paj@hic.uucp (Paul Johnson) (03/22/90)
I have been using gcc for Eiffel C compilation, and am posting my
experiences for the benefit of the net (along with a query):
As it says in the Environment manual, set the environment variables
"C_COMPILER" and "LINK_EDITOR" to the compiler plus command line
arguments. The arguments I am currently using are:
-g
I know about not using dbx to debug Eiffel, but once in a
while I get a segmentation violation, and dbx is the easiest
way to find out what has gone wrong.
-traditional
If you have a look at the "Incompatabilities" section of the
GCC manual, it lists a lot of little things which are changed
back by this flag. Whether any of them matter is a good
question. The differences are:
- Quoted macro argument substitution.
- Rregister allocation in routines using setjmp (Eiffel uses
setjmp for exception handling: see "_eiffel.h").
- extern funtion scope.
- Unterminated character strings in failed #if constructs are
caught.
- Float/double parameter conversions.
-fpcc-struct-return
This tells gcc to return structures and unions in the same way
as most C compilers. This involves putting the structure in a
static buffer and returning a pointer to it. Gcc functions
take an implicit argument pointing to the eventual destination
of the result. This is both faster and reentrant.
This may affect programs with modules compiled under a mixture
of gcc and cc. The effect on external functions which return
stuructures is uncertain. According to the Eiffel environment
manual section 25.4, Eiffel expects such functions to behave
in the classic cc way. Whether the generated C which calls the
function is declared as receiving a pointer or a structure I
do not know.
-fwritable-strings
Gcc compiles string constants into the text area (read only).
This causes the "OnceStr" function in _basic.c to fail since
it puts Eiffel string header stuff in the first 8 bytes of the
string (the C version of the string has 8 leading asterisks).
This flag tells gcc to behave in the standard way.
If you do use gcc on your site, beware the dangers of mixed
compilation. I THINK the only way this will bite is in the structure
return problem described above (which only occurs when getting an
expanded class or "BITS M" type back anyway). Remember that Eiffel
".E" directories and the .o files in them are shared between all
users, so if there are any other problems or if you want to dispense
with the -fpcc-struct-return flag, then everyone on your installation
will have to use the same C compiler all the time.
For the record, we are using gcc version 1.35.
My query is: do any of the items in -traditional matter, or can we
dispense with that flag?
Disclaimer: These are personal opinions. If you want to try out the
ideas in this posting, you do so at your own risk.
Paul Johnson UUCP: <world>!mcvax!ukc!gec-mrc!paj
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