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Compiler/TMS320F280049: what if define a variable in both CMD and main.c?

Aki Li
Genius 9365 points
Part Number: TMS320F280049

Tool/software: TI C/C++ Compiler

Customer found a defined global variable had also been already assigned in the CMD file in their firmware, but there was no compiler errors reported.  Will it be an issue? Thank you.

  • 0
    TI__Guru**** 243830 points

    For now, I presume you use COFF ABI, and not the recently introduced EABI. 

    This symbol written in C ...

    /* C file */
int global_variable;

    ... and this symbol written in the linker command file ...

    /* linker command file */
global_variable = 0xa000;

    ... are different symbols.  Search for those symbols in the linker map file.  Both symbols are present, with different values.  The symbol from the C file is written _global_variable in the automatically generated assembly file.  An underscore character is added to the beginning.

    Aki Li said:
    Will it be an issue?

    If the user intends for these symbols to be different, then no.  

    If you change to EABI, it won't work.  In EABI, a symbol is written the same way everywhere.  The underscore character is not added to the beginning.  In that case, those symbols are the same, and you see an error when you build.

    Thanks and regards,

    -George

  • 0 in reply to George Mock
    TI__Genius 9365 points

    George,

    Thank you. Customer said they already add an underscore character before the variable in the CMD, i.e, _global_variable.  And they found it could not work, unless they disabled the variable in C file.

  • 0 in reply to Aki Li
    TI__Guru**** 243830 points

    Aki Li said:
    they found it could not work

    Please give a detailed description of what happens when it does not work.  What does the customer see?  What does the customer expect instead?

    Please search the C28x assembly tools manual for the sub-chapter titled Using Linker Symbols in C/C++ Applications.  Perhaps that documentation will solve the problem.

    Thanks and regards,

    -George

  • 0 in reply to George Mock
    Prodigy 210 points

    Hi, George

         if we define the variable in  the linker command file  as  _global_variable, how do the compiler deal with the conflict? there are the one address of the global_variable or the two address of the global_variable?

    thank you. 

  • 0 in reply to Mark-Lu
    TI__Guru**** 243830 points

    Mark-Lu said:
         if we define the variable in  the linker command file  as  _global_variable, how do the compiler deal with the conflict?

    If you define it in C code as ...

    extern int global_variable;

    ... then there is no conflict.  They are are viewed as the same symbol.

    If you define it in C code as ...

    int global_variable;  /* no extern */

    Then you get an error diagnostic when you link.  The linker complains about multiple definitions of the same symbol.

    Thanks and regards,

    -George