D Application Binary Interface
A D implementation that conforms to the D ABI (Application Binary Interface) will be able to generate libraries, DLL's, etc., that can interoperate with D binaries built by other implementations.
Most of this specification remains TBD (To Be Defined).
C ABI
The C ABI referred to in this specification means the C Application Binary Interface of the target system. C and D code should be freely linkable together, in particular, D code shall have access to the entire C ABI runtime library.
Basic Types
TBD
Structs
Conforms to the target's C ABI struct layout.
Classes
An object consists of:
| offset | contents |
|---|---|
| 0 | pointer to vtable |
| 4 | monitor |
| 8... | non-static members |
The vtable consists of:
| offset | contents |
|---|---|
| 0 | pointer to instance of ClassInfo |
| 4... | pointers to virtual member functions |
The class definition:
class XXXX
{
....
};
Generates the following:
- An instance of Class called ClassXXXX.
- A type called StaticClassXXXX which defines all the static members.
- An instance of StaticClassXXXX called StaticXXXX for the static members.
Interfaces
TBD
Arrays
A dynamic array consists of:
| offset | contents |
|---|---|
| 0 | array dimension |
| 4 | pointer to array data |
A dynamic array is declared as:
type[] array;whereas a static array is declared as:
type[dimension] array;Thus, a static array always has the dimension statically available as part of the type, and so it is implemented like in C. Static array's and Dynamic arrays can be easily converted back and forth to each other.
Associative Arrays
Associative arrays consist of a pointer to an opaque, implementation defined type. The current implementation is contained in phobos/internal/aaA.d.
Reference Types
D has reference types, but they are implicit. For example, classes are always referred to by reference; this means that class instances can never reside on the stack or be passed as function parameters.When passing a static array to a function, the result, although declared as a static array, will actually be a reference to a static array. For example:
int[3] abc;
Passing abc to functions results in these implicit conversions:
void func(int[3] array); // actually <reference to><array[3] of><int> void func(int* p); // abc is converted to a pointer // to the first element void func(int[] array); // abc is converted to a dynamic array
Name Mangling
D accomplishes typesafe linking by mangling a D identifier to include scope and type information.
MangledName:
_D QualifiedName Type
_D QualifiedName M Type
QualifiedName:
SymbolName
SymbolName QualifiedName
SymbolName:
LName
TemplateInstanceName
The M means that the symbol is a function that requires a this pointer.
Template Instance Names have the types and values of its parameters encoded into it:
TemplateInstanceName:
__T LName TemplateArgs Z
TemplateArgs:
TemplateArg
TemplateArg TemplateArgs
TemplateArg:
T Type
V Type Value
S LName
Value:
n
Number
N Number
e HexFloat
c HexFloat c HexFloat
HexFloat:
NAN
INF
NINF
N HexDigits P Exponent
HexDigits P Exponent
Exponent:
N Number
Number
HexDigits:
HexDigit
HexDigit HexDigits
HexDigit:
Digit
A
B
C
D
E
F
- n
- is for null arguments.
- Number
- is for positive numeric literals (including character literals).
- N Number
- is for negative numeric literals.
- e HexFloat
- is for real and imaginary floating point literals.
- c HexFloat c HexFloat
- is for complex floating point literals.
- Width Number _ HexDigits
- Width is whether the characters are 1 byte (a), 2 bytes (w) or 4 bytes (d) in size. Number is the number of characters in the string. The HexDigits are the hex data for the string.
Name:
Namestart
Namestart Namechars
Namestart:
_
Alpha
Namechar:
Namestart
Digit
Namechars:
Namechar
Namechar Namechars
A Name is a standard D identifier.
LName:
Number Name
Number:
Digit
Digit Number
Digit:
0
1
2
3
4
5
6
7
8
9
An LName is a name preceded by a Number giving the number of characters in the Name.
