   About the Generated C Code

   People  who  want  or  have  to code part of their applications and/or
   libraries  in C should really limit themselves to the clean interfaces
   provided  by [1]Cecil or the [2]external mechanism. This page mentions
   some facts you should be aware of before you start.

   Generated Type Identifiers

   First   and  above  all,  SmartEiffel  generates  one  unique  numeric
   identifier  for each living type[3]1 present in the Eiffel code. A lot
   of symbols in the generated C code depend on that identifier.

   Don't  depend  on  those identifiers! The mangling table is only valid
   for  one  specific  compilation  of  one specific application with one
   specific compiler version and specific libraries...

   If xyz is the identifier, then:
     * The type of an Eiffel object is Txyz;
     * The  corresponding structure is Sxyz; in that structure, the names
       of  the  attributes  are prefixed with an underscore (there may be
       some  other fields, usually the first being id used by SmartEiffel
       for bookkeeping);
     * Each reference type can be cast in T0 (but some reference type may
       not have the id field):

typedef int Tid;
typedef struct S0 T0;
struct S0{Tid id;};

     * Each method is named rxyzmethodname();
     * Each prefix method is named rxyz_px_methodname();
     * Each infix method is named rxyz_ix_methodname();
     * Each late-binding method is named Xxyzmethodname();
     * The creation procedures (which exist only if the Garbage Collector
       is used) are named newxyz().
     * The  model for objects of type xyz are named Mxyz. Models are used
       for initialisation. Example:

T132 M132={132,NULL,NULL,0,0,NULL,0,0,0,0,0,0,0,0,0,NULL};
...
{T132*n=((T132*)se_malloc(sizeof(*n)));
*n=M132;
r132make(n);
...

   Some  characters  in  method names such as "<" or "+" will be replaced
   with relative ASCII number written as decimal.

   For example: STRING has the indentifier 7[4]2. Then:
     * The object type is T7

typedef struct S7 T7;

     * The structure may be defined in S7

struct S7{Tid id;T9 _storage;T2 _count;T2 _capacity;};

     * The append is defined like this:

void r7append(se_dump_stack*caller,T7* C,T0* a1);

       (more on the dump stack below)

   When you compile your application, you can find those identifiers in a
   file  name after the name of the root class, suffixed by .id; the file
   is  structured in entries, each entry being separated from others by a
   hash character ('#'). This file looks like this:

4 "REAL"
#
12 "HELLO_WORLD"
class-path: "./hello_world.e"
class-name: HELLO_WORLD
parent-count: 0
c-type: T12 reference: yes
ref-status: live id-field: yes
run-time-set-count: 1
run-time-set:
        HELLO_WORLD (12)
#
9 "NATIVE_ARRAY[CHARACTER]"
class-path: "/lib/se/lib/kernel/native_array.e"
class-name: NATIVE_ARRAY
parent-count: 1 parents: 26
c-type: T9 reference: no
#
21 "COMPARABLE"
class-path: "/lib/se/lib/kernel/comparable.e"
class-name: COMPARABLE
parent-count: 1 parents: 13
#
. . .

   You must not depend on the indentifiers values. Indeed, when computing
   an  identifier,  collisions  may occur, and affect this process. Thus,
   the  number  (and name) corresponding to each type depends not only on
   the  type name, but also on the order in which they are compiled. That
   is,  on  the application and libraries compiled... They also depend on
   the  compilation  mode  used,  and  the version of the compiler you're
   using.  So  what  is  T145  now  may  become  T234  the  next time you
   compile...[5]3

   Consequently,  do not, ever, rely on the type numbers in the generated
   C  code,  because  they are not constant! (Except for a few ones which
   have  a fixed, hard-coded name). So don't bother writing in your own C
   code  things  such  as  new123  or  T456,  because  the  only thing we
   guarantee in this case is that your code shall break someday.

   The Naming Convention

   The previous chapter explains how method names are generated. r7append
   prototype  presented  above  as void r7append(se_dump_stack*caller,T7*
   C,T0* a1); shows Current and argument cases. Rules are as follow:
     * Current   is   named   C   when   given   as   parameter   to  the
       procedure/function.  This  parameter  may be omitted if Current is
       not  used.  In  some  cases (when inlining is done in boost mode),
       Current is copied in local variables named C1, C2...
     * Arguments are named a1, a2...
     * Inside functions, a local variable named R is defined. This is the
       Result value.
     * Local  variables  names  are Eiffel names prefixed with underscore
       character.

