@ -32,14 +32,14 @@
*
* To accomodate this situation , the AST_OPTIONAL_API macro allows an API
* function to be declared in a special way , if Asterisk being built on a
* platform that supports the GCC ' weak ' and ' alias ' attributes . If so ,
* the API function is actually a weak symbol , which means if the provider
* the API is not loaded , the symbol can still be referenced ( unlike a
* platform that supports special compiler and dynamic linker attributes .
* If so the API function will actually be a weak symbol , which means if the
* provider of the API is not loaded , the symbol can still be referenced ( unlike a
* strong symbol , which would cause an immediate fault if not defined when
* referenced ) , but it will return NULL signifying the linker / loader was
* not able to resolve the symbol . In addition , the macro defines a hidden
* ' stub ' version of the API call , using a provided function body , and uses
* the alias attribute to make the API function symbol actually resolve to
* various methods to make the API function symbol actually resolve to
* that hidden stub , but only when the * real * provider of the symbol has
* not been found .
*
@ -57,13 +57,25 @@
* safely know that the API is not available , and to avoid using any
* other APIs from the not - present provider .
*
* In addition to this declaration in the header file , the actual definition of
* the API function must use the AST_OPTIONAL_API_NAME macro to ( possibly )
* modify the real name of the API function , depending on the specific
* implementation requirements . The corresponding example from res_agi . c :
*
* \ code
* int AST_OPTIONAL_API_NAME ( ast_agi_register ) ( struct ast_module * mod , agi_command * cmd )
* {
* . . .
* }
* \ endcode
*
* In the module providing the API , the AST_OPTIONAL_API macro must
* be informed that it should not build the hidden stub function or
* apply special aliases to the function prototype ; this can be done
* by defining AST_API_MODULE just before including the header file
* containing the AST_OPTIONAL_API macro calls .
*
* \ note If the GCC ' weak ' and ' alias ' attributes are not available ,
* \ note If the platform does not provide adequate resources ,
* then the AST_OPTIONAL_API macro will result in a non - optional function
* definition ; this means that any consumers of the API functions so
* defined will require that the provider of the API functions be
@ -83,17 +95,115 @@
*/
# define AST_OPTIONAL_API_UNAVAILABLE INT_MIN
# if defined(HAVE_ATTRIBUTE_weak_import) && !defined(AST_API_MODULE)
# define AST_OPTIONAL_API(result, name, proto, stub) result name proto __attribute__((weak_import));
# define AST_OPTIONAL_API_ATTR(result, attr, name, proto, stub) result name proto __attribute__((weak_import,attr));
# elif defined(HAVE_ATTRIBUTE_weak) && defined(HAVE_ATTRIBUTE_alias) && !defined(AST_API_MODULE) && !defined(HAVE_ATTRIBUTE_weak_import)
# define AST_OPTIONAL_API(result, name, proto, stub) \
static result __ # # name proto stub ; \
result __attribute__ ( ( weak , alias ( " __ " __stringify ( name ) ) ) ) name proto ;
# define AST_OPTIONAL_API_ATTR(result, attr, name, proto, stub) \
static result __attribute__ ( ( attr ) ) __ # # name proto stub ; \
result __attribute__ ( ( weak , alias ( " __ " __stringify ( name ) ) , attr ) ) name proto ;
# if defined(HAVE_ATTRIBUTE_weak_import)
/*
* This is the Darwin ( Mac OS / X ) implementation , that only provides the
* ' weak_import ' compiler attribute for weak symbols . On this platform ,
*
* - The module providing the API will only provide a ' __ ' prefixed version
* of the API function to other modules ( this will be hidden from the other
* modules by the macros ) , so any modules compiled against older versions
* of the module that provided a non - prefixed version of the API function
* will fail to link at runtime .
* - In the API module itself , access to the API function without using a
* prefixed name is provided by a static pointer variable that holds the
* function address .
* - ' Consumer ' modules of the API will use a combination of a weak_import
* symbol , a local stub function , a pointer variable and a constructor function
* ( which initializes that pointer variable as the module is being loaded )
* to provide safe , optional access to the API function without any special
* code being required .
