use the latest better Makefile template

Author: kaiwan

ch8/lowlevel_mem/Makefile

@@ -1,4 +1,13 @@
-# Makefile
+# ch5/lkm_template/Makefile
+# ***************************************************************
+# This program is part of the source code released for the book
+#  "Linux Kernel Programming" 2E
+#  (c) Author: Kaiwan N Billimoria
+#  Publisher:  Packt
+#  GitHub repository:
+#  https://github.com/PacktPublishing/Linux-Kernel-Programming_2E
+#
+# From: Ch 5 : Writing Your First Kernel Module LKMs, Part 2
 # ***************************************************************
 # Brief Description:
 # A 'better' Makefile template for Linux LKMs (Loadable Kernel Modules); besides
@@ -13,92 +22,117 @@
 # To get started, just type:
 #  make help
 #
-# For details on this so-called 'better' Makefile, please refer my book
-# 'Linux Kernel Programming' 2nd Ed, Packt, 2023, Chapter 5, section
+# For details, please refer the book, Ch 5, section
 # 'A "better" Makefile template for your kernel modules'.
+#
+# AUTHOR : Kaiwan N Billimoria
+# DESCRIPTION : A simple kernel module 'better' Makefile template
+# LICENSE : Dual MIT/GPL
+# VERSION : 0.2
 
 #------------------------------------------------------------------
-# Set FNAME_C to the kernel module name source filename (without .c)
+# IMPORTANT : Set FNAME_C to the kernel module name source filename (without .c).
 # This enables you to use this Makefile as a template; just update this variable!
 # As well, the MYDEBUG variable (see it below) can be set to 'y' or 'n' (no being
 # the default)
 FNAME_C := lowlevel_mem
 ifeq ($(FNAME_C),)
-  $(error You MUST pass the C file like this:\
-make FNAME_C=csrc-filename-without-.c target-name)
-else
-  $(info [FNAME_C = $(FNAME_C)])
+  $(error ERROR: you Must set the FNAME_C variable in the Makefile)
 endif
 #------------------------------------------------------------------
 
-# To support cross-compiling for kernel modules:
+#--- To support cross-compiling for kernel modules
 # For architecture (cpu) 'arch', invoke make as:
 #  make ARCH=<arch> CROSS_COMPILE=<cross-compiler-prefix>
+# F.e. to cross-compile for the AArch64:
+#  make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu-
+#
+# Alternately:
+#  export ARCH=<arch>
+#  export CROSS_COMPILE=<cross-compiler-prefix>
+#  make
+#
 # The KDIR var is set to a sample path below; you're expected to update it on
-# your box to the appropriate path to the kernel src tree for that arch.
+# your box to the appropriate path to the kernel source tree for that arch.
 ifeq ($(ARCH),arm)
   # *UPDATE* 'KDIR' below to point to the ARM Linux kernel source tree on your box
-  KDIR ?= ~/rpi_work/kernel_rpi/linux
+  KDIR ?= ~/arm_prj/kernel/linux
 else ifeq ($(ARCH),arm64)
   # *UPDATE* 'KDIR' below to point to the ARM64 (Aarch64) Linux kernel source
   # tree on your box
-  KDIR ?= ~/kernel/linux-5.4
+  KDIR ?= ~/arm64_prj/kernel/linux-5.10.60
 else ifeq ($(ARCH),powerpc)
   # *UPDATE* 'KDIR' below to point to the PPC64 Linux kernel source tree on your box
-  KDIR ?= ~/kernel/linux-5.0
+  KDIR ?= ~/ppc_prj/kernel/linux-5.4
 else
   # 'KDIR' is the Linux 'kernel headers' package on your host system; this is
   # usually an x86_64, but could be anything, really (f.e. building directly
   # on a Raspberry Pi implies that it's the host)
   KDIR ?= /lib/modules/$(shell uname -r)/build
 endif
+#---
 
 # Compiler
 CC     := $(CROSS_COMPILE)gcc
-#CC := clang
+#CC    := clang
+STRIP := ${CROSS_COMPILE}strip
 
 PWD            := $(shell pwd)
 obj-m          += ${FNAME_C}_lkm.o
 lowlevel_mem_lkm-objs := ${FNAME_C}.o ../../klib.o
 
