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Problem with Compiler/linker Generating code for indirect function pointers

Shrinath Eswarahally

void sys_startup_init(BOOL8 shutdown)
{
//
// Check for operating mode
//
if (!shutdown)
{
// setup MMU
shutdown = (*isys_startup_mmu_init)(shutdown);



....
}

// Shutdown if mode is not normal
....
}

The sys_startup_init function is entered from assembly code.

The code shutdown = (*isys_startup_mmu_init)(shutdown);
function pointer is where the code execution is incorrect.


Changing the function to :
void sys_startup_mmu_init(void)

results in the correct code being executed. However is not possible to change all the indirect function calls in this manner, so this is not a feasible solution.

C compiler version: 7.07h

Parents
  • 0 in reply to Andy Neil

    That would be true if the orinional programmer, on my project did not decide that he wanted floats and function pointers, then it would not fit so lets add bank switching. My program pass to many parameters, so I need reentrant. My point was it is an 8051.

    Do not use C features that the 8051 does not like unless there is a real need. I my case fixed point math and flags to choose functions would have made a smaller, faster, cleaner program.

Reply
  • 0 in reply to Andy Neil

    That would be true if the orinional programmer, on my project did not decide that he wanted floats and function pointers, then it would not fit so lets add bank switching. My program pass to many parameters, so I need reentrant. My point was it is an 8051.

    Do not use C features that the 8051 does not like unless there is a real need. I my case fixed point math and flags to choose functions would have made a smaller, faster, cleaner program.

Children
  • 0 in reply to Neil Kurzman

    "My program pass to many parameters, so I need reentrant"

    That shouldn't matter.

    C51 has no specific difficulty with long parameter lists - it passes excess parameters using fixed memory locations. There is no problem provided the Linker can either work out the call tree itself, or you provide the information manually

  • 0 in reply to Andy Neil

    I did not say it would not work, it does. by 2 floats and an int requires reentrant (far as I know). The origional programmer did not ask do I need to do this. You can not write for the 51' like "memory is cheap". reentrant do not get overlaid. In my case I have several things done it the program that make it bigger and slower. And none where required. It was done like it was a PC. I just wanted to point out the poster that he may want be sure he needs to use function pointers

  • 0 in reply to Neil Kurzman

    "2 floats and an int requires reentrant"

    No, it doesn't.
    The following (admittedly trivial) function compiles OK without any need for reentrant:

    void func( float f1, float f2, float f3, float f4, int i)
{
   volatile int local_int;
   volatile int local_float;

   local_float = f1;
   local_float = f2;
   local_float = f3;
   local_float = f4;

   local_int   = i;
}
    "...none were required. It was done like it was a PC."

    Yes, that's exactly how I found out all this stuff!
    Initially, someone else started the port and used reentrant to get around the function-pointer problem - but it is not necessary. By supplying the appropriate Linker options, the Linker is able to correctly overlay these functions.

    You can (probably) reduce the overhead in your code by abandonging reentrant and using the appropriate Linker controls?

  • 0 in reply to Andy Neil

    Thanks I will keep it in mind. But, in my case 8 of 10 the function calls were set at the begining and do not change. I assume they were for future flexibility that was never needed.