wolfie's homepage

e-mail: mpolacek@redhat.com
jabber: phata@jabber.cz
irc: wolfie, #fit on IRCnet
FIT: records, course, wis, ftp
Interests:

• GNU Toolchain (libraries, compiler, linker, debugger)
• ELF
• women

Current employer: Red Hat

null | 500 albums | 1001 albums

(OLD) Stuff that matters

– behold--most of this is old and by no means perfect
– log of these source codes
– use gcc -std=gnu99 -D_GNU_SOURCE -D_FORTIFY_SOURCE=2 -Wall -Wextra -O2 -march=native
– COPYING
– INSTALL
– mmap scheme
– virtual address space layout, another
– gcc optimization table
– toolchain – view the whole process of compilation
– measuring the (un)likely macros
– linux-gate [CZECH]
– instrument-functions
– something about GCC printf optimization
– ELF notes
– fiddling with return address
– using grep
– introduction to autoconf and automake is here. With libtool.
– startup code compliant to the ELF i386 ABI with nice explanations. Taken from glibc.
– a word about errno
– a word about MALLOC_PERTURB_
– creating and inserting linux kernel module
– compiling GCC from scratch
– create a file system in a file within the current file system
– just strace output of int main() {} program
– using mudflap
– a mail about aliasing from Krister Walfridsson
– automated git update bash script
– creating static and dynamic libraries using gcc [CZECH]
– writing small ELF executable
– something about DCE and CSE, pure and const functions

Linux utilities

• ionice.c – get/set program io scheduling class and priority
• plmalloc.c – a simple memory allocator. PL stands for Pretty Lame. Example of usage.
• namei.c – follow a pathname until a terminal point is found
• mcookie.c – generator of random numbers for xauth
• blockdev.c – call block device ioctls from the command line
• dmesg.c – print out the contents of the kernel ring buffer
• size.c – bare bones implementation of the size utility
• rev.c – reverse lines of a file or files. Need rework.
• printenv.c – print environment variables
• showkey.c – examine the codes sent by the keyboard
• run algorithm for a certain amount of time
  • times.c
  • times.h
  • Makefile
  • times.tar.bz2
• a simple FIFO implementation
  • fifo.c
  • fifo.h
• error handler
  • die.c
  • die.h
• vlceksay.c – a cowsay modification
• sudoku
• • a console application to generate 9x9 sudoku
  • NB: old and ugly :)
  • sudoku.c
  • sudoku.h
  • Makefile
  • sudoku.tar.gz

Linux Kernel Modules

• hello.c – simple hello module
• chardev.c – create a char device. Sample session here
• kthread.c – simple kernel thread

GNU C

• constructor.c – demonstration of constructor and destructor attributes
• noreturn.c – example of __attribute__ ((__noreturn__)) , compile with -Wall
• check_birth_number.c – checks, if birth certificate number is valid, using label as value
• get_glibc_version.c – get glibc version

Strings

• concat.c – concatenate arbitrarily many strings
• untab.c – convert tabs to spaces
• format_string_attack.c – demonstration of format string attack using printf()

ELF

• don't forget to link with -lelf
• elf_pathnames.c – display a list of pathnames of the shared objects
• elf_filetype.c – get file type
• elf_header.c – print the ELF Executable Header
• elf_prg_header.c – print the ELF Program Header Tables
• elf_print_sections.c – print the names of ELF sections

GCC Inline Assembly

• do NOT use gcc optimizations or use -O0
• AT&T syntax: op-name src dest
• assign.c – assign a value to another value
• add.c – add two numbers
• multiply.c – multiply two numbers
• string.c – string routines
• direct_call.c – example of direct function call from inline assembly
• cpuid.c – get Vendor ID using CPUID opcode

Process Control

• fork_more.c – creating a few processes
• fork.c – example of fork function
• vfork.c – example of vfork function
• exit_status.c – example of exit statuses
• avoid_zombie.c – avoid zombie procesess by calling fork twice
• race_cond.c – program with a race condition
• race_cond_fixed.c – program with a race condition [FIXED]
• exec.c – example of exec functions
• acct.c – program to generate accounting data using acct function. Run as root, delete file `acct_log' afterwards
• examine_acct_log.c – print selected fields from system's accounting file (acct_log)
• times.c – time and execute all command-line arguments
• orphaned_pgroup.c – creating an orphaned process group

