Hands-On System Programming with Linux: Explore Linux System Programming Interfaces, Theory, and Practice

Title Page......Page 2
Copyright and Credits......Page 3
Packt Upsell......Page 4
Contributors......Page 5
Table of Contents......Page 7
Preface......Page 19
Technical requirements......Page 27
Linux and the Unix operating system......Page 28
The Unix philosophy in a nutshell......Page 29
Everything is a process – if it\'s not a process, it\'s a file......Page 30
One tool to do one task......Page 33
Three standard I/O channels......Page 35
Word count ......Page 36
cat......Page 37
Combine tools seamlessly......Page 39
Plain text preferred......Page 41
Modular, designed to be repurposed by others......Page 42
Pseudocode......Page 43
The ABI......Page 45
Accessing a register\'s content via inline assembly......Page 49
Accessing a control register\'s content via inline assembly......Page 51
CPU privilege levels......Page 52
Privilege levels or rings on the x86......Page 53
Linux architecture......Page 56
Libraries......Page 57
System calls......Page 58
Linux – a monolithic OS......Page 59
What does that mean?......Page 60
Execution contexts within the kernel......Page 64
Interrupt context......Page 65
Summary......Page 66
Technical requirements......Page 67
Virtual memory......Page 68
No VM – the problem......Page 69
Objective......Page 70
Virtual memory......Page 72
Addressing 1 – the simplistic flawed approach......Page 76
Addressing 2 – paging in brief......Page 79
Paging tables – simplified......Page 81
Address-translation......Page 83
Process-isolation......Page 84
The programmer need not worry about physical memory......Page 85
Memory-region protection......Page 86
SIDEBAR :: Testing the memcpy() C program......Page 87
Process memory layout......Page 91
Segments or mappings......Page 92
Data segments......Page 94
Library segments......Page 95
Why a process stack?......Page 96
Peeking at the stack......Page 99
Advanced – the VM split......Page 102
Summary......Page 107
Resource limits......Page 108
Granularity of resource limits......Page 110
Available resource limits......Page 111
Hard and soft limits......Page 113
Querying and changing resource limit values......Page 116
Caveats......Page 118
Using prlimit(1) – examples......Page 119
API interfaces......Page 122
Code examples......Page 124
Permanence......Page 129
Summary......Page 130
Dynamic Memory Allocation......Page 131
The malloc(3) API......Page 132
malloc(3) – some FAQs......Page 135
The free API......Page 140
The calloc API......Page 142
The realloc API......Page 143
The realloc(3) – corner cases......Page 144
The reallocarray API......Page 145
Using the sbrk() API......Page 146
How malloc(3) really behaves......Page 150
Scenario 1 – default options......Page 151
Scenario 2 – showing malloc statistics......Page 152
Scenario 3 – large allocations option......Page 153
Advanced features......Page 154
Demand-paging......Page 155
Resident or not?......Page 157
Locking memory......Page 158
Limits and privileges......Page 159
Locking all pages......Page 163
Memory protection......Page 164
Memory protection – a code example......Page 165
LSM logs......Page 173
An experiment – running the memprot program on an ARM-32......Page 174
Using alloca to allocate automatic memory......Page 177
Summary......Page 181
Linux Memory Issues......Page 182
Common memory issues......Page 183
Incorrect memory accesses......Page 185
Test case 1: Uninitialized memory access......Page 186
Test case 2......Page 188
Test case 3......Page 189
Test case 4......Page 190
Test case 5......Page 191
Test case 6......Page 192
Test case 7......Page 193
Use-after-free/Use-after-return bugs......Page 194
Test case 8......Page 195
Test case 9......Page 196
Test case 10......Page 197
Test case 11......Page 200
Test case 12......Page 202
Test case 13 ......Page 205
Test case 13.1......Page 206
Test case 13.2......Page 207
Test case 13.3......Page 209
Undefined behavior......Page 210
Fragmentation......Page 211
Miscellaneous......Page 212
Summary......Page 213
Debugging Tools for Memory Issues......Page 214
Tool types......Page 215
Using Valgrind\'s Memcheck tool......Page 216
Valgrind pros and cons : a quick summary......Page 228
Sanitizer tools......Page 229
Sanitizer toolset......Page 230
Building programs for use with ASan......Page 231
