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* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* This source file is part of SableVM. *
* *
* See the file "LICENSE" for the copyright information and for *
* the terms and conditions for copying, distribution and *
* modification of this source file. *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
m4 macros in SableVM
====================
SableVM provides a set of powerful m4 macros. This document describes
their usage, problems that may occur, and walks through the
complexities of instructions_preparation.m4.c. More documentation can
be found in ./src/libsablevm/macros.m4
Mixed C and m4 files
====================
Oftentimes it may be convenient to have m4 macros inside certain
portions of a C file. Here is an easy way to convert from .c/.h to
.m4.c/.m4.h
If you change a file like this, you need to change Makefile.am to
build it properly. This is relatively easy, and there are many
examples to follow. You should also use
'svn mv <filename>.c <filename>.m4.c'
so that the file keeps sandbox history. Then, make sure the file
follows this format, defining macros wherever you need them:
/* m4svm_file_name */ <---- 1st line of file
/* m4svm_on(0)m4_dnl */
<< ordinary C code >>
/* some comment *[::]/
m4svm_off ();
*/
m4svm_define_begin v = ":], [:m4svm_macro_name:])";
<< C macro body here >>
m4svm_define_end v = ":])";
/* m4svm_macro_name(arg1,arg2,...,argN)
m4_undefine([:m4svm_macro_name:])
m4svm_on(0)m4_dnl */
<< more ordinary C code >>
EOF
C comments with commas inside macro bodies
==========================================
If you have C comments in a macro body, you cannot put a `,' inside
them. Rather, you must quote them using the redefined quote tokens, like so:
[:,:]
Usually it's easier just to write the C comments without commas in the
first place.
Mismatched C parentheses in a macro body
========================================
If for some reason you have mismatched parentheses in a macro body,
this will confuse m4 even if the mismatch is only relevant to the
generated C code. You might think it is an m4 bug when really it's
the C code that's at fault.
Maximum macro body length
=========================
At some point, while writing a long instruction in instructions.m4.c,
I came across a maximum where m4 would no longer recognize the
m4svm_instruction_tail() macro properly. If you have really long
macro bodies (500+ lines), and are getting confusing m4 errors, try
cutting down the size of the macro body.
Details on instructions_preparation.m4.c
========================================
Here we'll cover m4svm_instruction_1, m4svm_instruction_2$1, and the
rest of the stuff in ./src/libsablevm/instructions_preparation.m4.c
The problem is that GNU indent puts a space between the function and
the left parenthesis, e.g. 'foo (arg1, arg2);'. Unfortunately m4 does
not allow for a space between the parenthesis and the macro name. So,
we have to play tricks. :-) Let's do it in steps.
STEP 1.
m4svm_instruction_head (NOP, SVM_INTRP_FLAG_INLINEABLE, 0);
expands to:
m4svm_instruction_1( (NOP, SVM_INTRP_FLAG_INLINEABLE, 0);
<< instruction body in C >>
m4svm_instruction_tail ();
Now,
m4svm_instruction_tail
expands to:
))m4_dnl ();
This whole thing (after applying m4_dnl) becomes:
m4svm_instruction_1( (NOP, SVM_INTRP_FLAG_INLINEABLE, 0);
<< instruction body in C >>
))
STEP 2.
The above result becomes a call to m4svm_instruction_1 with a single
parameter [delimited by parentheses]. The argument is:
(NOP, SVM_INTRP_FLAG_INLINEABLE, 0);
<< instruction body in C >>
)
STEP 3.
m4svm_instruction_1 is expanded and we get:
m4svm_instruction_2(NOP, SVM_INTRP_FLAG_INLINEABLE, 0);
Which ends with a ";", and it does not include the instruction body.
So, we must expand m4svm_instruction_2.
STEP 4.
m4svm_instruction_2(NOP, SVM_INTRP_FLAG_INLINEABLE, 0);
expands to:
m4svm_instruction($1, $2, $3,m4_dnl
or, more precisely:
m4svm_instruction(NOP, SVM_INTRP_FLAG_INLINEABLE, 0,m4_dnl;
So, after applying m4_dnl, the whole thing now looks as:
m4svm_instruction(NOP, SVM_INTRP_FLAG_INLINEABLE, 0,
<< instruction body in C >>
)
Which also gets rid of the ";" at the end of the
m4svm_instruction_head line. Now m4svm_instruction has all the
params that we wanted it to have.
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