*/
# define AST_OPTIONAL_API_NAME(name) __##name
# if defined(AST_API_MODULE)
# define AST_OPTIONAL_API(result, name, proto, stub) \
result AST_OPTIONAL_API_NAME ( name ) proto ; \
static attribute_unused typeof ( AST_OPTIONAL_API_NAME ( name ) ) * const name = AST_OPTIONAL_API_NAME ( name ) ;
# define AST_OPTIONAL_API_ATTR(result, attr, name, proto, stub) \
result __attribute__ ( ( attr ) ) AST_OPTIONAL_API_NAME ( name ) proto ; \
static attribute_unused typeof ( AST_OPTIONAL_API_NAME ( name ) ) * const name = AST_OPTIONAL_API_NAME ( name ) ;
# else
# define AST_OPTIONAL_API(result, name, proto, stub) \
static result __stub__ # # name proto stub ; \
__attribute__ ( ( weak_import ) ) typeof ( __stub__ # # name ) AST_OPTIONAL_API_NAME ( name ) ; \
static attribute_unused typeof ( __stub__ # # name ) * name ; \
static void __attribute__ ( ( constructor ) ) __init__ # # name ( void ) { name = AST_OPTIONAL_API_NAME ( name ) ? : __stub__ # # name ; }
# define AST_OPTIONAL_API_ATTR(result, attr, name, proto, stub) \
static __attribute__ ( ( attr ) ) result __stub__ # # name proto stub ; \
__attribute__ ( ( attr , weak_import ) ) typeof ( __stub__ # # name ) AST_OPTIONAL_API_NAME ( name ) ; \
static attribute_unused __attribute__ ( ( attr ) ) typeof ( __stub__ # # name ) * name ; \
static void __attribute__ ( ( constructor ) ) __init__ # # name ( void ) { name = AST_OPTIONAL_API_NAME ( name ) ? : __stub__ # # name ; }
# endif
/* End of Darwin (Mac OS/X) implementation */
# elif defined(HAVE_ATTRIBUTE_weakref)
/*
* This is the generic GCC implementation , used when the ' weakref '
* compiler attribute is available . On these platforms :
*
* - The module providing the API will provide a ' __ ' prefixed version
* of the API function to other modules ( this will be hidden from the other
* modules by the macros ) , and also a non - prefixed alias so that modules
* compiled against older versions of the module that provided a non - prefixed
* version of the API function will continue to link properly .
* - In the API module itself , access to the API function without using a
* prefixed name is provided by the non - prefixed alias described above .
* - ' Consumer ' modules of the API will use a combination of a weakref
* symbol , a local stub function , a pointer variable and a constructor function
* ( which initializes that pointer variable as the module is being loaded )
* to provide safe , optional access to the API function without any special
* code being required .
*/
# define AST_OPTIONAL_API_NAME(name) __##name
# if defined(AST_API_MODULE)
# define AST_OPTIONAL_API(result, name, proto, stub) \
result AST_OPTIONAL_API_NAME ( name ) proto ; \
__attribute__ ( ( alias ( __stringify ( AST_OPTIONAL_API_NAME ( name ) ) ) ) ) typeof ( AST_OPTIONAL_API_NAME ( name ) ) name ;
# define AST_OPTIONAL_API_ATTR(result, attr, name, proto, stub) \
result __attribute__ ( ( attr ) ) AST_OPTIONAL_API_NAME ( name ) proto ; \
__attribute__ ( ( alias ( __stringify ( AST_OPTIONAL_API_NAME ( name ) ) ) ) ) typeof ( AST_OPTIONAL_API_NAME ( name ) ) name ;
# else
# define AST_OPTIONAL_API(result, name, proto, stub) \
static result __stub__ # # name proto stub ; \
static __attribute__ ( ( weakref ( __stringify ( AST_OPTIONAL_API_NAME ( name ) ) ) ) ) typeof ( __stub__ # # name ) __ref__ # # name ; \
static attribute_unused typeof ( __stub__ # # name ) * name ; \
static void __attribute__ ( ( constructor ) ) __init__ # # name ( void ) { name = __ref__ # # name ? : __stub__ # # name ; }
# define AST_OPTIONAL_API_ATTR(result, attr, name, proto, stub) \
static __attribute__ ( ( attr ) ) result __stub__ # # name proto stub ; \
static __attribute__ ( ( attr , weakref ( __stringify ( AST_OPTIONAL_API_NAME ( name ) ) ) ) ) typeof ( __stub__ # # name ) __ref__ # # name ; \
static attribute_unused __attribute__ ( ( attr ) ) typeof ( __stub__ # # name ) * name ; \
static void __attribute__ ( ( constructor ) ) __init__ # # name ( void ) { name = __ref__ # # name ? : __stub__ # # name ; }
# endif
/* End of GCC implementation */
# else
/* This is the non-optional implementation. */
# define AST_OPTIONAL_API_NAME(name) name
/*!
* \ brief Define an optional API function
*
@ -108,7 +218,8 @@
* { return AST_OPTIONAL_API_UNAVAILABLE ; } ) ;
* \ endcode
*/
# define AST_OPTIONAL_API(result, name, proto, stub) result name proto;
# define AST_OPTIONAL_API(result, name, proto, stub) result AST_OPTIONAL_API_NAME(name) proto
/*!
* \ brief Define an optional API function with compiler attributes
*
@ -118,7 +229,10 @@
* \ param proto The prototype ( arguments ) of the function
* \ param stub The code block that will be used by the hidden stub when needed
*/
# define AST_OPTIONAL_API_ATTR(result, attr, name, proto, stub) result __attribute__((attr)) name proto;
# define AST_OPTIONAL_API_ATTR(result, attr, name, proto, stub) result __attribute__((attr)) AST_OPTIONAL_API_NAME(name) proto
/* End of non-optional implementation */
# endif
# undef AST_API_MODULE
Kevin P. Fleming
16 years ago