|
| #define | __attribute__(x) |
| |
| #define | __table(type, name) ( type, name ) |
| | Declare a linker table. More...
|
| |
| #define | __table_type(table) __table_extract_type table |
| | Get linker table data type. More...
|
| |
| #define | __table_extract_type(type, name) type |
| |
| #define | __table_name(table) __table_extract_name table |
| | Get linker table name. More...
|
| |
| #define | __table_extract_name(type, name) name |
| |
| #define | __table_section(table, idx) ".tbl." __table_name ( table ) "." __table_str ( idx ) |
| | Get linker table section name. More...
|
| |
| #define | __table_str(x) #x |
| |
| #define | __table_alignment(table) __alignof__ ( __table_type ( table ) ) |
| | Get linker table alignment. More...
|
| |
| #define | __table_entry(table, idx) |
| | Declare a linker table entry. More...
|
| |
| #define | __table_entries(table, idx) |
| | Get start of linker table entries. More...
|
| |
| #define | __TABLE_ENTRIES(entries, table, idx) |
| | Declare start of linker table entries. More...
|
| |
| #define | table_start(table) __table_entries ( table, 00 ) |
| | Get start of linker table. More...
|
| |
| #define | TABLE_START(start, table) __TABLE_ENTRIES ( start, table, 00 ) |
| | Declare start of linker table. More...
|
| |
| #define | table_end(table) __table_entries ( table, 99 ) |
| | Get end of linker table. More...
|
| |
| #define | TABLE_END(end, table) __TABLE_ENTRIES ( end, table, 99 ) |
| | Declare end of linker table. More...
|
| |
| #define | table_num_entries(table) |
| | Get number of entries in linker table. More...
|
| |
| #define | table_index(table, entry) ( ( unsigned int ) ( (entry) - table_start ( table ) ) ) |
| | Get index of entry within linker table. More...
|
| |
| #define | for_each_table_entry(pointer, table) |
| | Iterate through all entries within a linker table. More...
|
| |
| #define | for_each_table_entry_continue(pointer, table) |
| | Iterate through all remaining entries within a linker table. More...
|
| |
| #define | for_each_table_entry_reverse(pointer, table) |
| | Iterate through all entries within a linker table in reverse order. More...
|
| |
| #define | for_each_table_entry_continue_reverse(pointer, table) |
| | Iterate through all remaining entries within a linker table in reverse order. More...
|
| |
Linker tables.
Read #ifdef considered harmful first for some background on the motivation for using linker tables.
This file provides macros for dealing with linker-generated tables of fixed-size symbols. We make fairly extensive use of these in order to avoid #ifdef spaghetti and/or linker symbol pollution. For example, instead of having code such as
#ifdef CONSOLE_SERIAL
#endif
we make serial.c generate an entry in the initialisation function table, and then have a function call_init_fns() that simply calls all functions present in this table. If and only if serial.o gets linked in, then its initialisation function will be called. We avoid linker symbol pollution (i.e. always dragging in serial.o just because of a call to serial_init()) and we also avoid #ifdef spaghetti (having to conditionalise every reference to functions in serial.c).
The linker script takes care of assembling the tables for us. All our table sections have names of the format NAME designates the data structure stored in the table (e.g. init_fns) and NN is a two-digit decimal number used to impose an ordering upon the tables if required. NN=00 is reserved for the symbol indicating "table start", and NN=99 is reserved for the symbol indicating "table end".
As an example, suppose that we want to create a "frobnicator" feature framework, and allow for several independent modules to provide frobnicating services. Then we would create a frob.h header file containing e.g.
struct frobnicator {
void ( *frob ) ( void );
};
#define FROBNICATORS __table ( struct frobnicator, "frobnicators" )
#define __frobnicator __table_entry ( FROBNICATORS, 01 )
Any module providing frobnicating services would look something like
#include "frob.h"
static void my_frob ( void ) {
...
}
struct frob my_frobnicator __frobnicator = {
.name = "my_frob",
.frob = my_frob,
};
The central frobnicator code (frob.c) would use the frobnicating modules as follows
#include "frob.h"
void frob_all ( void ) {
struct frob *frob;
for_each_table ( frob, FROBNICATORS ) {
printf (
"Calling frobnicator \"%s\"\n", frob->name );
frob->frob ();
}
}
See init.h and init.c for a real-life example.
Definition in file tables.h.