 #--- Debug or production mode?
-# Set the MYDEBUG variable accordingly to y/n resp.
+# Set the MYDEBUG variable accordingly to y/n resp. We keep it off (n) by default.
 # (Actually, debug info is always going to be generated when you build the
 # module on a debug kernel, where CONFIG_DEBUG_INFO is defined, making this
-# setting of the ccflags-y (or EXTRA_CFLAGS) variable mostly redundant (besides
-# the -DDEBUG).
+# setting of the ccflags-y (or the older EXTRA_CFLAGS) variable mostly redundant
+# (besides the still useful -DDEBUG).
 # This simply helps us influence the build on a production kernel, forcing
 # generation of debug symbols, if so required. Also, realize that the DEBUG
 # macro is turned on by many CONFIG_*DEBUG* options; hence, we use a different
 # macro var name, MYDEBUG).
 MYDEBUG := n
+DBG_STRIP := y
 ifeq (${MYDEBUG}, y)
-
 # https://www.kernel.org/doc/html/latest/kbuild/makefiles.html#compilation-flags
 # EXTRA_CFLAGS deprecated; use ccflags-y
   ccflags-y   += -DDEBUG -g -ggdb -gdwarf-4 -Wall -fno-omit-frame-pointer -fvar-tracking-assignments
+  DBG_STRIP := n
 else
-  INSTALL_MOD_STRIP := 1
   ccflags-y   += -UDEBUG
 endif
 # We always keep the dynamic debug facility enabled; this allows us to turn
 # dynamically turn on/off debug printk's later... To disable it simply comment
 # out the following line
 ccflags-y   += -DDYNAMIC_DEBUG_MODULE
-
 KMODDIR ?= /lib/modules/$(shell uname -r)
-STRIP := ${CROSS_COMPILE}strip
 
-# gcc-10 issue:
-#ccflags-y  += $(call cc-option,--allow-store-data-races)
+# Gain access to kernel configs
+include $(KDIR)/.config
+
+# Strip the module? Note:
+# a) Only strip debug symbols else it won't load correctly
+# b) WARNING! Don't strip modules when using CONFIG_MODULE_SIG* crytographic security
+ifdef CONFIG_MODULE_SIG
+  DBG_STRIP := n
+endif
+ifdef CONFIG_MODULE_SIG_ALL
+  DBG_STRIP := n
+endif
+ifdef CONFIG_MODULE_SIG_FORCE
+  DBG_STRIP := n
+endif
+
 
 all:
 	@echo
-	@echo '--- Building : KDIR=${KDIR} ARCH=${ARCH} CROSS_COMPILE=${CROSS_COMPILE} ccflags-y=${ccflags-y} ---'
+	@echo '--- Building : KDIR=${KDIR} ARCH=${ARCH} CROSS_COMPILE=${CROSS_COMPILE} ccflags-y="${ccflags-y}" MYDEBUG=${MYDEBUG} DBG_STRIP=${DBG_STRIP} ---'
 	@${CC} --version|head -n1
 	@echo
 	make -C $(KDIR) M=$(PWD) modules
-	$(shell [ "${MYDEBUG}" != "y" ] && ${STRIP} --strip-debug ./${FNAME_C}.ko)
+	if [ "${DBG_STRIP}" = "y" ]; then \
+	   ${STRIP} --strip-debug ${FNAME_C}.ko ; \
+	fi
 install:
 	@echo
 	@echo "--- installing ---"
@@ -107,10 +141,11 @@ install:
 	@echo
 	@echo " [Now for the 'sudo make install' ]"
 	sudo make -C $(KDIR) M=$(PWD) modules_install
-	@echo " sudo depmod"
 	sudo depmod
-	@echo " [If !debug, stripping debug info from ${KMODDIR}/extra/${FNAME_C}.ko]"
-	$(shell if [ "${MYDEBUG}" != "y" ]; then sudo ${STRIP} --strip-debug ${KMODDIR}/extra/${FNAME_C}.ko; fi)
+	@echo " [If !debug and !(module signing), stripping debug info from ${KMODDIR}/extra/${FNAME_C}.ko]"
+	if [ "${DBG_STRIP}" = "y" ]; then \
+           sudo ${STRIP} --strip-debug ${KMODDIR}/extra/${FNAME_C}.ko ; \
+	fi
 nsdeps:
 	@echo "--- nsdeps (namespace dependencies resolution; for possibly importing ns's) ---"
 	make -C $(KDIR) M=$(PWD) nsdeps
@@ -119,10 +154,11 @@ clean:
 	@echo "--- cleaning ---"
 	@echo
 	make -C $(KDIR) M=$(PWD) clean
-# from 'indent'
+# from 'indent'; comment out if you want the backup kept
 	rm -f *~
 
-# Any usermode programs to build? Insert the build target(s) here
+# Any usermode programs to build? Insert the build target(s) below
+
 
 #--------------- More (useful) targets! -------------------------------
 INDENT := indent
@@ -168,12 +204,11 @@ sa_sparse:
 ifeq (,$(shell which sparse))
 	$(error ERROR: install sparse first)
 endif
-
 	make clean
 	@echo
 	@echo "--- static analysis with sparse ---"
 	@echo
-# if you feel it's too much, use C=1 instead
+# If you feel it's too much, use C=1 instead
 # NOTE: deliberately IGNORING warnings from kernel headers!
 	make -Wsparse-all C=2 CHECK="/usr/bin/sparse --os=linux --arch=$(ARCH)" -C $(KDIR) M=$(PWD) modules 2>&1 |egrep -v "^\./include/.*\.h|^\./arch/.*\.h"
 
@@ -207,29 +242,30 @@ endif
 	@echo
 	cppcheck -v --force --enable=all -i .tmp_versions/ -i *.mod.c -i bkp/ --suppress=missingIncludeSystem .
 
