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The one final complication is that I want you to include directives
to the assembler that will enable it to pass enough information about
your source program on to the interpreter to make symbolic debugging
of the original Co program possible. The format of these directives,
named STAB directives (for Symbol TABle), is described in the
assembler handout. However, I have tried to make it possible for
you to include these directives in your output without learning
much about their format (and without writing much code).
To do this, I will give you yet another file of C code, stabgen.c
and a new version of main.c. The new version of main.c differs from the
old one in that it assumes you will give it a file name to read Co
source code. This
is important, because it enables your compiler to tell the assembler
(and ultimately the interpreter) where the Co source code can be found.
This is done by including an STAB-FILE directive at the start of
your output file. The new main.c arranges to output this
directive by calling one of the routines provided in stabgen.c.
I have given you the source code for stabgen.c, but I suspect
you will not have to modify it. Nevertheless, you should make your
own copy of this source file and add its name to the SRC
line of your Makefile. It contains two routines that should provide
you with an easy way to output all the STAB directives required.
The procedure outputmainstabs should be called just before
you begin generating code for the main program. It expects a pointer
to the root of the program syntax tree as its operand. It will print
STAB directives describing all the types and global variables used in
the compiled program. Obviously, it depends on your symbol table structures
to determine this information.
The procedure outputprocstabs should be called once for each
procedure in the source program just before you begin to generate code
for that procedure. It expects a pointer to the Nprocdefn or
Nfuncdefn node for the procedure as a parameter. It outputs
STAB directives for all the parameters and locals of the procedure.
In addition to enabling the interpreter to provide debugging facilities
for your Co programs, it is hoped that the somewhat readable nature
of the STAB directives will make them useful when examining your compiler's
output. In particular, for each variable, these directives
provide a way to determine the displacement your compiler assigned to
the variable. Thus, to some degree, they can replace the
DumpDclDescs output.
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