https://sourceware.org/bugzilla/show_bug.cgi?id=22589
Szabolcs Nagy <nsz at gcc dot gnu.org> changed:
What |Removed |Added
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CC| |nsz at gcc dot gnu.org
--- Comment #9 from Szabolcs Nagy <nsz at gcc dot gnu.org> ---
i ran into this again and i think the linker could relax 'adrp xN, weaksym'
into 'mov xN, 0' if weaksym is undefined.
link error is not helpful since such code (accessing weak symbols) may be
behind checks and unreachable if the symbol is undefined.
normally weak syms are accessed via GOT which can be 0 for undef, but in PIC
this depends on a dynamic relocation even for hidden visibility syms. this does
not work in early start code (e.g. *crt1.o) accessing weak, linker generated
symbols (such as __ehdr_start) where the code must not generate dynamic
relocations (since it may be executed before ld.so or static pie self
relocation). if such symbol is potentially undefined then we have a problem:
adrp does not work, GOT does not work, movz does not work. so i dont see a way
to implement
if (&weaksym != 0)
use(&weaksym);
logic in the ld.so or static pie start code. i ran into this with the morello
port where there are linker created symbols (__rela_dyn_start) that are only
defined under certain conditions (static exe with no dynamic-linker) and must
be checked and accessed in gcrt1.o that is used in both pde and pie.
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