嵌入式系统内存冲突

Question

I am building an application with Diab compiler for PowerPC. I am having an issue with memory conflict.

In header1.h I have declared

...
void NullFunct_1 (int);
...

The function NullFunct_1 is then defined in main.c

    #include "header1.h"
...
           void NullFunct_1 (int f)
           {
              return;
           }

In header2.h I have declared

    struct tp_key 
    {
        int a;                    
        void (*fn_ptr)(int);     // function pointer    
        unsigned int b;             
        unsigned int c;                
        int d;                  
        int e;                 
    };

In header2.c I initialize the array Key as follow

struct tp_key Key[48] = {0, &NullFunct_1, 0, 0, 0, 0};

In header3.h I declare the global variable Units

extern int Units;

In header3.c I define and initialize the variable Units

int Units = 0; //Units variable can then assume the values of 0, 1000 or 10000 only.

The program is compiled and linked without errors generating the executable.

The Link Editor Memory Map generated is the following

    input           virtual                        
    section         address     size     file
...
    .data           50036adc    00000484 header2.o
           Key      50036adc    00000480
           Xxxx     50036f5c    00000004

    .data           50036f60    00000170 header3.o
           Units    50036f60    00000004
...
...
        NullFunct_1 500038b8    0000000c main.o
...

You may notice the variables Key and Units are memory "neighbors" 0x50036adc + 0x480 = 0x50036f5c .

In some cases the variable Units contains value 1342191800 (0x500038B8 in hex) that corresponds to the memory address of the variable Null_Funct_1

This happens because of the instruction

struct tp_key Key[48] = {0, &NullFunct_1, 0, 0, 0, 0};

Is this a linker problem that did not calculate the memory size of the variable Key correctly? or did I make a mistake? Even if there is a linker problem then may you suggest how to avoid such kind of problems, please?

Answer 1

There are no "conflicts" here.

sizeof(struct tp_key) [24] * 48 in hex is 0x480. So everything is 100% fine.

My advice: do not focus on chasing "compiler errors". Assume that the compilers were tested and are used by millions of programmers.

Answer 2

Key has 48 elements but in my source code I assigned variable Key[48] and it is, of course, incorrect. The cause of the error in the code is

for ( i=0; i <= 48; i++) 
{ 
     Key[i].fn_ptr = &NullFunct_1; 
}

To fix the problem I changed the for loop as follow

for ( i=0; i < 48; i++) 
{ 
     Key[i].fn_ptr = &NullFunct_1; 
}