[CS61C FA20] Lecture 13.2 - Compilation, Assembly, Linking, Loading: Compiler — Transcript

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1. 0:00and welcome back now we're going to see
2. 0:02the first and that call
3. 0:04the compiler so this is the beautiful
4. 0:07picture look at this beautiful beautiful
5. 0:09picture that shows you the
6. 0:10pretty complicated step to go from a c
7. 0:12program to a running program
8. 0:15we're going to see this over and over as
9. 0:16we kind of poke at the different pieces
10. 0:18of this
11. 0:19but let's kind of take a look here so
12. 0:20we're going to look at the compiler
13. 0:21stage here
14. 0:22but we're going to see overall the big
15. 0:24picture is
16. 0:25a compiler compiles the code from so
17. 0:28what's the input in the output of that
18. 0:29box
19. 0:30that's a c program and the output is a
20. 0:32dot s program
21. 0:33in fact that normally is hidden you can
22. 0:35say compile and the
23. 0:36output is a a dot out so this whole
24. 0:38thing typically is when you're done when
25. 0:40you say gcc
26. 0:41this whole thing is done and you you
27. 0:44often don't see those pieces
28. 0:46but work you could actually stop the
29. 0:47pieces and say oh that's when that
30. 0:49happens that's what happened that
31. 0:50happens
32. 0:50and so one of the features is for gcc if
33. 0:53you say dash s
34. 0:54it'll actually generate the dot s file
35. 0:56and that's the output of the compiler
36. 0:58and dot s is the input to the assembler
37. 1:00so we'll talk about what each of these
38. 1:01do
39. 1:02in the next series of lectures just want
40. 1:03to make sure i get the big picture here
41. 1:05in this first lecture
42. 1:09assembler takes the dot s produces a dot
43. 1:11o we'll see this again in more detail
44. 1:13the dot o
45. 1:14the linker takes the dot o and other dot
46. 1:16o files maybe from libraries
47. 1:17and includes them to make a running
48. 1:19program and the loader is
49. 1:21the operating system and the loader is
50. 1:22the guy that takes a run it takes a
51. 1:24program a dot out on disk
52. 1:25loads it into memory and sets up
53. 1:27everything needs to set up a lot of
54. 1:28complicated things need to set up
55. 1:30and then runs the program okay so that's
56. 1:32the big picture and again if you want to
57. 1:33see the output of a dot
58. 1:35of the compiler you type in dash capital
59. 1:37s to that
60. 1:38to make that work so this is the only
61. 1:41slide on this
62. 1:42the big picture is you're taking a dot c
63. 1:44you put out a dot s and here's the key
64. 1:46thing that you might not have understood
65. 1:49you're looking at this c code and you're
66. 1:51deciding as a compiler what to do and
67. 1:53you're producing assembler level code
68. 1:54you've already learned about risk 5
69. 1:55assembler that's what you produce that's
70. 1:57what the compiler has been doing all
71. 1:58along
72. 1:59dot s can be produced by two ways a
73. 2:01compiler can do it
74. 2:02you can turn optimization on and that
75. 2:04changes what the compiler is doing so
76. 2:05lots of ways you can feed things into
77. 2:07the compiler to change
78. 2:08those settings you could also hand
79. 2:11author.s files you could hand off the
80. 2:13risk 5 code
81. 2:14in fact we give you venus so you can
82. 2:15play with hand authoring it to
83. 2:17understand what it
84. 2:18is that it takes to translate hand
85. 2:20translate c
86. 2:22to dot s files it's not on you it's not
87. 2:24unheard of that we give you some c
88. 2:25code and ask you to do that on an exam
89. 2:27so make sure you're fluent enough with
90. 2:29the risk five not just oh okay that's
91. 2:31how it works on a wall
92. 2:32i was sitting back with my arms crossed
93. 2:34learning the whole time never did it
94. 2:35yourself no get your hands dirty
95. 2:36get in venus play with it so you
96. 2:38understand what it is and then
97. 2:40grab some really small c programs
98. 2:41compile them down and see how your hand
99. 2:43translation compares with how they
100. 2:44actually do it in fact at the end of
101. 2:45this lecture
102. 2:46we're going to hand translate a little
103. 2:47hello world just to show you how it all
104. 2:49works a little bit more complicated than
105. 2:50just
106. 2:51because there's some more things going
107. 2:52on but you'll see it we'll see by the
108. 2:54end of this for this lecture
109. 2:56here's the important thing there's an
110. 2:57idea of allowing for
111. 3:00a squishier that's squishy may not be
112. 3:04the word
113. 3:04but allowing for what we call pseudo
114. 3:06instructions and what that is
115. 3:08is you know what let's make it easier
116. 3:10for you to write
117. 3:11risk five code so we add these pseudo
118. 3:14instructions
119. 3:14that the assembler needs to then work
120. 3:16with later that
121. 3:18make it much easier to think about
122. 3:20writing assembler level programs for so
123. 3:22for example here's an example
124. 3:23a great example that we show you here so
125. 3:26move t1 t2 what this does is take the
126. 3:29value of two this is like t1 equals t2
127. 3:32in c code it says take the value of t2
128. 3:34and stuff it right in that register and
129. 3:36stuff it in the register t1
130. 3:38well it's really nice to think about
131. 3:40that and by the way i don't like move i
132. 3:41think move is a terrible name this
133. 3:43should be copy
134. 3:44because t1 is t2's value doesn't go away
135. 3:47it's really copy in the unix sense it's
136. 3:48really copy
137. 3:49uh in fact the order is opposite you
138. 3:51usually copy from this to that
139. 3:53so here you know it goes it goes from
140. 3:55the order of function goes
141. 3:57from t2 into t1 but
142. 4:00the point is i think this should be copy
143. 4:01not move my point of all of this is that
144. 4:04it's easier to say move than is to say
145. 4:07at
146. 4:07i t 1 t 2 0.
147. 4:10yeah that works too i get it t 2 plus
148. 4:13the
149. 4:13immediate zero goes into t1 therefore t1
150. 4:16gets the value of t2
151. 4:18so i could always be thinking at eyes
152. 4:20but isn't it easier just to write move
153. 4:22so we've added say we mean the assembler
154. 4:24community have added
155. 4:25pseudo instructions to make it easier to
156. 4:27write risk five assembly code that's
157. 4:29been true for all the assemblers that
158. 4:30i've been
159. 4:31you know familiar with uh mips risk
160. 4:34all of these allows for you to have
161. 4:37these pseudo instructions which just
162. 4:38make it easier to write in that assembly
163. 4:40level
164. 4:40okay that's it so again the compiler
165. 4:43takes.c code
166. 4:44produces.s assembler code that that s
167. 4:47file could contain
168. 4:48by the way that could also be hand
169. 4:49authored compiler or you
170. 4:51hand author at the end of the day you've
171. 4:52got s code and that could contain
172. 4:55pseudo-instructions and these sort of
173. 4:56pseudo-instructions just make it easier
174. 4:58to write that assembler all right
175. 4:59see the next lecture we learned about
176. 5:00the assembler take care