GCC 变量映射和MISRA-C

Question

I know mostly two ways (with many variants, use bifields, data structures per peripheral, etc...) to declare memory mapped registers with GCC:

• either use a pointer initaliased to the right adress like volatile uint32_t *pMyRegister = (uint32_t *)0xDEADBEEFUL;
• or define a variable and map it manually like volatile uint32_t MyRegister __attribute((section(".register_section"))); and then map the section in the LD file.

Unfortunately none of these ways seem compatible with MISRA-C coding rules, the first one because there is an unauthorized (by MISRA) cast from integer to pointer, the second because of the attribute keyword.

My question is: is there a way (with the second solution) to map a variable in a section without affecting the ANSIness of the code (ie. no compiler specific keyword).

Thank you

Answer 1

First of all, neither is correct because of missing volatile . See How to access a hardware register from firmware? which also briefly addresses MISRA-C.

To answer the question, this rule MISRA-C:2012 11.4 is advisory and comes with a rationale that says (the note in the end was appended by me):

"...but may be necessary when addressing memory mapped registers or other hardware specific features. If casting between integers and pointers is used, care should be taken..." [to not cause misalignment undefined behavior]

So you can safely ignore this rule for your register declarations and if needed refer to the rationale of rule 11.4. Since it is advisory, no deviation is required (but preferably you should document that you ignore the rule still).

Notably the former of your two versions is preferable from a MISRA-C perspective, since it doesn't contain non-standard extensions that you need to document how they are used, which is otherwise required as per other MISRA rules.