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About the Generated C Code
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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
Cecil or the external
mechanism. This page mentions some facts you should be aware of before you start.
First and above all, SmartEiffel generates one unique numeric identifier for
each living type1 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 identifier 72.
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 identifiers 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...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 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.
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).
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class-name |
The name of the class, as would return generator.
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parent-count |
The number of parents.
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parents |
On the same line as parent-count if the latter is not null; it gives
the parent class identifiers.
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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.
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reference |
On the same line as c-type, yes for a reference type or
no for an expanded type.
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ref-status |
Either live for a living type (i.e. whether instances of this type
are ever created at run-time), or dead otherwise.
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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.
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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.
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run-time-set |
Contains the live heirs with their identifier. There is one such class per
line.
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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 (sedb).
Technically, the SmartEiffel stack is built upon the native (C) stack. It is a
se_dump_stack4 usually allocated on the
stack. It is made up of several parts:
- a frame descriptor, of type se_frame_descriptor4 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 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.
That "plugin" subsystem is used by SmartEiffel libraries to provide, at the
same time, facility of extension and independance from the backend (C, Java).
Features declared as external "plug_in" are handled
by the plugin subsystem. They must have an alias with the following informations:
- location: the location of the plug_in source (may depend on
environment variables, even those provided by the configuration
file---more details here).
- module_name: the name or the plugin. For a C plugin, it is
the name of the C files (without the
.c or
.h extensions). For a Java plugin, this system is not
yet supported (indeed compile_to_jvm will surely not ship
with 2.0, but should resurect like the Phoenix in a later version).
- feature_name: the name of the C (or Java) function to
call.
The naming scheme is thus:
feature
my_plugin_feature(args) is
external "plug_in"
alias "{
location: "${my_plugin}"
module_name: "myplug"
feature_name: "feature"
}"
end
The C backend will then search for myplug.c and
myplug.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 feature(), and accept
the same arguments as its Eiffel counterpart (that is, written the C
way). Note: Current is never passed.
For some examples, one may look at BASIC_DIRECTORY and so on.
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 research papers).
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).
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.
4 You may
find the definition of those structures in the
SmartEiffel/sys/runtime/c/no_check.h file.
Copyright © Dominique COLNET and Suzanne COLLIN -
<SmartEiffel@loria.fr>
Last modified: Thu Jun 12 10:50:08 CEST 2003
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