To generate a call graph:


1. Fetch, build, and install the 'egypt' Perl package from:

    http://www.gson.org/egypt/

  wget http://www.gson.org/egypt/download/egypt-1.10.tar.gz
  tar -xf egypt-1.10.tar.gz
  cd egypt-1.10/
  perl Makefile.PL
  make
  sudo make install

Program is installed to /usr/local/bin/egypt

2. Install GraphViz

  sudo apt install graphviz

3. Modify the target source's Makefile to include the gcc option:

   -fdump-rtl-expand

In the Linux source-tree this can be done on a per-directory basis to target subsystems. E.g. for ecryptfs:

diff --git a/fs/ecryptfs/Makefile b/fs/ecryptfs/Makefile
index 49678a6..f28fd7b 100644
--- a/fs/ecryptfs/Makefile
+++ b/fs/ecryptfs/Makefile
@@ -1,7 +1,7 @@
 #
 # Makefile for the Linux eCryptfs
 #
+ccflags-y += -fdump-rtl-expand
 obj-$(CONFIG_ECRYPT_FS) += ecryptfs.o
 
 ecryptfs-y := dentry.o file.o inode.o main.o super.o mmap.o read_write.o \

4. (Re)build the kernel

  make O=../builds/amd64/ bzImage

 which will generate .expand files where-ever the gcc flag is used

  ls fs/ecryptfs/*.expand

crypto.c.192r.expand  dentry.c.192r.expand  inode.c.192r.expand     kthread.c.192r.expand  messaging.c.192r.expand  mmap.c.192r.expand        super.c.192r.expand
debug.c.192r.expand   file.c.192r.expand    keystore.c.192r.expand  main.c.192r.expand     miscdev.c.192r.expand    read_write.c.192r.expand

5. Generate the structured data and pass it through graphviz to generate a directed graph in SVG

  egypt *.expand | dot -Grankdir=LR -Tsvg -o ecryptfs_callgraph.svg