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Kaiwan N Billimoria
183
ch6/foreach/thrd_showall/Makefile
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183
ch6/foreach/thrd_showall/Makefile
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# ch6/foreach/thrd_showall/Makefile
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# ***************************************************************
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# This program is part of the source code released for the book
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# "Linux Kernel Programming"
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# (c) Author: Kaiwan N Billimoria
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# Publisher: Packt
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# GitHub repository:
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# https://github.com/PacktPublishing/Linux-Kernel-Programming
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#
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# From: Ch 5 : Writing Your First Kernel Module LKMs, Part 2
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# ***************************************************************
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# Brief Description:
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# A 'better' Makefile template for Linux LKMs (Loadable Kernel Modules); besides
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# the 'usual' targets (the build, install and clean), we incorporate targets to
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# do useful (and indeed required) stuff like:
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# - adhering to kernel coding style (indent+checkpatch)
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# - several static analysis targets (via sparse, gcc, flawfinder, cppcheck)
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# - two 'dummy' dynamic analysis targets (KASAN, LOCKDEP)
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# - a packaging (.tar.xz) target and
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# - a help target.
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#
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# To get started, just type:
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# make help
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#
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# For details, please refer the book, Ch 5.
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# To support cross-compiling for kernel modules:
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# For architecture (cpu) 'arch', invoke make as:
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# make ARCH=<arch> CROSS_COMPILE=<cross-compiler-prefix>
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ifeq ($(ARCH),arm)
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# *UPDATE* 'KDIR' below to point to the ARM Linux kernel source tree on your box
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KDIR ?= ~/rpi_work/kernel_rpi/linux
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else ifeq ($(ARCH),arm64)
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# *UPDATE* 'KDIR' below to point to the ARM64 (Aarch64) Linux kernel source
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# tree on your box
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KDIR ?= ~/kernel/linux-4.14
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else ifeq ($(ARCH),powerpc)
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# *UPDATE* 'KDIR' below to point to the PPC64 Linux kernel source tree on your box
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KDIR ?= ~/kernel/linux-4.9.1
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else
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# 'KDIR' is the Linux 'kernel headers' package on your host system; this is
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# usually an x86_64, but could be anything, really (f.e. building directly
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# on a Raspberry Pi implies that it's the host)
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KDIR ?= /lib/modules/$(shell uname -r)/build
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endif
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PWD := $(shell pwd)
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obj-m += thrd_showall.o
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EXTRA_CFLAGS += -DDEBUG
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all:
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@echo
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@echo '--- Building : KDIR=${KDIR} ARCH=${ARCH} CROSS_COMPILE=${CROSS_COMPILE} EXTRA_CFLAGS=${EXTRA_CFLAGS} ---'
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@echo
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make -C $(KDIR) M=$(PWD) modules
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install:
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@echo
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@echo "--- installing ---"
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@echo
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make -C $(KDIR) M=$(PWD) modules_install
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clean:
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@echo
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@echo "--- cleaning ---"
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@echo
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make -C $(KDIR) M=$(PWD) clean
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rm -f *~ # from 'indent'
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#--------------- More (useful) targets! -------------------------------
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INDENT := indent
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# code-style : "wrapper" target over the following kernel code style targets
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code-style:
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make indent
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make checkpatch
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# indent- "beautifies" C code - to conform to the the Linux kernel
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# coding style guidelines.
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# Note! original source file(s) is overwritten, so we back it up.
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indent:
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@echo
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@echo "--- applying kernel code style indentation with indent ---"
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@echo
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mkdir bkp 2> /dev/null; cp -f *.[chsS] bkp/
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${INDENT} -linux --line-length95 *.[chsS]
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# add source files as required
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# Detailed check on the source code styling / etc
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checkpatch:
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make clean
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@echo
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@echo "--- kernel code style check with checkpatch.pl ---"
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@echo
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$(KDIR)/scripts/checkpatch.pl --no-tree -f --max-line-length=95 *.[ch]
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# add source files as required
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#--- Static Analysis
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# sa : "wrapper" target over the following kernel static analyzer targets
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sa:
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make sa_sparse
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make sa_gcc
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make sa_flawfinder
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make sa_cppcheck
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# static analysis with sparse
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sa_sparse:
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make clean
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@echo
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@echo "--- static analysis with sparse ---"
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@echo
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# if you feel it's too much, use C=1 instead
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make C=2 CHECK="/usr/bin/sparse" -C $(KDIR) M=$(PWD) modules
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# static analysis with gcc
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sa_gcc:
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make clean
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@echo
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@echo "--- static analysis with gcc ---"
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@echo
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make W=1 -C $(KDIR) M=$(PWD) modules
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# static analysis with flawfinder
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sa_flawfinder:
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make clean
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@echo
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@echo "--- static analysis with flawfinder ---"
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@echo
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flawfinder *.[ch]
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# static analysis with cppcheck
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sa_cppcheck:
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make clean
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@echo
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@echo "--- static analysis with cppcheck ---"
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@echo
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cppcheck -v --force .
