dyld has two notification functions - a native one, and one that
it rewrites its arguments for, for lldb. We currently use the
latter, _dyld_debugger_notification. The native notification
function, lldb_image_notifier (and on older systems, gdb_image_notifier)
we can find by name, or if libdyld shows no dyld loaded in the
process currently, we can get it from the dyld_all_image_infos
object in memory which we can find with a system call. When we do
a "waitfor attach" to a process on a modern darwin system, there
is a transition early in launch from the launch dyld to the
shared-cache-dyld, and when we attach in the middle of that transition,
libdyld will say there is no dyld present. But we can still find
the in-memory dyld_all_image_infos which has the address of the
shared cache notifier function that will be registered in the
process soon.
This change will result in a much more reliable waitfor-attach.
This is the third landing of this patch. We have an Intel mac
CI bot that is running an older (c. 2019) macOS 10.15, I had to
reproduce that environment and found the name of the notifier
function had changed which was the cause of those failures.
Differential Revision: https://reviews.llvm.org/D139453
rdar://101194149
ec360faeb3