Compilation

After preprocessing, our next goal is produce assembly language for the preprocesed file. There are a number of approaches to this; we could invoke the preprocessor on each .c file, produce a .i file and then pass this to the compiler; or (a lot less trouble) just pass the .c files to the compiler, which will detect that the sources have not been preprocessed, so instead will preprocess them and then run them through the compiler:

gcc -S -I ../m4 -I ../ main.c freeze.c stackovf.c temp.c

Note that this will produce a number of errors - mine produced the following output:

     $ gcc -I. -I.. -I../m4 -S main.c freeze.c stackovf.c temp.c
     In file included from main.c:23:
     m4.h:60: parse error before `malloc'
     m4.h:60: warning: data definition has no type or storage class
     m4.h:61: parse error before `realloc'
     m4.h:61: warning: data definition has no type or storage class
     main.c: In function `main':
     main.c:239: `STDIN_FILENO' undeclared (first use in this function)
     main.c:239: (Each undeclared identifier is reported only once
     main.c:239: for each function it appears in.)
     main.c:367: `PACKAGE' undeclared (first use in this function)
     main.c:367: `VERSION' undeclared (first use in this function)
     In file included from freeze.c:23:
     m4.h:60: parse error before `malloc'
     m4.h:60: warning: data definition has no type or storage class
     m4.h:61: parse error before `realloc'
     m4.h:61: warning: data definition has no type or storage class
     freeze.c: In function `produce_frozen_state':
     freeze.c:205: `PACKAGE' undeclared (first use in this function)
     freeze.c:205: (Each undeclared identifier is reported only once
     freeze.c:205: for each function it appears in.)
     freeze.c:205: `VERSION' undeclared (first use in this function)
     In file included from stackovf.c:80:
     m4.h:60: parse error before `malloc'
     m4.h:60: warning: data definition has no type or storage class
     m4.h:61: parse error before `realloc'
     m4.h:61: warning: data definition has no type or storage class
     $
     

The reason is that a number of symbols - such as STDIN_FILENO and VERSION have not been resolved; they were not found in any of the header files that we specified using -I. This is because we'll actually reslove these symbols in the last stage (linking) by including the relevant libraries. Despite these errors, we now have a collection of .s files:

     $ ls -l *.s
     -rw-r--r--   1 rich     users       44080 Sep 30 18:25 freeze.s
     -rw-r--r--   1 rich     users       20096 Sep 30 18:25 main.s
     -rw-r--r--   1 rich     users         810 Sep 30 18:25 stackovf.s
     -rw-r--r--   1 rich     users         949 Sep 30 18:25 temp.s
     $