Running the test cases with ASan......Page 232
AddressSanitizer (ASan) summary table......Page 245
AddressSanitizer pros and cons – a quick summary......Page 246
Glibc mallopt......Page 248
Malloc options via the environment ......Page 250
Code coverage while testing......Page 251
A mention of the malloc API helpers......Page 252
Summary......Page 254
Process Credentials......Page 255
The traditional Unix permissions model......Page 256
How the Unix permission model works......Page 257
Determining the access category......Page 260
Real and effective IDs......Page 262
A puzzle – how can a regular user change their password?......Page 265
The setuid and setgid special permission bits......Page 267
Setting the setuid and setgid bits with chmod......Page 268
Hacking attempt 1......Page 269
Querying the process credentials......Page 272
Code example......Page 273
Sudo – how it works......Page 274
Setting the process credentials......Page 275
Hacking attempt 2......Page 276
An aside – a script to identify setuid-root and setgid  installed programs......Page 280
setgid example – wall......Page 282
Giving up privileges......Page 285
Saved-set UID – a quick demo......Page 286
The setres[u|g]id(2) system calls......Page 289
Important security notes......Page 291
Summary......Page 292
Process Capabilities......Page 293
Motivation......Page 294
POSIX capabilities......Page 295
Viewing process capabilities via procfs......Page 298
Thread capability sets......Page 300
File capability sets......Page 301
Embedding capabilities into a program binary......Page 302
Getcap and similar utilities......Page 306
Wireshark – a case in point......Page 307
Setting capabilities programmatically......Page 308
How ls displays different binaries......Page 314
Permission models layering......Page 315
FYI – under the hood, at the level of the Kernel......Page 316
Summary......Page 317
Technical requirements......Page 318
Converting a program to a process......Page 319
The exec Unix axiom......Page 320
Key points during an exec operation......Page 321
Testing the exec axiom......Page 322
Experiment 2 – on the CLI, again......Page 323
The point of no return......Page 324
Family time – the exec family APIs......Page 325
Passing a zero as an argument......Page 328
Specifying the name of the successor......Page 329
The execlp API......Page 332
The execv API......Page 334
Exec at the OS level......Page 335
Summary table – exec family of APIs......Page 336
Code example......Page 337
Summary......Page 340
Process Creation......Page 341
How fork works......Page 342
Using the fork system call......Page 345
Fork rule #1......Page 346
Fork rule #2 – the return......Page 347
Fork rule #3......Page 353
Fork rule #4 – data......Page 355
Fork rule #5 – racing......Page 356
The process and open files......Page 357
Fork rule #6 – open files......Page 359
Open files and security......Page 361
Malloc and the fork......Page 362
COW in a nutshell......Page 364
Waiting and our simpsh project......Page 365
The Unix fork-exec semantic......Page 366
The need to wait......Page 367
Defeating the race after fork......Page 368
Putting it together – our simpsh project......Page 369
The wait API – details......Page 373
The scenarios of wait......Page 376
Wait scenario #2......Page 377
Fork bombs and creating more than one child......Page 378
The waitpid(2)......Page 380
The waitid (2)......Page 383
The actual system call......Page 384
Orphans......Page 386
Zombies......Page 387
Fork rule #7......Page 388
Summary......Page 389
Signaling - Part I......Page 390
The signal mechanism in brief......Page 391
Available signals......Page 394
The standard or Unix signals......Page 395
Handling signals......Page 398
Using the sigaction system call to trap signals......Page 399
The sigaction structure......Page 400
Signal masking with the sigprocmask API......Page 405
Querying the signal mask......Page 406
Reentrant functions......Page 409
Alternate ways to be safe within a signal handler......Page 411
Signal-safe atomic integers......Page 412
Powerful sigaction flags......Page 415
Zombies not invited......Page 416
No zombies! – the classic way......Page 417
No zombies! – the modern way......Page 418
Interrupted system calls and how to fix them with the SA_RESTART......Page 420
