section ("section-name")

Normally, the compiler places the objects it generates in sections like data and bss. Sometimes, however, you need additional sections, or you need certain particular variables to appear in special sections, for example to map to special hardware. The section attribute specifies that a variable (or function) lives in a particular section. For example, this small program uses several specific section names:

              struct duart a __attribute__ ((section ("DUART_A"))) = { 0 };
              struct duart b __attribute__ ((section ("DUART_B"))) = { 0 };
              char stack[10000] __attribute__ ((section ("STACK"))) = { 0 };
              int init_data __attribute__ ((section ("INITDATA"))) = 0;
              
              main()
              {
                /* Initialize stack pointer */
                init_sp (stack + sizeof (stack));
              
                /* Initialize initialized data */
                memcpy (&init_data, &data, &edata - &data);
              
                /* Turn on the serial ports */
                init_duart (&a);
                init_duart (&b);
              }
         

    Use the section attribute with an initialized definition of a global variable, as shown in the example. GCC issues a warning and otherwise ignores the section attribute in uninitialized variable declarations.

    You may only use the section attribute with a fully initialized global definition because of the way linkers work. The linker requires each object be defined once, with the exception that uninitialized variables tentatively go in the common (or bss) section and can be multiply “defined”. You can force a variable to be initialized with the -fno-common flag or the nocommon attribute.

    Some file formats do not support arbitrary sections so the section attribute is not available on all platforms. If you need to map the entire contents of a module to a particular section, consider using the facilities of the linker instead.

 

原文见：http://mcuos.com/archiver/tid-2780.html