Make start address of osReserveHeapMemory tunable via command line -xb
We stumbled upon a case where an external library (OpenCL) does not work
if a specific address (0x200000000) is taken.
It so happens that osReserveHeapMemory starts trying to mmap at 0x200000000:
void *hint = (void*)((W_)8 * (1 << 30) + attempt * BLOCK_SIZE); at = osTryReserveHeapMemory(*len, hint);
This makes it impossible to use Haskell programs compiled with GHC 8
with C functions that use OpenCL.
See this example https://github.com/chpatrick/oclwtf for a repro.
This patch allows the user to work around this kind of behavior outside
our control by letting the user override the starting address through an
RTS command line flag.
Reviewers: bgamari, Phyx, simonmar, erikd, austin
Reviewed By: Phyx, simonmar
Subscribers: rwbarton, thomie
Differential Revision: https://phabricator.haskell.org/D2513
(cherry picked from commit 1b5f9207a649a64a1bba20b0283253425f9208d7)