document that extern statics may be bigger than the declared size - #2334
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RalfJung wants to merge 1 commit into
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document that extern statics may be bigger than the declared size#2334RalfJung wants to merge 1 commit into
RalfJung wants to merge 1 commit into
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| 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 and then doing appropriate pointer arithmetic. |
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Perhaps be more explicit about the need to use &raw (and avoid an intermediate reference)?
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I am fairly sure we discussed at some point whether it's okay to access memory beyond the declared size of an
extern static, and @nikic confirmed that this is fine. But I couldn't find any official place where we document this. So, let's add it to the Reference.I wondered if we also need the converse on the UB page: it is UB to even start the program if an extern static ends up being backed by memory that is smaller or less-aligned than the declared type. What do you think?
Cc @rust-lang/opsem