Memory Allocation

• memdup.c – duplicate memory block
• dynarr.c – dynamic arrays
• memswap.c – swap contents of two memory blocks
• mallinfo.c – examining the mallinfo structure
• memory_hooks.c – example of memory allocation hooks

Signals

• catch_signal.c – catch SIGUSR1 or SIGUSR2, display bunny or cow :-)
• signal_sets.c – example of signal sets
• raise.c – example of raise()
• sigsetjmp.c – example of signal masks, sigsetjmp() and siglongjmp()
• sigsuspend.c – protecting a critical region from a signal with sigsuspend()
• sigsuspend2.c – using sigsuspend() to wait for a global variable to be set
• psignal.c – example of psignal()

Pointers

• arrays_n_pointers.c – arrays and pointers addresses
• findfunc.c – calling function via char * (pointers to functions)
• arr_of_p_to_func.c – array of pointers to functions
• array_subscripting.c – array subscripting in C

Files and I/O

• can_seek.c – test whether stdin is capable of seeking
• file_hole.c – create a file with a hole in it
• print_file_flags.c – print file flags for specified descriptor
• readv.c – example of scatter read
• print_type.c – print type of a given file
• umask.c – example of umask function
• chmod.c – example of chmod function
• access.c – example of access function
• ls.c – list all the files in a directory
• unlink.c – open a file and then unlink it
• utime.c – example of utime function
• count_file_types.c – recursively descend a directory hierarchy, counting file types
• tree_walk.c – walk through a directory tree, using ftw()
• tree_walk2.c – walk through a directory tree, using nftw()
• size_of_dev.c – get size in bytes of block device
• print_dev_value.c – print st_dev and st_rdev values
• print_buffering.c – print buffering for various standard I/O streams
• tmpfile.c – demonstrate mkstemp and tmpfile functions
• tempnam.c – demonstrate tempnam function

Copying

• different approaches to copy a file
• copy_blk.c – copy file using fread() and fwrite()
• copy_char.c – copy file using getchar() and putchar()
• copy_fstr.c – copy file using fgets() and fputs()
• copy_getc.c – copy file using getc() and putc()
• copy_pipe.c – copy file using pipe
• copy_raw.c – copy file using read() and write()
• copy_raw2.c – copy file using read() and write() with buffer

ptrace

• intro.c – example of ptrace() syscall
• fetch_regs.c – fetch register values
• trace_ls.c – tracing write(2) when issued ls(1)
• trace_pid.c – tracing running process
• reverse_write.c – reverse the input passed to write(2)
• single-step.c – single step through the code

Stack

• stackloc.c – approximate location of the stack
• stack_align.c – test of stack align at i386

libcurl

• Compile with -lcurl
• curl_download.c – download a webpage using libcurl.
• curl_sepheaders.c – download a webpage, separate header and body

Networking

• daytime_server.c – daytime server, listens on port 1337
• daytime_client.c – daytime client

POSIX Threads

• pthread_create.c – create a thread
• pthread_create2.c – create two threads
• pthread_evens.c – compute even numbers in a thread
• pthread_detached.c – creating a detached thread, fragment only
• pthread_cs.c – critical section in a thread, fragment only
• pthread_tsd.c – per-thread log files implemented with TSD
• pthread_cleanup.c – demonstrating a thread cleanup handler, fragment only
• pthread_tsd.c – per-thread log files implemented with TSD
• mutex.c – example of pthread mutexes
• spin.c – example of pthread spinlocks
• barrier.c – example of pthread barriers
• pcleanup.c – another example of pthread cleanup handlers
• atfork.c – example of pthread_atfork(3P)
• pthread_attrsd.c – example of thread attributes object
• cancel.c – example of thread cancellation

Simulations

• LCG.c – simple linear congruent generator using rand(). Sample output.
• monte_carlo.c – compute Pi using Monte Carlo method. Sample output.
• mersenne_twister.c – Mersenne Twister algorithm for generation pseudorandom numbers. Sample output.

