This code would put foo in the .rodata memory region. How does one achieve this in Rust? static const does not seem to be valid Rust, and if I understand correctly, a const in Rust is more like a #define in C.
To give some context, I'm working on a driver for a XIP flash (eXecute In Place) for a microcontroller.
The MCU has a peripheral to read data from flash on the fly, but it needs an address to a lookup table that defines the commands needed to interface the particular flash IC on your board. This lookup table must be in RAM, since the peripheral can't read it from flash before it knows how to read from flash. The peripheral can access the lookup table if it's located in the on-chip RAM though.
Put another way: I have a function that takes an address to where the lookup table is located. The address is an 32-bit unsigned integer, as this is what needs to be written to the peripheral register.
fn set_lookup_table(address: u32);
What can I pass to that function if I have this?
const FLASH_LOOKUP_TABLE: [u32; 128] = [0; 128];
EDIT: I want a single instance of the lookup table in memory. I don't want different references to FLASH_LOOKUP_TABLE to point to different places in memory.
If you pass &FLASH_LOOKUP_TABLE as u32 to the function, it will receive the address of some instantiation of FLASH_LOOKUP_TABLE as a static variable. The compiler generally tries not to duplicate it, but to entirely rule out duplication, you'd have to make it a static. If you want to control exactly where the constant data is placed by the linker, you can use the link_section attribute. What exact target triple are you using to compile your program?
If you use a static with no interior mutability, then it will be placed in a section designated for read-only non-executable data. It is very likely the same section that a static const in C would end up in. Whether the data ends up in RAM or in flash is up to the linker for that particular embedded target; it would make sense if it was placed next to the .text section, but I haven't tested it myself.
Overall, it would probably be a good idea to test a regular static first, and if that doesn't do what you want, then you can start playing with link_section tricks.