Type Mangling
Types are mangled using a simple linear scheme:
Type:
TypeArray
TypeSarray
TypeAarray
TypePointer
TypeFunction
TypeIdent
TypeClass
TypeStruct
TypeEnum
TypeTypedef
TypeDelegate
TypeNone
TypeVoid
TypeByte
TypeUbyte
TypeShort
TypeUshort
TypeInt
TypeUint
TypeLong
TypeUlong
TypeFloat
TypeDouble
TypeReal
TypeIfloat
TypeIdouble
TypeIreal
TypeCfloat
TypeCdouble
TypeCreal
TypeBool
TypeChar
TypeWchar
TypeDchar
TypeTuple
TypeArray:
A Type
TypeSarray:
G Number Type
TypeAarray:
H Type Type
TypePointer:
P Type
TypeFunction:
CallConvention Arguments ArgClose Type
CallConvention:
F
U
W
V
R
Arguments:
Argument
Argument Arguments
Argument:
Type
J Type
K Type
L Type
ArgClose
X
Y
Z
TypeIdent:
I LName
TypeClass:
C LName
TypeStruct:
S LName
TypeEnum:
E LName
TypeTypedef:
T LName
TypeDelegate:
D TypeFunction
TypeNone:
n
TypeVoid:
v
TypeByte:
g
TypeUbyte:
h
TypeShort:
s
TypeUshort:
t
TypeInt:
i
TypeUint:
k
TypeLong:
l
TypeUlong:
m
TypeFloat:
f
TypeDouble:
d
TypeReal:
e
TypeIfloat:
o
TypeIdouble:
p
TypeIreal:
j
TypeCfloat:
q
TypeCdouble:
r
TypeCreal:
c
TypeBool:
b
TypeChar:
a
TypeWchar:
u
TypeDchar:
w
TypeTuple:
B Number Arguments
Function Calling Conventions
The extern (C) calling convention matches the C calling convention used by the supported C compiler on the host system. The extern (D) calling convention for x86 is described here.
Register Conventions
- EAX, ECX, EDX are scratch registers and can be destroyed by a function.
- EBX, ESI, EDI, EBP must be preserved across function calls.
- EFLAGS is assumed destroyed across function calls, except for the direction flag which must be forward.
- The FPU stack must be empty when calling a function.
- The FPU control word must be preserved across function calls.
- Floating point return values are returned on the FPU stack. These must be cleaned off by the caller, even if they are not used.
Return Value
- The types bool, byte, ubyte, short, ushort, int, uint, pointer, Object, and interfaces are returned in EAX.
- long and ulong are returned in EDX,EAX, where EDX gets the most significant half.
- float, double, real, ifloat, idouble, ireal are returned in ST0.
- cfloat, cdouble, creal are returned in ST1,ST0 where ST1 is the real part and ST0 is the imaginary part.
- Dynamic arrays are returned with the pointer in EDX and the length in EAX.
- Associative arrays are returned in EAX with garbage returned in EDX. The EDX value will probably be removed in the future; it's there for backwards compatibility with an earlier implementation of AA's.
- Delegates are returned with the pointer to the function in EDX and the context pointer in EAX.
- For Windows, 1, 2 and 4 byte structs are returned in EAX.
- For Windows, 8 byte structs are returned in EDX,EAX, where EDX gets the most significant half.
- For other struct sizes, and for all structs on Linux, the return value is stored through a hidden pointer passed as an argument to the function.
- Constructors return the this pointer in EAX.
Parameters
The parameters to the non-variadic function:
foo(a1, a2, ..., an);
are passed as follows:
| a1 |
| a2 |
| ... |
| an |
| hidden |
| this |
where hidden is present if needed to return a struct value, and this is present if needed as the this pointer for a member function or the context pointer for a nested function.
The last parameter is passed in EAX rather than being pushed on the stack if the following conditions are met:
- It fits in EAX.
- It is not a 3 byte struct.
Parameters are always pushed as multiples of 4 bytes, rounding upwards, so the stack is always aligned on 4 byte boundaries. They are pushed most significant first. out and inout are passed as pointers. Static arrays are passed as pointers to their first element. On Windows, a real is pushed as a 10 byte quantity, a creal is pushed as a 20 byte quantity. On Linux, a real is pushed as a 12 byte quantity, a creal is pushed as two 12 byte quantities. The extra two bytes of pad occupy the 'most significant' position.
The callee cleans the stack.
The parameters to the variadic function:
void foo(int p1, int p2, int[] p3...) foo(a1, a2, ..., an);
are passed as follows:
| p1 |
| p2 |
| a3 |
| hidden |
| this |
The variadic part is converted to a dynamic array and the rest is the same as for non-variadic functions.
The parameters to the variadic function:
void foo(int p1, int p2, ...) foo(a1, a2, a3, ..., an);
are passed as follows:
| an |
| ... |
| a3 |
| a2 |
| a1 |
| _arguments |
| hidden |
| this |
The caller is expected to clean the stack. _argptr is not passed, it is computed by the callee.