We changed to `llvm.compiler.used` because of the behaviour of `gold`,
which refuses to coalesce sections that have different `SHF_GNU_RETAIN`
flags, which causes problems with metadata.
Originally I thought we were going to have to generate two sections
with distinct names and have the runtime look for both of them, but
it turns out that the runtime only wants to see sections that have
`SHF_GNU_RETAIN` in any case. It's really the reflection code that
is interested in being able to see non-retained sections. The upshot
is that we don't need to use `llvm.compiler.used`; it's just fine if
we have duplicate sections, as long as the reflection code looks for
them when it's inspecting an ELF image.
This also means we no longer need to pass `-z nostart-stop-gc` to the
linker if we're using `lld`.
rdar://123504095
ELF's lack of linker directives is worked around by a custom section
(`.swift1_autolink_entries`). This is metadata that is not intended to
be emitted into the linked binary. A previous change introduced the use
of a module (global) assembly gadget to discard the section. However,
this interacts poorly with ASAN which would instrument the section,
resulting in a strong reference. This reference would persist to a
discarded symbol. lld would object to this. Blacklist the symbol to
ensure that ASAN + autolinking can co-exist.
Mark the section .swift1_autolink_entries as SHF_EXCLUDE
so the section will get dropped by the linker after linking the final
binary.
This section is used to save the flags needed for auto link and there
is no reason it should stay in the final linked binary.Mark the
section .swift1_autolink_entries as SHF_EXCLUDE
so the section will get dropped by the linker after linking the final
binary.
This section is used to save the flags needed for auto link and there
is no reason it should stay in the final linked binary.
This solves issue SR-11247