-# Packaging; just tar.xz as of now
-PKG_NAME := ${FNAME_C}
+# Packaging: just generates a tar.xz of the source as of now
 tarxz-pkg:
-	rm -f ../${PKG_NAME}.tar.xz 2>/dev/null
+	rm -f ../${FNAME_C}.tar.xz 2>/dev/null
 	make clean
 	@echo
 	@echo "--- packaging ---"
 	@echo
-	tar caf ../${PKG_NAME}.tar.xz *
-	ls -l ../${PKG_NAME}.tar.xz
-	@echo '=== package created: ../$(PKG_NAME).tar.xz ==='
-	@echo 'Tip: when extracting, to extract into a dir of the same name as the tar file,'
-	@echo ' do: tar -xvf ${PKG_NAME}.tar.xz --one-top-level'
+	tar caf ../${FNAME_C}.tar.xz *
+	ls -l ../${FNAME_C}.tar.xz
+	@echo '=== package created: ../$(FNAME_C).tar.xz ==='
+	@echo '        TIP: When extracting, to extract into a directory with the same name as the tar file, do this:'
+	@echo '              tar -xvf ${FNAME_C}.tar.xz --one-top-level'
 
 help:
 	@echo '=== Makefile Help : additional targets available ==='
 	@echo
-	@echo 'TIP: type make <tab><tab> to show all valid targets'
-	@echo
+	@echo 'TIP: Type make <tab><tab> to show all valid targets'
+	@echo 'FYI: KDIR=${KDIR} ARCH=${ARCH} CROSS_COMPILE=${CROSS_COMPILE} ccflags-y="${ccflags-y}" MYDEBUG=${MYDEBUG} DBG_STRIP=${DBG_STRIP}'
 
+	@echo
 	@echo '--- 'usual' kernel LKM targets ---'
 	@echo 'typing "make" or "all" target : builds the kernel module object (the .ko)'
-	@echo 'install     : installs the kernel module(s) to INSTALL_MOD_PATH (default here: /lib/modules/$(shell uname -r)/)'
+	@echo 'install     : installs the kernel module(s) to INSTALL_MOD_PATH (default here: /lib/modules/$(shell uname -r)/).'
+	@echo '            : Takes care of performing debug-only symbols stripping iff MYDEBUG=n and not using module signature'
 	@echo 'nsdeps      : namespace dependencies resolution; for possibly importing namespaces'
 	@echo 'clean       : cleanup - remove all kernel objects, temp files/dirs, etc'
 
@@ -246,17 +282,17 @@ help:
 	@echo ' sa_gcc        : run gcc with option -W1 ("Generally useful warnings") on the source file(s)'
 	@echo ' sa_flawfinder : run the static analysis flawfinder tool on the source file(s)'
 	@echo ' sa_cppcheck   : run the static analysis cppcheck tool on the source file(s)'
-	@echo 'TIP: use coccinelle as well (requires spatch): https://www.kernel.org/doc/html/v4.15/dev-tools/coccinelle.html'
+	@echo 'TIP: use Coccinelle as well: https://www.kernel.org/doc/html/v6.1/dev-tools/coccinelle.html'
 
 	@echo
 	@echo '--- kernel dynamic analysis targets ---'
 	@echo 'da_kasan   : DUMMY target: this is to remind you to run your code with the dynamic analysis KASAN tool enabled; requires configuring the kernel with CONFIG_KASAN On, rebuild and boot it'
 	@echo 'da_lockdep : DUMMY target: this is to remind you to run your code with the dynamic analysis LOCKDEP tool (for deep locking issues analysis) enabled; requires configuring the kernel with CONFIG_PROVE_LOCKING On, rebuild and boot it'
-	@echo 'TIP: best to build a debug kernel with several kernel debug config options turned On, boot via it and run all your test cases'
+	@echo 'TIP: Best to build a debug kernel with several kernel debug config options turned On, boot via it and run all your test cases'
 
 	@echo
 	@echo '--- misc targets ---'
 	@echo 'tarxz-pkg  : tar and compress the LKM source files as a tar.xz into the dir above; allows one to transfer and build the module on another system'
-	@echo ' Tip: when extracting, to extract into a dir of the same name as the tar file,'
-	@echo '  do: tar -xvf ${PKG_NAME}.tar.xz --one-top-level'
+	@echo '        TIP: When extracting, to extract into a directory with the same name as the tar file, do this:'
+	@echo '              tar -xvf ${FNAME_C}.tar.xz --one-top-level'
 	@echo 'help       : this help target'

ch8/lowlevel_mem/lowlevel_mem.c

@@ -88,7 +88,7 @@ static int bsa_alloc(void)
 	pr_info("1.  __get_free_page()     1 page    %px\n", gptr1);
 
 	/* 2. Allocate 2^bsa_alloc_order pages with the __get_free_pages() API */
-	numpg2alloc = powerof(2, bsa_alloc_order);	// returns 2^bsa_alloc_order
+	numpg2alloc = powerof(2, bsa_alloc_order);  /* returns 2^bsa_alloc_order */
 	gptr2 = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, bsa_alloc_order);
 	if (!gptr2) {
 		/* no error/warning printk now; see above comment */