analyze: Lifetimes are incorrectly added to public extern C functions

[ahomescu]

Running the analyzer on amalgamated CFS adds lifetimes to pointer arguments of publicly exported C functions part of the public API (not called from inside CFS), e.g.

#[no_mangle]
pub unsafe extern "C" fn OS_GetLocalTime<'h0>(mut time_struct: &'h0 (OS_time_t)) -> int32 {
// 5927: mut time_struct: typeof(_1) = *mut {g68} DefId(0:6740 ~ cfs_rust_amalgamated[9f4b]::OS_time_t)
// 5927: mut time_struct:   g68 = UNIQUE | NON_NULL, (empty)
    if time_struct.is_null() { 

where the original function signature was pub unsafe extern "C" fn OS_GetLocalTime(mut time_struct: *mut OS_time_t) -> int32.

[ahomescu]

@spernsteiner Do you have time to look into this? Should I take a pass at it?

[spernsteiner]

IIRC this is basically intended/expected behavior at the moment. We've mainly been targeting application code, where callers can be updated in lockstep when function signatures change. It's generally hard to tell which things are actually "publicly exported" as part of the library API as opposed to just being non-static so they can be called from another compilation unit within the same library. (Knowing that a particular function is/isn't called elsewhere within the library doesn't necessarily help with getting a precise answer here.)

One thing we've talked about doing in the past is splitting API functions into an internal version whose signature we can change and an external shim that keeps the original signature and converts the arguments/return value to match the new signature. In this case, it might look like this:

#[no_mangle]
pub unsafe extern "C" fn OS_GetLocalTime(mut time_struct: *mut OS_time_t) -> int32 {
    OS_GetLocalTime_internal(&*time_struct)
}

unsafe fn OS_GetLocalTime_internal<'h0>(mut time_struct: &'h0 (OS_time_t)) -> int32 {
    // Actual logic goes here
}

There's some code in rewrite::shim that could potentially be reused to generate the shims. We already do this in some cases where a function that's marked non-rewritable/FIXED calls into one that we do want to rewrite.