The once only SA_RESETHAND flag......Page 422
Signal behavior when masked......Page 423
Case 1 : Default : SA_NODEFER bit cleared......Page 424
Case 2 : SA_NODEFER bit set......Page 425
Running of case 1 – SA_NODEFER bit cleared [default]......Page 429
Running of case 2 – SA_NODEFER bit set......Page 430
Using an alternate signal stack......Page 433
Implementation to handle high-volume signals with an alternate signal stack......Page 434
Case 1 – very small (100 KB) alternate signal stack......Page 436
Case 2 : A large (16 MB) alternate signal stack ......Page 437
Summary......Page 438
Signaling - Part II......Page 439
Detailing information with the SA_SIGINFO......Page 440
The siginfo_t structure......Page 441
Getting system-level details when a process crashes......Page 445
Trapping and extracting information from a crash......Page 446
Register dumping......Page 451
Finding the crash location in source code......Page 455
What does errno do?......Page 457
The errno race......Page 458
Fixing the errno race......Page 459
Sleeping correctly......Page 460
The nanosleep system call......Page 461
Real-time signals......Page 464
Differences from standard signals......Page 465
Real time signals and priority......Page 466
Just kill \'em......Page 470
Agent 00 – permission to kill......Page 471
Are you there?......Page 472
Crude IPC......Page 473
Better IPC – sending a data item......Page 474
Sidebar – LTTng......Page 479
Synchronously waiting for signals......Page 481
Waiting forever or until a signal arrives......Page 482
The sigwait library API......Page 483
The sigwaitinfo and the sigtimedwait system calls......Page 488
The signalfd(2) API......Page 489
Summary......Page 492
Timers......Page 493
The good ol\' alarm clock......Page 494
Interval timers......Page 497
A simple CLI digital clock......Page 501
Obtaining the current time......Page 503
Trial runs......Page 505
A word on using the profiling timers......Page 506
The newer POSIX (interval) timers mechanism......Page 508
Creating and using a POSIX (interval) timer......Page 509
The arms race – arming and disarming a POSIX timer......Page 512
Example code snippet showing the workflow......Page 514
Figuring the overrun......Page 517
How fast is fast?......Page 518
Our react game – how it works......Page 519
React – trial runs......Page 521
The react game – code view......Page 523
The run:walk interval timer application......Page 527
A few trial runs......Page 528
The low – level design and code......Page 530
Timer lookup via proc......Page 534
Timers via file descriptors......Page 535
A quick note on watchdog timers......Page 537
Summary......Page 538
Multithreading with Pthreads Part I - Essentials......Page 539
What exactly is a thread?......Page 540
Resource sharing......Page 541
Multiprocess versus multithreaded......Page 545
Example 1 – creation/destruction – process/thread......Page 546
The multithreading model......Page 547
Example 2 – matrix multiplication – process/thread......Page 549
On a VM with 1 GB RAM, two CPU cores and parallelized make -j4......Page 554
On a VM with 1 GB RAM, one CPU core and sequential make -j1......Page 556
Taking advantage of potential parallelism......Page 557
Overlapping CPU with I/O......Page 558
Automatically taking advantage of modern hardware......Page 559
Context switching......Page 560
POSIX threads......Page 561
Pthreads and Linux......Page 562
Thread management – the essential pthread APIs......Page 563
Thread creation......Page 564
Termination......Page 567
The return of the ghost......Page 569
How many threads is too many?......Page 572
How many threads can you create?......Page 574
Code example – creating any number of threads......Page 576
How many threads should one create?......Page 578
Thread attributes......Page 580
Code example – querying the default thread attributes......Page 581
Joining......Page 584
The thread model join and the process model wait......Page 589
Checking for life, timing out......Page 590
Join or not?......Page 591
Parameter passing......Page 592
Passing a structure as a parameter......Page 593
Thread parameters – what not to do......Page 595
Get and set thread stack size......Page 597
Stack location......Page 598
Stack guards......Page 600
Summary......Page 604
Multithreading with Pthreads Part II - Synchronization......Page 605
