10.12. Linker Example

This example links three object files named demo.c.o, ctrl.c.o, and tables.c.o and creates a program called demo.out.

Assume that target memory has the following program memory configuration:

Address Range	Contents
0x00000000 to 0x00001000	SLOW_MEM
0x00001000 to 0x00002000	FAST_MEM
0x08000000 to 0x08000400	EEPROM

The output sections are constructed in the following manner:

• Executable code, contained in the .text sections of demo.c.o, ctrl.c.o, and tables.c.o, must be linked into FAST_MEM.

• A set of interrupt vectors, contained in the .intvecs section of tables.c.o, must be linked at address FAST_MEM.

• A table of coefficients, contained in the .data section of tables.c.o, must be linked into EEPROM. The remainder of block FLASH must be initialized to the value 0xFF00FF00.

• A set of variables, contained in the .bss section of ctrl.c.o, must be linked into SLOW_MEM and preinitialized to 0x00000100.

• The .bss sections of demo.c.o and tables.c.o must be linked into SLOW_MEM.

The following example shows the linker command file for this example. After the linker command file, the map file is shown.

/*****************************************************************************/
/*** Specify Link Options ***/
/*****************************************************************************/
--entry_point SETUP /* Define the program entry point */
--output_file=demo.out /* Name the output file */
--map_file=demo.map /* Create an output map file */
/*****************************************************************************/
/*** Specify the Input Files ***/
/*****************************************************************************/
demo.c.o
ctrl.c.o
tables.c.o
/*****************************************************************************/
/*** Specify the Memory Configurations ***/
/*****************************************************************************/
MEMORY
{
    FAST_MEM : org = 0x00000000 len = 0x00001000 /* PROGRAM MEMORY (ROM) */
    SLOW_MEM : org = 0x00001000 len = 0x00001000 /* DATA MEMORY (RAM) */
    EEPROM : org = 0x08000000 len = 0x00000400 /* COEFFICIENTS (EEPROM) */
}
/*****************************************************************************/
/* Specify the Output Sections */
/*****************************************************************************/
SECTIONS
{
    .text : {} > FAST_MEM /* Link all .text sections into ROM */
    .intvecs : {} > 0x0 /* Link interrupt vectors at 0x0 */
    .data : /* Link .data sections */
    {
        tables.c.o(.data)
        . = 0x400; /* Create hole at end of block */
    } > EEPROM, fill = 0xFF00FF00 /* Fill and link into EEPROM */
    ctrl_vars: /* Create new sections for ctrl variables */
    {
        ctrl.c.o(.bss)
    } > SLOW_MEM, fill = 0x00000100 /* Fill with 0x100 and link into RAM */
    .bss : {} > SLOW_MEM /* Link remaining .bss sections into RAM */
}
/*****************************************************************************/
/*** End of Command File ***/
/*****************************************************************************/

Invoke the linker by entering the following command:

tiarmclang demo.cmd

This creates the following map file and an output file called demo.out that can be run on an Arm device.

OUTPUT FILE NAME:   <demo.out>
ENTRY POINT SYMBOL: "SETUP"  address: 000000d4
MEMORY CONFIGURATION

name      origin     length     attributes     fill
--------   --------   ---------   ----------   --------
FAST_MEM   00000000   000001000      RWIX
SLOW_MEM   00001000   000001000      RWIX
EEPROM     08000000   000000400      RWIX

SECTION ALLOCATION MAP

output                                      attributes/
section   page    origin      length       input sections
--------  ----  ----------  ----------    ----------------
.text      0    00000020    00000138
                  00000020    000000a0     ctrl.c.o (.text)
                  000000c0    00000000     tables.c.o (.text)
                  000000c0    00000098     demo.c.o (.text)

.intvecs   0    00000000    00000020
                   00000000    00000020     tables.c.o (.intvecs)

.data      0    08000000    00000400
                  08000000    00000168     tables.c.o (.data)
                  08000168    00000298     --HOLE-- [fill = ff00ff00]
                  08000400    00000000     ctrl.c.o (.data)
                  08000400    00000000     demo.c.o (.data)

ctrl_var   0    00001000    00000500
                  00001000    00000500     ctrl.c.o (.bss) [fill = 00000100]

.bss       0    00001500    00000100     UNINITIALIZED
                  00001500    00000100     demo.c.o (.bss)
                  00001600    00000000     tables.c.o (.bss)

GLOBAL SYMBOLS
address  name                             address  name
-------- ----                             -------- ----
000000d4 SETUP                            00000020 clear
00000020 clear                            000000b8 set
000000b8 set                              000000c0 x42
000000c0 x42                              000000d4 SETUP

[4 symbols]