Fix calling pvPortMalloc on FreeRTOS with size zero resulting in vApplicationMallocFailedHook getting called and FreeRTOS asserting

[Thom747]

Pull request

Choose Correct

• bug
• feature

According to the C standard, section 7.22.3, clause 1 calling malloc() with size zero is implementation-defined.
The following is a direct quote from the standard:

If the size of the space requested is zero, the behavior is implementation-defined: either a null pointer is returned, or the behavior is as if the size were some nonzero value, except that the returned pointer shall not be used to access an object.

Unfortunately, FreeRTOS is not compliant with this definition.
If vApplicationMallocFailedHook() is defined, it will be triggered, leading to user-defined error handling.
After this, in some heap implementations (notably heap_4.c) an assert is hit as the pointer intended to be returned is NULL.
For most implementations of the assert, this will either result in a crash or an infinite loop.

As this behaviour is incompatible with what eRPC expects to happen (a nullptr being returned), this PR adds a guard against calling pvPortMalloc() with a zero size argument.

To Reproduce

Send an empty (zero-size) list to a FreeRTOS-based system using erpc_c.

Expected behavior

FreeRTOS does not assert and vApplicationMallocFailedHook() is not triggered.
A nullptr is returned to the caller.

Desktop (please complete the following information):

• OS:
  • Irrelevant.
• eRPC Version:
  • 1.14.0.

Steps you didn't forgot to do

• I checked if other PR isn't solving this issue.
• I read Contribution details and did appropriate actions.
• PR code is tested.
• PR code is formatted.
• Allow edits from maintainers pull request option is set (recommended).