Other stuff

• time.c – when will time_t's wrap around?
• setjmp.c – non local jumps
• memory.c – how much memory can you allocate?
• exploit.c – stack exploit
• varg_list.c – variable argument list example
• getopt.c – parsing arguments using getopt()
• pipe.c – creating a pipe
• dangling.c – the dangling else problem
• ctype_test.c – testing the ctype.h header
• limits.c – basic properties of limits.h
• mmap.c – the mmap() system call example
• sysinfo.c – display system info
• byte_order.c – determine byte order on system
• uname.c – get the name of the current system
• getusername.c – get the name of the current user
• strftime.c – playing around with time
• rand_r.c – print 10 random numbers using rand_r
• dlfcn.c – wrapper for malloc()/free() using <dlfcn.h>. Compile with -ldl
• getuid.c – get an user ID
• posix_version.c – display POSIX version
• atexit.c – example of atexit() function
• readterm.c – reading from the terminal
• readkey.c – reading from the terminal in noncanonical mode. End with q/Q.
• shell-like.c – read commands from stdin and execute them
• show_error.c – demonstrate strerror and perror
• sysconf.c – print some of limits using sysconf
• syscall.c – example of indirect system call
• auxv.c – get AT_SYSINFO from ELF auxiliary vector
• linux_version.c – display linux version
• fd-bench.c – check the cost of opening a file descriptor
• tlb_miss.c – TLB miss measurement on x86 CPUs. Run as root, SIGSEGV otherwise.
• setjmp_test_vars.c – effect of longjmp on various types of variables
• rlimits.c – print the current resource limits
• fmemopen.c – example of fmemopen() / open_memstream() functions
• backtrace.c – example of backtraces
• memset.c – implementation of memset using Duff's device
• obstacks.c – example of obstacks
• aio.c – example of asynchronous read using aio_read()
• rpmatch.c – example of rpmatch(3)
• dlmath.c – dynamically load the math library
• atomic.c – playing with kernel's atomic operations
• vt.c – display the character and screen attributes under the cursor of the 2nd VT
• getpwuid.c – example of getpwuid() and getgrgid()
• hsearch.c – example of hash table using hsearch()
• bswap.c – example of bswap_*()
• bogo.c – computing the BogoMIPS value on x86
• timerfd.c – example of timerfd*(2) -- timers that notify via file fds
• eventfd.c – example of eventfd(2) -- create a file descriptor for event notification
• shm.c – example of POSIX shm_*() functions
• sem1.c – example of POSIX sem_*() functions
• sem2.c – example of POSIX sem_*() functions
• swapcontext.c – example of swapcontext(3)
• popen.c – example of popen(3)
• rprintf.c – customizing printf(3)
• bsearch.c – example of bsearch(3)
• subopt.c – example of subopt(3)
• hash.c – example of various hash string functions
• mincore.c – print out which blocks of the file are cached

Hello World programs

• hello1.c – common Hello World program
• hello2.c
  • compile with gcc -ffreestanding -nostartfiles hello2.c -o hello2
  • smaller executable file than `hello1'
  • links with the same DSOs (Dynamic Shared Objects)
  • uses the dynamic linker:

    $ readelf -l hello2 | grep INTERP > /dev/null && echo yes || echo no
    yes
    
    $ file -b hello2
    ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), 
    
    dynamically linked (uses shared libs), not stripped
    

• hello3.c
  • compile with gcc -ffreestanding -nostartfiles hello3.c -o hello3
  • now we have indirect syscalls
  • links with the same DSOs (Dynamic Shared Objects)
  • still uses the dynamic linker:

    $ readelf -l hello3 | grep INTERP > /dev/null && echo yes || echo no
    yes
    
    $ file -b hello3
    ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), 
    
    dynamically linked (uses shared libs), not stripped
    

• hello4.c
  • compile with gcc -ffreestanding -nostartfiles -nostdlib hello4.c -o hello4
  • using __asm__
  • no shared libraries => no dynamic linking:

    $ readelf -l hello4 | grep INTERP > /dev/null && echo yes || echo no
    no
    
    $ file -b hello4
    ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), 
    
    statically linked, not stripped
    

  • empty data segment:

    $ size hello4 | cut -f2 | tail -1
          0
    

ncurses

• howto
• gnu ftp
• compile with -lncurses
• color_nc.c – example 

Obfuscated C Code

• obfus1.c
• obfus2.c

wtf

• wtf1.c – what does 'x = sizeof(int) * p' mean?

Makefiles

• Makefile
• Makefile

THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.



---

$ Sat Dec 4 12:16:41 CET 2010