ARMCC: Heap functions are not thread safe in ArmClang compiler AC6

Information in this knowledgebase article applies to:

• Keil MDK

SYMPTOM

I noticed that my heap is getting corrupted when using malloc() and free() in mutiple threads using the Arm Compiler 6. It seems like that the _mutex_* functions that should protect the heap functions are getting optimized out. This did not occur with Arm Compiler 5.

CAUSE

The _mutex_*() functions that are implemented in the CMSIS RTX library are being removed from the link by unused section elimination when using the ArmClang compiler/linker

RESOLUTION

In the "Options for Target..." - "Linker" tab, enter the following in the Misc Controls window:

--keep=_mutex_*

MORE INFORMATION

• Refer to --keep=section_id in the Linker User Guide.
• Refer to "Management of locks in multithreaded applications" section in the ARM Compiler ARM C and C++ Libraries and Floating-Point Support User Guide.
• Refer to "How to ensure re-implemented mutex functions are called" section in the ARM Compiler ARM C and C++ Libraries and Floating-Point Support User Guide.

Last Reviewed: Thursday, October 8, 2020