The racing problem......Page 606
The pedagogical bank account example......Page 607
Critical sections......Page 610
Locking concepts......Page 611
Is it atomic?......Page 613
Dirty reads......Page 617
Locking guidelines......Page 618
Locking granularity......Page 620
Deadlock and its avoidance......Page 621
The ABBA deadlock......Page 622
Avoiding deadlock......Page 623
Using the pthread APIs for synchronization......Page 624
The mutex lock......Page 625
Seeing the race......Page 628
Mutex types......Page 631
The robust mutex attribute......Page 633
IPC, threads, and the process-shared mutex......Page 635
Priority inversion......Page 641
Watchdog timer in brief......Page 643
The Mars Pathfinder mission in brief......Page 645
Priority inheritance – avoiding priority inversion......Page 646
Summary of mutex attribute usage......Page 648
Timing out on a mutex lock attempt......Page 649
The reader-writer mutex lock......Page 650
The spinlock variant......Page 652
A few more mutex usage guidelines......Page 654
Is the mutex locked?......Page 655
Condition variables......Page 656
Using the condition variable......Page 657
A simple CV usage demo application......Page 659
CV broadcast wakeup......Page 663
Summary......Page 665
Thread safety......Page 666
Reentrant-safe versus thread-safe......Page 669
Thread safety via mutex locks......Page 671
Thread safety via function refactoring......Page 674
List of APIs not required to be thread-safe......Page 676
Refactoring glibc APIs from foo to foo_r......Page 677
Some glibc foo and foo_r APIs......Page 679
Thread safety via TLS ......Page 680
Thread safety via TSD ......Page 682
Canceling a thread......Page 683
The cancelability state......Page 684
The cancelability type......Page 685
Canceling a thread – a code example......Page 688
Cleaning up at thread exit......Page 690
Thread cleanup – code example......Page 691
Threads and signaling......Page 693
The POSIX solution to handling signals on MT......Page 694
Code example – handling signals in an MT app......Page 695
Threads vs processes – look again......Page 697
The multiprocess vs the multithreading model – pros of the MT model......Page 698
The multiprocess vs the multithreading model – cons of the MT model......Page 699
Pthreads – some FAQs......Page 700
Debugging multithreaded (pthreads) applications with GDB......Page 701
Summary......Page 703
The Linux OS and the POSIX scheduling model......Page 704
The Linux process state machine......Page 705
The sleep states......Page 706
What is real time?......Page 708
Types of real time......Page 709
Scheduling policies......Page 710
Peeking at the scheduling policy and priority......Page 712
The nice value......Page 713
CPU affinity......Page 714
Scheduling policy and priority APIs......Page 717
Code example – setting a thread scheduling policy and priority......Page 719
Soft real-time – additional considerations......Page 724
RTL – Linux as an RTOS......Page 725
Summary......Page 726
Advanced File I/O......Page 727
I/O performance recommendations......Page 728
The kernel page cache......Page 729
Via the posix_fadvise(2) API......Page 730
Via the readahead(2) API......Page 731
MT app file I/O with the pread, pwrite APIs......Page 732
Discontiguous data file – traditional approach......Page 734
Discontiguous data file – the SG – I/O approach......Page 736
File I/O via memory mapping......Page 739
The Linux I/O code path in brief......Page 740
Memory mapping a file for I/O......Page 743
File and anonymous mappings......Page 746
The mmap advantage......Page 748
Memory mapping – additional points......Page 750
Direct I/O (DIO)......Page 752
Asynchronous I/O (AIO)......Page 753
I/O technologies – a quick comparison......Page 754
Multiplexing or async blocking I/O – a quick note......Page 755
I/O schedulers......Page 756
Ensuring sufficient disk space......Page 758
Utilities for I/O monitoring, analysis, and bandwidth control......Page 759
Summary......Page 760
Troubleshooting and Best Practices......Page 761
perf......Page 762
The Linux proc filesystem......Page 763
Software engineering wisdom in a nutshell......Page 764
A programmer’s checklist – seven rules......Page 765
Using the Linux kernel\'s control groups......Page 766
Summary......Page 767
Other Books You May Enjoy......Page 768
Index......Page 771