   The Mangling Table

   OK,  so  now  you  understand why you cannot use type numbers, but you
   still want to know what those things in the mangling table mean. :-)

   First,  a  big  caveat.  Although it hasn't changed a lot and has been
   very  stable  for  quite  some time now, the mangling table coding may
   change  in the future! We currently have no plans to change it, and we
   prefer  keeping  it  the  way  it is. But once again, we do not commit
   ourselves to the current representation.

   Let's  look  again at the extract of a .id file. The shown part covers
   quite all the possible cases:

4 "REAL"
#
12 "HELLO_WORLD"
class-path: "./hello_world.e"
class-name: HELLO_WORLD
parent-count: 0
c-type: T12 reference: yes
ref-status: live id-field: yes
run-time-set-count: 1
run-time-set:
        HELLO_WORLD (12)
#
9 "NATIVE_ARRAY[CHARACTER]"
class-path: "/lib/se/lib/kernel/native_array.e"
class-name: NATIVE_ARRAY
parent-count: 1 parents: 26
c-type: T9 reference: no
#
21 "COMPARABLE"
class-path: "/lib/se/lib/kernel/comparable.e"
class-name: COMPARABLE
parent-count: 1 parents: 13
#
. . .

   There  is  one  entry per type (live or not); each entry spans on many
   lines and finished by a hash symbol ('#').

   Each  entry  comprises  many  informations. All of them are not always
   present  (in that case, they have default values). Only the first line
   is compulsory.

   The first line contains the type number, and its name (as would return
   generating_type).

   The  next lines contain different fields, marked as a keyword, a colon
   and a value. There may be one or more fields on one line. Those fields
   are:

   class-path The path to the file containing the source of the class.
   May be omitted if the class has no associated file (e.g., TUPLE or
   PROCEDURE).
   class-name The name of the class, as would return generator.
   parent-count The number of parents.
   parents On the same line as parent-count if the latter is not null; it
   gives the parent class identifiers.
   c-type The C type, usually in the form Txyz. If omitted, the class has
   no runnable type.
   In that case, the following fields do not appear either.
   reference On the same line as c-type, yes for a reference type or no
   for an expanded type.
   ref-status Either live for a living type (i.e. whether instances of
   this type are ever created at run-time), or dead otherwise.
   id-field On the same line as ref-status, yes if the id field is in the
   generated C structure (as its first element), no otherwise. This field
   is present if one of these confitions is true:
     * some late binding may occur on targets of that type,
     * or the struct may be accessed by external or Cecil code.

   Note that a lot of calls are statically computed; the type inference
   algorithm used in SmartEiffel increases the number of such types that
   don't need the id field.
   run-time-set-count  The  number  of  concrete, live descendants of the
   type  (including  itself).  It  is  thus  the  number  of items in the
   run-time-set below.
   run-time-set  Contains  the live heirs with their identifier. There is
   one such class per line.

   The Dump Stack

   When not in boost mode, a stack is managed by the SmartEiffel runtime.
   This stack can be displayed when an exception not caught is raised. It
   is also used by the debugger ([6]sedb).

   Technically, the SmartEiffel stack is built upon the native (C) stack.
   It  is  a se_dump_stack[7]4 usually allocated on the stack. It is made
   up of several parts:
     * a  frame  descriptor,  of  type se_frame_descriptor[8]4 which is a
       static  description of the feature: run type, does it use Current,
       number  and  type  of the locals (parameters and local variables),
       and an anti-recursion flag (when testing contracts);
     * a pointer to Current (i.e. either a pointer to an expanded object,
       or  a  pointer  to  a  reference object, it being a pointer to the
       object  itself).  That's  why  the  type  of  the current field is
       Void**.  This  field  will  be  NULL if Current is not used by the
       feature;
     * the position (used mainly by [9]sedb);
     * a  pointer  to  the  caller (i.e. the se_dump_stack of the calling
       function);
     * a pointer to the exception origin: if not NULL, it means that this
       se_dump_stack  is  not in the stack, but was malloc'ed to preserve
       the exception stack trace;
     * an array of locals (with double indirection as for Current), hence
       the type void***.

   One  macro  handles the linking and unlinking of the dump stack frames
   by  setting the caller field of the dump stack top, then changing that
   top.
     * Normally,  the  dump  stack  top  is  a  global  se_dst defined in
       SmartEiffel/sys/runtime/no_check.c.  The  set_dump_stack_top  just
       affects the given argument to se_dst.
     * In SCOOP mode, things are a bit different since each processor has
       its own stack. set_dump_stack_top has two arguments: the processor
       and the new dump stack top.

