It can pick whatever value it wants and doesn't have to care what the program is doing.
Also the value has to stay the same until it's 'replaced'.
> Are we talking about all zeros?
It might be, but probably won't be. What makes you bring up all zeroes?
> Is the implementation not permitted to use whatever arbitrary value was in memory? Why not?
(Edit: probably wrong, also affects other things I said) It can. What suggests it wouldn't be able to?
> 2. What’s up with [[indeterminate]]? I would expect “indeterminate” to mean that the variable has a value that happens to be arbitrary (and may contain sensitive data, etc), not that it turns back into actual UB.
"has a value that happens to be arbitary" would be the default without [[indeterminate]]. Well, it can also error out if the compiler wants to do that.
If that's what they're going for, it's way too much weight to hang on a single vague word like that. Trying to define "state of the program" in a detailed way sounds nightmarish. Let's say I'm the implementation. If I go get fresh (but not zeroed) memory from the OS to put my stack on, the garbage in there isn't state of the program, right? If I then run a function and the function exits, is the garbage now state of the program, or is it outside the state of the program? If I want a fixed init value per address, is that allowed as a hardening feature or disallowed as being based on allocation patterns? Does the as-if rule apply, so I'm fine if the program can't know for sure where I got my arbitrary byte values from?
And would that mean there's still no way to say "Don't waste time initializing it, but don't do any UB shenanigans either. (Basically, pretend it was initialized by a random number generator.)"
> Let's say I'm the implementation. If I go get fresh (but not zeroed) memory from the OS to put my stack on, the garbage in there isn't state of the program, right?
I'd argue that once you get the memory it's now part of the state of your program, which precludes it from being involved in whatever value you end up reading from the variable(s) corresponding to that memory.
> If I want a fixed init value per address, is that allowed as a hardening feature or disallowed as being based on allocation patterns?
I'd guess that that specific implementation would be disallowed, but as I'm an internet nobody I'd take that with an appropriately-sized grain of salt.
> And would that mean there's still no way to say "Don't waste time initializing it, but don't do any UB shenanigans either. (Basically, pretend it was initialized by a random number generator.)"
I feel like you'd need something like LLVM's `freeze` intrinsic for that kind of functionality.
It can pick whatever value it wants and doesn't have to care what the program is doing.
Also the value has to stay the same until it's 'replaced'.
> Are we talking about all zeros?
It might be, but probably won't be. What makes you bring up all zeroes?
> Is the implementation not permitted to use whatever arbitrary value was in memory? Why not?
(Edit: probably wrong, also affects other things I said) It can. What suggests it wouldn't be able to?
> 2. What’s up with [[indeterminate]]? I would expect “indeterminate” to mean that the variable has a value that happens to be arbitrary (and may contain sensitive data, etc), not that it turns back into actual UB.
"has a value that happens to be arbitary" would be the default without [[indeterminate]]. Well, it can also error out if the compiler wants to do that.