coverage
+
+cov-gcc: clean
+	g++ $(CXXFLAGS) -c -o cov.o cov.cc
+	g++ $(CXXFLAGS) -o $@ cov.o
+	./$@
+	gcov --demangled-names cov.cc
+	cat cov.cc.gcov
+.PHONY: cov-gcc
+
+cov-clang: clean
+	clang++ $(CXXFLAGS) -c -o cov.o cov.cc
+	clang++ $(CXXFLAGS) -o $@ cov.o
+	./$@
+	llvm-cov gcov --demangled-names cov.cc
+	cat cov.cc.gcov
+.PHONY: cov-clang
+
+clean:
+	$(RM) *.gcov *.gcno *.gcda *.o cov-*
diff --git a/src/development/gcov/cov.cc b/src/development/gcov/cov.cc
new file mode 100644
index 0000000..3737d81
--- /dev/null
+++ b/src/development/gcov/cov.cc
@@ -0,0 +1,17 @@
+// Copyright (C) 2023 johannst
+
+#include <cstdio>
+
+void tell_me(int desc) {
+  if (desc & 1) {
+    std::puts("this");
+  } else {
+    std::puts("that");
+  }
+}
+
+int main(int argc, char *argv[]) {
+  tell_me(argc);
+  tell_me(argc);
+  return 0;
+}
-- 
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