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# Packaging; just tar.xz as of now
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PKG_NAME := lkm_template
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tarxz-pkg:
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rm -f ../${PKG_NAME}.tar.xz 2>/dev/null
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make clean
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@echo
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@echo "--- packaging ---"
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@echo
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tar caf ../${PKG_NAME}.tar.xz *
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ls -l ../${PKG_NAME}.tar.xz
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@echo '=== package created: ../$(PKG_NAME).tar.xz ==='
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help:
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@echo '=== Makefile Help : additional targets available ==='
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@echo
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@echo 'TIP: type make <tab><tab> to show all valid targets'
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@echo
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@echo '--- 'usual' kernel LKM targets ---'
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@echo 'typing "make" or "all" target : builds the kernel module object (the .ko)'
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@echo 'install : installs the kernel module(s) to INSTALL_MOD_PATH (default: /lib/modules/$(shell uname -r)/)'
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@echo 'clean : cleanup - remove all kernel objects, temp files/dirs, etc'
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@echo
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@echo '--- kernel code style targets ---'
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@echo 'code-style : "wrapper" target over the following kernel code style targets'
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@echo ' indent : run the $(INDENT) utility on source file(s) to indent them as per the kernel code style'
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@echo ' checkpatch : run the kernel code style checker tool on source file(s)'
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@echo
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@echo '--- kernel static analyzer targets ---'
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@echo 'sa : "wrapper" target over the following kernel static analyzer targets'
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@echo ' sa_sparse : run the static analysis sparse tool on the source file(s)'
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@echo ' sa_gcc : run gcc with option -W1 ("Generally useful warnings") on the source file(s)'
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@echo ' sa_flawfinder : run the static analysis flawfinder tool on the source file(s)'
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@echo 'TIP: use coccinelle as well (requires spatch): https://www.kernel.org/doc/html/v4.15/dev-tools/coccinelle.html'
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@echo
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@echo '--- kernel dynamic analysis targets ---'
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@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'
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@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'
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@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'
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@echo
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@echo '--- misc targets ---'
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@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'
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@echo 'help : this help target'
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156
ch6/foreach/thrd_showall/thrd_showall.c
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156
ch6/foreach/thrd_showall/thrd_showall.c
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@@ -0,0 +1,156 @@
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/*
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* ch6/foreach/thrd_showall/thrd_showall.c
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***************************************************************
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* This program is part of the source code released for the book
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* "Linux Kernel Programming" 2E
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* (c) Author: Kaiwan N Billimoria
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* Publisher: Packt
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* GitHub repository:
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* https://github.com/PacktPublishing/Linux-Kernel-Programming_2E
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*
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* From: Ch 6 : Kernel and MM Internals Essentials
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****************************************************************
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* Brief Description:
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* This kernel module iterates over the task structures of all *threads*
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* currently alive on the box, printing out some details.
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* We use the do_each_thread() { ... } while_each_thread() macros to do
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* so here.
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*
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* For details, please refer the book, Ch 6.
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*/
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//#define pr_fmt(fmt) "%s: " fmt, KBUILD_MODNAME
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#include <linux/init.h>
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#include <linux/module.h>
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#include <linux/sched.h> /* current() */
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#include <linux/version.h>
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#if LINUX_VERSION_CODE > KERNEL_VERSION(4, 10, 0)
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#include <linux/sched/signal.h>
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#endif
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MODULE_AUTHOR("Kaiwan N Billimoria");
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MODULE_DESCRIPTION("LKP 2E:ch6/foreach/thrd_showall: \
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demo to display all threads by iterating over the task list");
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MODULE_LICENSE("Dual MIT/GPL");
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MODULE_VERSION("0.2");
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/* Display just CPU 0's idle thread, i.e., the pid 0 task,
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* the (terribly named) 'swapper/n'; n = 0, 1, 2,...
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* Again, init_task is always the task structure of the first CPU's
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* idle thread, i.e., we're referencing swapper/0.
