implementing Struct Packing and Misaligned Access in C - advanced patterns on ARM Architecture
I'm stuck on something that should probably be simple... I've been banging my head against this for hours. I'm working on a personal project and I'm working on a project and hit a roadblock. I'm working with a question with struct packing in C when compiling for an ARM architecture. When I define a struct with various data types, I'm observing unexpected behavior due to memory alignment issues. Here's the struct I've defined: ```c typedef struct { char a; int b; short c; } MyStruct; ``` When I try to access the members of this struct, I sometimes get incorrect values, especially when `b` is accessed after a series of manipulations. I suspect this might be related to how the struct is aligned in memory. I've tried using `#pragma pack(1)` to enforce 1-byte alignment, which did change the layout of the struct, but I'm still getting unexpected results. For example, with the following code: ```c MyStruct s; s.a = 'A'; s.b = 123456; s.c = 42; printf("a: %c, b: %d, c: %d\n", s.a, s.b, s.c); ``` The output is often corrupted for `b`, especially if I change the order of assignments. I've also tried checking the size of the struct using `sizeof(MyStruct)` which is returning 8 bytes, but I don't understand why it's not behaving as expected. I'm compiling this with GCC 11.2 on an ARM Cortex-M4, and I'm aware that certain architectures have strict alignment requirements. Could it be that I'm accessing misaligned memory, or is there something else at play? Any guidance on best practices for struct alignment and packing on ARM would be greatly appreciated. My development environment is Linux. I'd really appreciate any guidance on this. This is part of a larger service I'm building. Thanks in advance! Any feedback is welcome!