Doubt about how a linker builds a memory image

funkymunky · 02-18-2005, 01:16 AM

Hi everyone,

I have a doubt regarding the way a memory image is build by the linker (ld, in my case) with the output files. I dont have a Comp.Sc background, so i havent studied these things formally.

Suppose i have 2 kb of code i want to load into memory (0x0 to 0x800000 ). The output has two sections of 1kb each, one of which has to be put on location 0x200000 and the other on location 0x600000. Howdoes the linker ensure that the correct data is put at the correct location? I mean, does it generate a huge image of size 0x600000 + 1kb that has data at the correct locations, and the intermediate spaces padded?? what sends the data finally to the correct location?

Plz help!

Thanx in anticipation,

Mayank
thoroughly

itsme86 · 02-18-2005, 08:04 AM

Where do you get the idea that the sections have to be loaded at different memory addresses? The only thing that I'm aware of that's consistent is the starting address of every program in virtual memory.

funkymunky · 02-18-2005, 10:46 AM

Lets forget about virtual memory for a while..im talking about microcontrollers running without an OS..im working on the Atmel At91rm9200, that has a little RAM and no Flash. I may have the code (.text) section at one memory location and a data section at another location.

itsme86 · 02-18-2005, 11:48 AM

According to ld's man page you can use:

Code:

       --section-start sectionname=org
           Locate a section in the output file  at  the  absolute
           address given by org.  You may use this option as many
           times as necessary to locate multiple sections in  the
           command  line.  org must be a single hexadecimal inte-
           ger; for compatibility with  other  linkers,  you  may
           omit  the leading 0x usually associated with hexadeci-
           mal values.  Note: there  should  be  no  white  space
           between sectionname, the equals sign (``=''), and org.

funkymunky · 02-18-2005, 11:59 AM

okay, now u and i are on the same wavelength..
My doubt was..How is the option uve mentioned above IMPLEMENTED by the linker? How does it make sure that the data will actually be at these locations once its loaded into the uC? What is there in the space between these sections??

Regards
Mayank