ARMCC: VARIABLES GET LOCATED TO RW RATHER THAN ZI

Information in this article applies to:

• RealView MDK-ARM 3.1 and above

QUESTION

For the following example code:

char test_array[8];

The linker reports these memory sizes RW data = 8 and ZI data = 0

While for:

char test_array[9];

The linker reports these memory sizes RW data = 0 and ZI data = 9.

Why is the latter in the ZI section but the former isn't? Is there a way to change the linker behaviour?

ANSWER

Data objects smaller than 9 bytes get moved to the RW region for optimization reasons. This threshold can be controlled by the bss_threshold compiler switch. To enable this option in µVision please add the compiler switch in Options for Target — C/C++ — Misc Controls field.

Example:

--bss_threshold=0

Note:

• Changing the bss_threshold setting might result in increased code size.

SEE ALSO

• ARM Support FAQ: Placement of small global ZI data (<= 8 bytes) in memory
• Compiler Reference Guide: Command-line options

FORUM THREADS

The following Discussion Forum threads may provide information related to this topic.

• How to define variable to ZI area

Last Reviewed: Wednesday, January 25, 2017