This talk examines why learning C and Assembly is useful to all programmers and one way a programmer might begin to embark on this journey.

1. All programmers
must
learn C and Assembly
Joe Damato
@joedamato

2. i like computers
i once had a blog called
timetobleed.com
@joedamato
greetings

3. packagecloud.io
@packagecloudio

6. ?

10. Become proficient in C and
x86 assembly

12. hardware
OS
system libs
c + asm
c + asm
c + asm

13. “The farther back you can
look, the farther forward you
are likely to see.”
- Churchill, maybe?

14. hardware
OS
system libs
c + asm
c + asm
c + asm
Ruby VM c + asm
ruby codeYOUR CODE!

15. hardware
OS
system libs
Python VM
c + asm
c + asm
c + asm
c + asm
python codeYOUR CODE!

16. hardware
OS
system libs
node.js
c + asm
c + asm
c + asm
c + asm
js codeYOUR CODE!

26. read two things only
•man pages
•source code

27. apt-get source
•apt-get source strace
•apt-get source ltrace
•apt-get source gdb

29. where to invest first penny?
ptrace &
ptrace-related tools
(strace, ltrace, gdb, …)

30. hardware
OS
system libs
c + asm
c + asm
c + asm
ptrace gives you this

31. hardware
OS
system libs
Ruby VM
c + asm
c + asm
c + asm
c + asm
ruby codeYOUR CODE!

32. hardware
OS
system libs
Python VM
c + asm
c + asm
c + asm
c + asm
python codeYOUR CODE!

33. hardware
OS
system libs
node.js
c + asm
c + asm
c + asm
c + asm
js codeYOUR CODE!

34. [sl]trace
• read man page for strace
• read it again
• read man page for ltrace
• read it again
• start using both — trace everything

35. [sl]trace
• they will be confusing
• keep using them

36. don’t just learn how to use
the tool
learn how the tool works

37. ptrace
• read the man page
• read it again
• read it again
• ….
• read a program that uses it (strace)

38. why ptrace?
• strace
• ltrace
• gdb
• rtld
• libthread_db

41. but joe i’m really nice with
the monads and they
doesn’t afraid of side
effects

43. (you end up with
an assembly
program anyway
lols)

45. and now 2 bugs
you can find with
strace

46. Story Time
gettimeofday
vDSO
strace

47. read more:
https://bit.ly/aws-ec2-slow

48. Story Time
getCurrentThreadCpuTime
POSIX clocks
Kernel 2.6.12
strace

49. read more:
https://bit.ly/java-slow

50. “threads are slow”

51. “context switches
are expensive/
slow/…”

54. a 7 year old bugfix
for XFree86 broke
threads on Linux

55. Story Time
64bit computers
XFree86 Modules
mmap

56. June 29, 2001

57. “This adds a new mmap
flag to force mappings into
the low 32bit address
space [MAP_32BIT].
Useful e.g. for XFree86′s
ELF loader […]”

58. Nov 11, 2002

59. “532. Fixed module loader
to map memory in the low
32bit address space on
x86-64 (Egbert Eich).”

60. Jan 4, 2003

62. “Make MAP_32BIT […]
only map in the first 31bit,
because it is usually used
to map small model code.”

63. Story Time
ELF small code model
31bit mapping

64. So: MAP_32BIT ….
only maps 31 bit

67. Mar 4, 2003

68. /* For Linux/x86-64 we have one
extra requirement: the stack must
be in the first [32bit].
Otherwise [we cant use threads].
*/
glibc

69. May 9, 2003

70. /* We prefer to have [memory]
allocated in the low [32bit]
since this allows faster
context switches.
*/
glibc

71. justification for
MAP_32BIT in
glibc changed

72. Aug 13, 2008

73. “Pardo” report
https://lkml.org/lkml/2008/8/12/423

74. “Pardo” report

75. “Pardo” report
• MAP_32bit used in glibc for
“speed”
• (actually only maps into 31bits)
• 31bits is a lot smaller than 32bits

76. “Pardo” report
pardo filled the 31bit 1GB space.
subsequent allocations fell back
to the retry mechanism (which
was added for speed)

77. “Pardo” report
retry mechanism
causes a linear
search

78. linear search of large
lists is bad and slow

79. the thing added for
speed

80. made it 1000x slower

82. How was this
fixed?

83. fix this by adding
another mmap flag

85. MAP_STACK
is added.

86. to be used to
allocate thread
stacks

87. (it does nothing)

89. MAP_32BIT
remains.

90. (only maps 31bits)

92. June 29, 2001: MAP_32BIT added to kernel
Nov 11, 2002: XFree86 updated to use MAP_32BIT
time or w/e
Jan 4, 2003: MAP_32BIT updated for ELF small code
Feb 12, 2003: wrmsr slowness reported
Mar 4, 2003: MAP_32BIT added to glibc
May 9, 2003: MAP_32BIT retry added to glibc
Aug 13, 2008:“Pardo” report
Aug 13, 2008: MAP_STACK
Aug 15, 2008: glibc updated

93. so

94. learning C and assembly
means

95. you can debug anything built on
a modern day computer

96. thanksJoe Damato
@joedamato