Bootstrapping

1
Bootstrapping
Programming Language Translators

• Prepared by
• Manuel E. Bermúdez, Ph.D.
• Associate Professor
• University of Florida

2
Bootstrapping

• The notion of implementing a language, by means
  of using (part of) that languages own
  implementation.
• Notation T-diagram

Source
Target
Language Written in
3
Bootstrapping

• Diagram Purpose

APPLICATION
APPLICATION
C
C
M
M
M
Object Coincides
Source Coincides
Execution
4
Bootstrapping

• Example We wish to have a Pascual compiler for
  a new Processor, M.
• How do we get it ?
• Possibility 1 Write the compiler directly by
  hand, in machine language? In assembly language ?
  ?

P
M
M
5
Bootstrapping

• Possibility 2 Write the Pascal compiler in
  some other language L, that is already
  implemented on M. Then, compile the compiler.
• But, ... this is probably too much work.

P M
P M
L
L
M
M
M
L Compiler
6
Bootstrapping

• Possibility 3 First, implement P, a subset of
  Pascal. Then, write the desired compiler in P,
  and compile it.
• Step 1
• Now P is implemented.

P M
P M
L
L
M
M
M
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Bootstrapping

• Step 2
• If P is choosen well, the P -gt M compiler and the
  Pascal -gt M compiler (in P) together, are easier
  to write than the Pascal -gt M (in L) compiler.
• Theoretically, this process can go on
  indefinitely, bootstrapping up the level of the
  language. In practice, however, new constructs
  interfere with each other (and with old ones),
  until further bootstrapping becomes ummanageable

Pascal M
Pascal M
P
P
M
M
M
Write this
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Bootstrapping

• Example Now, lets suppose we wish to port
  Pascal to a new machine, M.
• Possibility 1 Same as for M.
• Possibility 2 Same as for M.
• Possibility 3 Same as for M.

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Bootstrapping

• Possibility 4
• Step 1 Same as for M (implement P on M).
• Step 2 Modify the Pascal compiler.

Pascal
M
By hand
P
Pascal M
Pascal M
P
P
M
M
M
10
Bootstrapping

• Possibility 5 Dont use P! Use the
  implementation of Pascal on M instead.
• Step 1

Pascal
M
By hand
P
Pascal M
Pascal M
Pascal
M
Pascal
M
M
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Bootstrapping

• Step 2
• Note Possibility 5 is called cross-compiling.

Pascal M
Pascal M
Pascal
M
Pascal
M
M
By hand
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Bootstrapping

• Many compilers undergo a long chain of
  bootstrapping steps. For example, XPL (a dialect
  of PL/I), was written first in Algol, then in
  XPL, and ported to a B5500 and then an IBM 360.
  Eight bootstraping steps were required.