When ld64 links a binary deterministically using the flag ZERO_AR_DATE, it sets
a timestamp of 0 for N_OSO members in the symtab section, rather than the usual
last modified date of the object file. Prior to this patch, lldb would compare
the timestamp from the N_OSO member against the last modified date of the object
file, and skip loading the object file if there was a mismatch. This patch
updates the logic to ignore the timestamp check if the N_OSO member has
The original logic was added in https://reviews.llvm.org/rL181631 as a safety
check to avoid problems when debugging if the object file was out of date. This
was prior to the introduction of deterministic build in ld64. lld still doesn't
support deterministic build.
Other code in llvm already relies on and uses the assumption that a timestamp of
0 means deterministic build. For example, commit
9ccfddc39d4d27f9b16fcc72ab30d483151d6d08 adds similar timestamp checking logic
to dsymutil, but special cases timestamp 0. Likewise, commit
0d1bb79a0413f221432a7b1d0d2d10c84c4bbb99 adds a long comment describing
deterministic archive, which mostly uses timestamp 0 for determinism.