Debug to Release causes different application behavior

Hi,

I'm trying to understand how memory is allocated in the Release configuration vs. Debug and how to debug memory corruption issues that only appear in Release.

I'm coding for the STM32F4 using CrossStudio 2.3.3

I've reviewed Paul Curtis' helpful hints at the following links:

• https://rowley.zendesk.com/entries/46174-Changing-build-configuration-from-Debug-to-Release-causes-different-application-behaviour
• https://rowley.zendesk.com/forums/51134/entries/46195

I have copious amount of memory allocated to stack: 2048 to Main; 1024 to Heap, and 512 to Process (in both Release and Debug)

If I make the stupid mistake of assigning a larger argument for string size to function snprintf than is allocated to the string, I run into memory corruption and undefined behavior. That much I would expect. But, I would like to know why the behavior only surfaces in Release and not in Debug.

An example would be the following:

<code>

static uint8_t Percent_Text[6] = {' '}

void Update_WastePercentage(uint32_t Percent, uint8_t UpdatePercentage)
{
if (RollOver == NO) {
if (Percent == 0) {
strncpy(Percent_Text, " 0", 10);
}
else if (Percent == 1000) {
strncpy(Percent_Text, " 100", 10);
}
else {
snprintf(Percent_Text, 10, "%2d.%d", Percent/10, Percent%10);
}

}
else {
strncpy(Percent_Text, " ?", 10);
}

LCD_DisplayChangedString(216, 95, 4, Percent_Text, Percent_Text_Prev, UpdatePercentage);
}

</code>

Now, this code executes as expected in Debug. In Release, however, the string in "Percent_Text", although correct numerically, is output in a different color on the LCD, but only where the strncpy function was used. That is to say, if the percent is "0" or "100" or has "?", it is not output to the LCD in the predestinated color (white), but in black. I'm using global variables g_InfoTextColor and g_InfoBackColor. In this situation, I assume memory allocated to the LCD color variable is being overwritten by this function, because although I have told strncpy to verify that no more than 10 characters be included in the string, the compiler has only allocated 6. And, the LCD color variable resides right next to it in memory is my guess (or has not been defined at this point).

Additionally, one will note that I don't need to use strncpy for the above examples, as the string length is clearly defined. However, this behavior does not always surface, I assume, because memory is allocated in different locations and not all are initialized the same way.

Now, if I change the size argument in the strncpy function to 6 in the above example or change strncpy to strcpy, the problem goes away. Again, why does this behavior only surface in Release and not in Debug.

What is the strncpy function and Release property doing that creates this behavior? Additionally, I can't debug this. How can it be debugged when it only appears in Release and all the Release options are changed to match Debug (or vise versa)?

kind regards,

MAJ

EDIT: Is there a code or block tag we can use?