1-Cousins of Compiler preprocessor,assembler, linker and loader.ppt

this is about the cousins of compiler. here we have explained the cousins of compiler and their functionalities

1. Compiler

Construction
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2. Cousins of Compiler
Preprocessors
Assemblers
Loader and Link-Editor
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3. Preprocessors
They produce input to compiler. They may
perform the following functions:
1.Macro Processing
2.File Inclusion
3.Rational preprocessors (they augment older
languages with modern flow of control)
4.Language extensions
(Equel is a database query language embedded in C)
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4. Assembler
Some compiler produces assembly code that is
passed to an assembler for processing.
Other compilers produces relocatable machine
code that can be passed directly to the
loader/link-editor.
Assembly code is a mnemonic version of machine
code, in which names are used instead of binary
codes for operations. e.g.
MOVa,R1
ADD#2,R1
MOVR1,b
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5. Two-Pass Assembly
The assembler makes two passes over the input.
A pass consist of reading the input file once.
In the first pass, all the identifiers that denote
storage locations are found and stored in a
symbol table (separate from that of compiler)
Identifiers are assigned storage locations as they
are encountered for the first time
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6. For Example
The symbol table might contains the entries as
shown below: (Assuming that a word consists of 4
bytes, and the addresses are assigned starting
from bytes)
IDENTIFIER ADDRESS
a 0
b 4
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7. Two-Passes Assembly
In the second pass, the assembler scans the input
again
This time it translate each operation code into the
sequence of bits representing that operation in
machine language, it also translate each
identifier representing a location into the address
given for that identifier in the symbol table.
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8. Two-Passes Assembly
The output of the second pass is usually
relocatable machine code, meaning that it can
be loaded starting at any location L in memory;
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9. Example
The following is a hypothetical machine code for
previous example:
0001 010000000000 *
0011 011000000010
0010 010000000000 *
Instruction code Register Address mode Memory
address
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10. Continued……..
If L = 00001111 i.e. 15 then a and b would be at
location 15 and 19, respectively, and the
instructions would now appear as absolute code:
0001010000001111
0011011000000010
0010010000010011
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11. Loader and Link-Editor
It perform two functions of loading and link-
editing
Loading process consist of taking relocatable
machine code, altering the relocatable
addresses and placing the altered instruction and
data in memory at proper location.
Link-Editor make a single program from several
files of relocatable machine code.
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12. The Grouping of Phases
Activities from more than one phases can be
grouped together.
Front and Back Ends
Passes
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13. Front and Back Ends
Front End consist of those phases, or part of
phases that depends primarily on the source
language and are independent of target
machine. It normally includes:
1.Lexical analysis
2.Syntactic analysis
3.The creation of Symbol Table
4.Semantic analysis
5.The generation of Intermediate Code
6.Certain amount of Code optimization
7.Error Handling
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14. Front and Back Ends
The Back End includes those portions of the
compiler that depend on the target machine,
and are independent of source language. It
includes:
1.Code Optimization
2.Code Generation
3.Necessary Error handling and Symbol-Table
operations.
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15. Advantages of Front End and
Back End
If we want to write new compiler for the same
machine then only the Front End of the compiler
change while the Back End remain the same.
Similarly if we want to write the compiler for new
machine then the front end of the compiler
remain the same and back end of the compiler is
changed.
It is also good idea to compile several different
languages into same intermediate language and
use a common back end for different front ends.
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16. Example:
A C Language compiler may have more than one
back ends each for a different machines i.e.
It means that one back end will work for IBM
Machine and 2nd for Apple with a single front end
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C-Language
Compiler
Front End
Back End
IBM
Back End
Apple

17. Example:
Suppose we have a C- Compiler with Front End
and Back End and now for FORTRON compiler we
have only to change its front end for FORTRAN
and its Back End will remain the same.
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Target Language
Back End
FORTRAN-Compiler
Front End
C-Compiler
Front End

18. Passes
Several phases of compilation are usually
implemented in a single pass consisting of reading
an input file and writing an output file.
The grouped phases must be interleaved during
the pass. For Example:
lexical analysis, syntax analysis, semantic analysis
and intermediate code generation might be
grouped together into one pass
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19. Passes
It is desirable to have few passes, since it takes
time to read and write intermediate files.
On the other hand, if we group several phases
into one pass, we may be forced to keep the
entire program in memory, because one phase
may need information in a different order than a
previous phase produce it.
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