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How to use RELATIONAL Expressions in Linker Command File

Pashan
Intellectual 715 points

Hello,

In the spnu118h.pdf within the following section:

7.13.3 Assignment Expressions

there is a Table of Expressions with the following title: 

Table 7-2. Groups of Operators Used in Expressions (Precedence)

Please help me understand how do I use the RELATIONAL Expressions using Linker Symbols within a Linker Command File as mentioned in the above mentioned document.

The document title is:

ARM Assembly Language Tools

v4.6

User's Guide

Literature Number: SPNU118H

September

Thank you.

Regards

Pashan

  • 0
    TI__Guru**** 253380 points

    This is a rather general question, so it is difficult to answer.  What is the overarching problem you want to solve?  

    The only expressions you can write in a linker command file are assignments.  There is no control flow (i.e. if statements).  So you can only write something like

    global_sym1 = global_sym2 >= global_sym3;

    global_sym1 is assigned the value 1 or 0 based on that relational expression.  Experiment with toy examples to get a feel for how it works.  

    Hope this helps ...

    -George

     

  • 0 in reply to George Mock
    Prodigy 230 points

    Imagine that you need define the maximum load address (that will go to the image) at link time (e.g. I needed this for special CRC-like header for the image).

    You can get load address, run address and size of the sections, also you can use "dot"-operator to get like-current address.

    But, further imagination, your sections have a big variety of load and start addresses, you can't GROUP them and "dot"-operator is also useless. You can get only load address, run address and size for each section. So how to get the maximum address?

    Lets we have __section_1_start, __section_1_size, __section_2_start, __section_2_size, __section_3_start and __section_3_size.

    define __section_x_end = __section_x_start + __section_x_size; for each.

    Now,

    __max_addr = __section_1_end;

    __compare = __max_addr > __section_2_end;

    __max_addr = __max_addr * __compare + __section_2_end * !__compare;

    __compare = __max_addr > __section_3_end;

    __max_addr = __max_addr * __compare + __section_3_end * !__compare;

    So now __max_addr hold our goal...

    But also we get warnings about symbol redifinition and symbol from different sections combining...

    Oh, maybe I missed some conditional operator in the linker symbols expressions??? :)