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*/
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static inline void disp_idle_thread(void)
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{
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struct task_struct *t = &init_task;
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/* We know that the swapper is a kernel thread */
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pr_info("%8d %8d 0x%px 0x%px [%16s]\n",
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t->pid, t->pid, t, t->stack, t->comm);
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}
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static int showthrds(void)
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{
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struct task_struct *g = NULL, *t = NULL; /* 'g' : process ptr; 't': thread ptr */
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int nr_thrds = 1, total = 1; /* total init to 1 for the idle thread */
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#define BUFMAX 256
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#define TMPMAX 128
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char buf[BUFMAX], tmp[TMPMAX];
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const char hdr[] =
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"------------------------------------------------------------------------------------------\n"
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" TGID PID current stack-start Thread Name MT? # thrds\n"
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"------------------------------------------------------------------------------------------\n";
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pr_info("%s", hdr);
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disp_idle_thread();
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/*
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* The do_each_thread() / while_each_thread() is a pair of macros that iterates over
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* _all_ task structures in memory.
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* The task structs are global of course; this implies we should hold a lock of some
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* sort while working on them (even if only reading!). So, doing
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* read_lock(&tasklist_lock);
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* [...]
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* read_unlock(&tasklist_lock);
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* BUT, this lock - tasklist_lock - isn't exported and thus unavailable to modules.
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* So, using an RCU read lock is indicated here (this has been added later to this code).
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* FYI: a) Ch 12 and Ch 13 cover the details on kernel synchronization.
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* b) Read Copy Update (RCU) is a complex synchronization mechanism; it's
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* conceptually explained really well in this blog article:
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* https://reberhardt.com/blog/2020/11/18/my-first-kernel-module.html
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*/
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rcu_read_lock();
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do_each_thread(g, t) { /* 'g' : process ptr; 't': thread ptr */
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// task_lock(t);
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get_task_struct(t); // take a reference to the task struct
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snprintf(buf, BUFMAX-1, "%8d %8d ", g->tgid, t->pid);
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/* task_struct addr and kernel-mode stack addr */
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snprintf(tmp, TMPMAX-1, " 0x%px", t);
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/*
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* To concatenate the temp string to our buffer, we could go with the
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* strncat() here; flawfinder, though, points out this is potentially
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* dangerous; so we simply use another snprintf() to achieve the same.
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* Why not use strlcat() instead? Here, it runs into trouble - being
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* called in an atomic context, which isn't ok (due to the
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* might_sleep() within it's code)...
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*/
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snprintf(buf, BUFMAX-1, "%s%s 0x%px", buf, tmp, t->stack);
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if (!g->mm) { // kernel thread
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/* One might question why we don't use the get_task_comm() to obtain
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* the task's name here; the short reason: it causes a deadlock! We
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* shall explore this (and how to avoid it) in some detail in Ch 17 -
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* Kernel Synchronization Part 2. For now, we just do it the simple way
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*/
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snprintf(tmp, TMPMAX-1, " [%16s]", t->comm);
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} else {
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snprintf(tmp, TMPMAX-1, " %16s ", t->comm);
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}
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snprintf(buf, BUFMAX-1, "%s%s", buf, tmp);
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/* Is this the "main" thread of a multithreaded process?
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* We check by seeing if (a) it's a userspace thread,
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* (b) it's TGID == it's PID, and (c), there are >1 threads in
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* the process.
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* If so, display the number of threads in the overall process
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* to the right..
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*/
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nr_thrds = get_nr_threads(g);
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if (g->mm && (g->tgid == t->pid) && (nr_thrds > 1)) {
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snprintf(tmp, TMPMAX-1, " %3d", nr_thrds);
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snprintf(buf, BUFMAX-1, "%s%s", buf, tmp);
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}
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snprintf(buf, BUFMAX-1, "%s\n", buf);
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pr_info("%s", buf);
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total++;
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memset(buf, 0, sizeof(buf));
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memset(tmp, 0, sizeof(tmp));
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put_task_struct(t); // release reference to the task struct
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// task_unlock(t);
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} while_each_thread(g, t);
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rcu_read_unlock();
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return total;
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}
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static int __init thrd_showall_init(void)
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{
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int total;
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pr_info("%s: inserted\n", KBUILD_MODNAME);
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total = showthrds();
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pr_info("%s: total # of threads on the system: %d\n", KBUILD_MODNAME, total);
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return 0; /* success */
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}
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static void __exit thrd_showall_exit(void)
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{
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pr_info("%s: removed\n", KBUILD_MODNAME);
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}
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module_init(thrd_showall_init);
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module_exit(thrd_showall_exit);
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