Skip to content

document that extern statics may be bigger than the declared size #2334

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
RalfJung wants to merge 1 commit into
base: master
Choose a base branch
from
+4 −0
Open

document that extern statics may be bigger than the declared size #2334

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
4 changes: 4 additions & 0 deletions src/items/external-blocks.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -74,6 +74,10 @@ Extern statics can be either immutable or mutable just like [statics] outside of
r[items.extern.static.read-only]
An immutable static *must* be initialized before any Rust code is executed. It is not enough for the static to be initialized before Rust code reads from it. Once Rust code runs, mutating an immutable static (from inside or outside Rust) is UB, except if the mutation happens to bytes inside of an `UnsafeCell`.

r[items.extern.static.size]
The actual memory that the extern static resolves to must have *at least* the size and alignment of the type that it was declared with in the extern block.
If the actual memory is bigger, then it is permitted to access that extra memory by creating a raw pointer to the extern static (`&raw const/mut STATIC`, no intermediate reference) and then doing appropriate pointer arithmetic.

r[items.extern.abi]
## ABI

Expand Down
Loading