[Bug ld/22589] aarch64: adrp relocation gets filled with non-zero address for undefined weak symbol

[rearnsha at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=22589

Richard Earnshaw <rearnsha at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |rearnsha at gcc dot gnu.org

--- Comment #3 from Richard Earnshaw <rearnsha at gcc dot gnu.org> ---
It's simply not safe to use adrp to reference a weak symbol.  If you're
hand-writing assembly you have to be aware of this.

adrp is a position-independent address-forming instruction; as such it cannot
ever resolve to zero and still be position independent; that would require
dynamic relocation which would in turn imply having a writable text section. 
Furthermore, the offset range of adrp is such that it probably could not
generate zero.

It might be nice if the assembler/linker could detect this case and emit an
out-of-bounds error - it's essentially a relocation overflow.  I'm not sure if
that's a generic issue or a back-end one.

Anyway, it's still invalid to use adrp to form a reference to a weak symbol.

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