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const section is not being created for CONST ARRAY Dat Items by the compiler

Pashan
Intellectual 715 points

Hello Support,

For CONST data item I see that the compiler generates .const section.

But when the CONST data item is a MATRIX, then I see that the section name is changed to something like .const:XXXXXX.

Any clue aboutthe rule for section name creation by the compiler when the user doesn't use any PRAGMA.

Also, how does the linker allocate those .const:XXXX section names within the .const section, even though the exact section name is missing in the Linker Command File?

I am using TMS470 4.6.4 compiler.

It is a C code which I am compiling.

Some snippet from MAP file will indicate the question I am asking:

.Layer2_Const
*          0    00008050    00000978    
                  00008050    000002f8     hzspicnf.obj (.const:SPI_Messages_Database)  --- Why the section name is not .const
                  00008348    00000008     hzspicnf.obj (.const)
                  00008350    00000058     hcnvm.obj (.const:nvm_stage_process)
                  000083a8    00000010     hcnvm.obj (.const)
                  000083b8    00000020     hi

Thank you.

Regards

Pashan

 

  • 0
    TI__Guru**** 244300 points

    This wiki article talks about something similar.  I don't recommend you adopt the techniques contained in that article.  But the method it uses to remove unused variables is the same as the one the compiler employs to remove C const variables that end up not getting used.  Pay particular attention to this piece of the article.

    Thanks and regards,

    -George

  • 0 in reply to George Mock
    Intellectual 715 points

    Hello George,

    Thank you for the pointer.

    But this didn't answer my exact question.

    The article tells me how to create SECTION Names so that the linker removes it.

    I am asking different.

    I am writing a C program in the usual way and not creating any new section names as mentioned in the WIKI.

    Hence, when I open the LISTING File, I should see all my CONST variables under .const section.

    But for some multi-dimensional arrays, I see then under section name .const:XXXXX.

    Question is why not those multi-dimensional arrays are within .const section and instead under .const:XXXXX section?

    Please help me to understand the algorithm followed by the C Compiler to generate those enhanced .const:XXXXX section names only for certain symbols.

    Thank you.

    Regards

    Pashan

  • 0 in reply to Pashan
    TI__Guru**** 244300 points

    Well, let's define some terms first.  An input section is a section created by the compiler (assembler, really), and comes from a single source file.  The linker creates an output section by combining together one or more input sections.  The confusing part is that an input section often has the same name as the output section which contains it.  Even so, it is best to view them as different sections.  A scalar is a simple variable such as "int i;", while an aggregate is an array, struct, or union.  

    With that terminology in mind, your question is: When does the compiler place a variable in an input section merely named .const, and when does it place it in an input section with a name of the form .const:name_of_variable?  Scalars and very small aggregates are placed in an input section named .const.  Aggregates larger than some small size are placed in input sections named .const:name_of_variable.

    Thanks and regards,

    -George

  • 0 in reply to George Mock
    Intellectual 715 points

    George,

    Thank you for the exact response I was looking for.

    Now, the next question is what is the THRESHOLD of the size of data item beyond which triggers the renaming from default .const to .const:variable_name section by the compiler?

    This will help me a lot.

    Thank you.

    Regards

    Pashan

     

  • 0 in reply to Pashan
    TI__Guru**** 244300 points

    Any data object larger than 32 bytes is placed in a sub-section of the form .const:name_of_variable.

    Thanks and regards,

    -George