1# MISRA Compliance 2 3FreeRTOS-Kernel conforms to [MISRA C:2012](https://www.misra.org.uk/misra-c) 4guidelines, with the deviations listed below. Compliance is checked with 5Coverity static analysis. Since the FreeRTOS kernel is designed for 6small-embedded devices, it needs to have a very small memory footprint and 7has to be efficient. To achieve that and to increase the performance, it 8deviates from some MISRA rules. The specific deviations, suppressed inline, 9are listed below. 10 11Additionally, [MISRA configuration file](examples/coverity/coverity_misra.config) 12contains project wide deviations. 13 14### Suppressed with Coverity Comments 15To find the violation references in the source files run grep on the source code 16with ( Assuming rule 8.4 violation; with justification in point 1 ): 17``` 18grep 'MISRA Ref 8.4.1' . -rI 19``` 20 21#### Rule 8.4 22 23MISRA C:2012 Rule 8.4: A compatible declaration shall be visible when an 24object or function with external linkage is defined. 25 26_Ref 8.4.1_ 27 - pxCurrentTCB(s) is defined with external linkage but it is only referenced 28 from the assembly code in the port files. Therefore, adding a declaration in 29 header file is not useful as the assembly code will still need to declare it 30 separately. 31 32_Ref 8.4.2_ 33 - xQueueRegistry is defined with external linkage because it is accessed by the 34 kernel unit tests. It is not meant to be directly accessed by the application 35 and therefore, not declared in a header file. 36 37#### Rule 8.6 38 39MISRA C:2012 Rule 8.6: An identifier with external linkage shall have exactly 40one external definition. 41 42_Ref 8.6.1_ 43 - This rule prohibits an identifier with external linkage to have multiple 44 definitions or no definition. FreeRTOS hook functions are implemented in 45 the application and therefore, have no definition in the Kernel code. 46 47#### Rule 11.1 48MISRA C:2012 Rule 11.1: Conversions shall not be performed between a pointer to 49function and any other type. 50 51_Ref 11.1.1_ 52 - The pointer to function is casted into void to avoid unused parameter 53 compiler warning when Stream Buffer's Tx and Rx Completed callback feature is 54 not used. 55 56#### Rule 11.3 57 58MISRA C:2012 Rule 11.3: A cast shall not be performed between a pointer to 59object type and a pointer to a different object type. 60 61_Ref 11.3.1_ 62 - This rule prohibits casting a pointer to object into a pointer to a 63 different object because it may result in an incorrectly aligned pointer, 64 leading to undefined behavior. Even if the casting produces a correctly 65 aligned pointer, the behavior may be still undefined if the pointer is 66 used to access an object. FreeRTOS deliberately creates external aliases 67 for all the kernel object types (StaticEventGroup_t, StaticQueue_t, 68 StaticStreamBuffer_t, StaticTimer_t and StaticTask_t) for data hiding 69 purposes. The internal object types and the corresponding external 70 aliases are guaranteed to have the same size and alignment which is 71 checked using configASSERT. 72 73 74#### Rule 11.5 75 76MISRA C:2012 Rule 11.5: A conversion should not be performed from pointer to 77void into pointer to object. 78This rule prohibits conversion of a pointer to void into a pointer to 79object because it may result in an incorrectly aligned pointer leading 80to undefined behavior. 81 82_Ref 11.5.1_ 83 - The memory blocks returned by pvPortMalloc() are guaranteed to meet the 84 architecture alignment requirements specified by portBYTE_ALIGNMENT. 85 The casting of the pointer to void returned by pvPortMalloc() is, 86 therefore, safe because it is guaranteed to be aligned. 87 88_Ref 11.5.2_ 89 - The conversion from a pointer to void into a pointer to EventGroup_t is 90 safe because it is a pointer to EventGroup_t, which is returned to the 91 application at the time of event group creation for data hiding 92 purposes. 93 94_Ref 11.5.3_ 95 - The conversion from a pointer to void in list macros for list item owner 96 is safe because the type of the pointer stored and retrieved is the 97 same. 98 99_Ref 11.5.4_ 100 - The conversion from a pointer to void into a pointer to EventGroup_t is 101 safe because it is a pointer to EventGroup_t, which is passed as a 102 parameter to the xTimerPendFunctionCallFromISR API when the callback is 103 pended. 104 105_Ref 11.5.5_ 106 - The conversion from a pointer to void into a pointer to uint8_t is safe 107 because data storage buffers are implemented as uint8_t arrays for the 108 ease of sizing, alignment and access. 109 110#### Rule 21.6 111 112MISRA C-2012 Rule 21.6: The Standard Library input/output functions shall not 113be used. 114 115_Ref 21.6.1_ 116 - The Standard Library function snprintf is used in vTaskListTasks and 117 vTaskGetRunTimeStatistics APIs, both of which are utility functions only and 118 are not considered part of core kernel implementation. 119