   The Basic Subsystem

   That "basic" subsystem is used by SmartEiffel libraries to provide, at
   the same time, facility of extension and independance from the backend
   (C, Java).

   Features  named basic_something and declared as external "SmartEiffel"
   are handled by the basic subsystem.

   The naming scheme is thus:
feature

   basic_topic_my_feature(args) is
      external "SmartEiffel"
      end

   The   C   backend[10]5   will   then   search  for  basic_topic.c  and
   basic_topic.h  (those found will be included in good place, one in the
   generated  .c,  other  in  the  .h).  In those files, a function (or a
   macro)   must  be  named  basic_topic_my_feature()  (like  the  Eiffel
   feature),  and  accept  the  same  arguments as its Eiffel counterpart
   (that is, written the C way). Current is never passed.

   Indeed  this  is  a  kind  of  "plugin"  system  for  the  SmartEiffel
   libraries. Some extensions may be foreseen in the future.

   For some examples, one may look at BASIC_DIRECTORY and so on.

   Notes

   [11]1

     There  is  a bijection between the number and the name of the type,
     including  its parameters in the case of generic types. (My_Feature
     details about this in our [12]research papers).

   [13]2

     There  are  some  identifiers  that are reserved for "basic" types.
     They are:
     * 0 is the type any other can cast to;
     * 1 is INTEGER_8;
     * 2 is INTEGER_32;
     * 3 is CHARACTER;
     * 4 is REAL;
     * 5 is DOUBLE;
     * 6 is BOOLEAN;
     * 7 is STRING;
     * 8 is POINTER;
     * 9 is NATIVE_ARRAY[CHARACTER] (used by STRING);
     * 10 is INTEGER_16;
     * 11 is INTEGER_64.

     The  root  class of the system will then have the 12. Don't rely on
     that, though (before all those INTEGERs revolution, it was 11).

   [14]3

     The  compiler  will  do  its  best  not  to  change the identifiers
     uselessly.  The  .id  file  is  loaded  at  the  beginning  of  the
     compilation  process,  and saved again at its end. But clean erases
     that file.

   [15]4

     You   may   find   the   definition  of  those  structures  in  the
     SmartEiffel/sys/runtime/c/no_check.h file.

   [16]5

     The   Java   backend   is   similar.   It   looks   for  the  class
     fr.loria.SmartEiffelBasicTopic     and    the    static    function
     basic_topic_my_feature()  with the arguments quite similar to the C
     ones.

                                   [Line]
             Copyright © Dominique COLNET and Suzanne COLLIN -
                         [17]<SmartEiffel@loria.fr>
                Last modified: Thu Jun 12 10:50:08 CEST 2003

References

   1. file://localhost/users/miro/colnet/SmartEiffel/man/cecil.html
   2. file://localhost/users/miro/colnet/SmartEiffel/man/external.html
   3. file://localhost/users/miro/colnet/SmartEiffel/man/c_code.html#note1
   4. file://localhost/users/miro/colnet/SmartEiffel/man/c_code.html#note2
   5. file://localhost/users/miro/colnet/SmartEiffel/man/c_code.html#note3
   6. file://localhost/users/miro/colnet/SmartEiffel/man/sedb.html
   7. file://localhost/users/miro/colnet/SmartEiffel/man/c_code.html#note4
   8. file://localhost/users/miro/colnet/SmartEiffel/man/c_code.html#note4
   9. file://localhost/users/miro/colnet/SmartEiffel/man/sedb.html
  10. file://localhost/users/miro/colnet/SmartEiffel/man/c_code.html#note5
  11. file://localhost/users/miro/colnet/SmartEiffel/man/c_code.html#ref_note1
  12. file://localhost/users/miro/colnet/SmartEiffel/papers/papers.html
  13. file://localhost/users/miro/colnet/SmartEiffel/man/c_code.html#ref_note2
  14. file://localhost/users/miro/colnet/SmartEiffel/man/c_code.html#ref_note3
  15. file://localhost/users/miro/colnet/SmartEiffel/man/c_code.html#ref_note4
  16. file://localhost/users/miro/colnet/SmartEiffel/man/c_code.html#ref_note5
  17. mailto:SmartEiffel@loria.fr
