This should get rid of preloader warnings on old versions of macOS.
Thanks to Gijs Vermeulen for help with debugging and testing this patch.
Ideally, we would like to use vm_allocate, but since the preloader runs
very early during the startup of the process, we don't have all required
libc functions available. Also, we don't want to reimplement it ourself,
which would be very unreliable in practice.
For now, lets just use mincore() to check if there are any other pages
mapped within the area, and then fallback to MAP_FIXED.
(cherry picked from commit f254a73e6624a8603dbe310d9ee9b427145c8057)
This change should fix compatibility with old versions of macOS.
Thanks to Gijs Vermeulen for help with debugging and testing this patch.
Old versions of libsystem_c.dylib crash while running initializers when
the application does not contain a PAGEZERO section. This is probably
caused by an incorrect comparison against NULL instead of (void *)-1.
Unfortunately, when we just add a PAGEZERO section, we trigger the next
bug - no matter if we actually use the page at address (void *)0 or not,
it will not be used because the relocation code tries to find a memory
hole of size (highAddr - lowAddr) ~ 2GB.
We might be able to workaround this issue by manually reordering the
sections in the main executable, but for now lets just drop the fixed
image base. Please note that this introduces a risk of conflicts with
builtin DLLs, which will be resolved in the next patch.
(cherry picked from commit e9daff5bc8f6c7f69055b358f59ac7e662a982b4)
