Add a RTS option -xp to load PIC object anywhere in address space

Add a RTS option -xp to load PIC object anywhere in address space. We do
this by relaxing the requirement of <0x80000000 result of
`mmapForLinker` and implying USE_CONTIGUOUS_MMAP.

We also need to change calls to `ocInit` and `ocGetNames` to avoid
dangling pointers when the address of `oc->image` is changed by
`ocAllocateSymbolExtra`.

Test Plan:
```
$ uname -a
Linux localhost 4.18.8-arch1-1-ARCH #1 SMP PREEMPT Sat Sep 15 20:34:48
UTC 2018 x86_64 GNU/Linux
$ cat mk/build.mk
DYNAMIC_GHC_PROGRAMS = NO
DYNAMIC_BY_DEFAULT = NO

GhcRTSWays += thr_debug
EXTRA_HC_OPTS += -debug
WAY_p_HC_OPTS += -fPIC -fexternal-dynamic-refs
$ inplace/bin/ghc-stage2 --interactive -prof +RTS -xp
GHCi, version 8.7.20180928: http://www.haskell.org/ghc/  :? for help
ghc-stage2: R_X86_64_32 relocation out of range:
ghczmprim_GHCziTypes_ZMZN_closure = 7f690bffab59
Recompile
/data/users/watashi/ghc/libraries/ghc-prim/dist-install/build/HSghc-prim
-0.5.3.o with -fPIC -fexternal-dynamic-refs.
ghc-stage2: unable to load package `ghc-prim-0.5.3'
$ strace -f -e open,mmap inplace/bin/ghc-stage2 --interactive -prof
-fexternal-interpreter  -opti+RTS -opti-xp
...
[pid 1355283]
open("/data/users/watashi/ghc/libraries/base/dist-install/build/libHSbas
e-4.12.0.0_p.a", O_RDONLY) = 14
[pid 1355283] mmap(NULL, 8192, PROT_READ|PROT_WRITE|PROT_EXEC,
MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f6a84842000
[pid 1355283]
open("/data/users/watashi/ghc/libraries/base/dist-install/build/libHSbas
e-4.12.0.0_p.a", O_RDONLY) = 14
[pid 1355283] mmap(NULL, 8192, PROT_READ|PROT_WRITE|PROT_EXEC,
MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f6a84676000
...
Prelude> System.Posix.Process.getProcessID
...
[pid 1355283]
open("/data/users/watashi/ghc/libraries/unix/dist-install/build/libHSuni
x-2.7.2.2_p.a", O_RDONLY) = 14
[pid 1355283] mmap(NULL, 45056, PROT_READ|PROT_WRITE|PROT_EXEC,
MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f6a67d60000
[pid 1355283]
open("/data/users/watashi/ghc/libraries/unix/dist-install/build/libHSuni
x-2.7.2.2_p.a", O_RDONLY) = 14
[pid 1355283] mmap(NULL, 57344, PROT_READ|PROT_WRITE|PROT_EXEC,
MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f6a67d52000
...
```

```
$ uname -a
Darwin watashis-iMac.local 18.0.0 Darwin Kernel Version 18.0.0: Wed Aug
22 20:13:40 PDT 2018; root:xnu-4903.201.2~1/RELEASE_X86_64 x86_64
$ mv
/Users/watashi/gao/ghc/libraries/integer-gmp/dist-install/build/HSintege
r-gmp-1.0.2.0.o{,._DISABLE_GHC_ISSUE_15105}
$ inplace/bin/ghc-stage2 --interactive  +RTS -xp
GHCi, version 8.7.20181003: http://www.haskell.org/ghc/  :? for help
Prelude> System.Posix.Process.getProcessID
42791
Prelude> Data.Set.fromList [1 .. 10]
fromList [1,2,3,4,5,6,7,8,9,10]
Prelude>
Leaving GHCi.
$ inplace/bin/ghc-stage2 --interactive -prof -fexternal-interpreter
GHCi, version 8.7.20181003: http://www.haskell.org/ghc/  :? for help
Prelude> System.Posix.Process.getProcessID
42806
Prelude> Data.Set.fromList [1 .. 10]
fromList [1,2,3,4,5,6,7,8,9,10]
Prelude>
Leaving GHCi.
```

Also test with something that used to hit the 2Gb limit and it loads
and runs without problem.

Reviewers: simonmar, bgamari, angerman, Phyx, hvr, erikd

Reviewed By: simonmar

Subscribers: rwbarton, carter

Differential Revision: https://phabricator.haskell.org/D5195

1 files changed, 12 insertions, 0 deletions

diff --git a/includes/rts/Flags.h b/includes/rts/Flags.h
index 6487947749..723d8d0c17 100644
--- a/includes/rts/Flags.h
+++ b/includes/rts/Flags.h
@@ -187,6 +187,17 @@ typedef struct _CONCURRENT_FLAGS {
  */
 #define DEFAULT_TICK_INTERVAL USToTime(10000)
 
+/*
+ * When linkerAlwaysPic is true, the runtime linker assume that all object
+ * files were compiled with -fPIC -fexternal-dynamic-refs and load them
+ * anywhere in the address space.
+ */
+#if defined(x86_64_HOST_ARCH) && defined(darwin_HOST_OS)
+#define DEFAULT_LINKER_ALWAYS_PIC true
+#else
+#define DEFAULT_LINKER_ALWAYS_PIC false
+#endif
+
 /* See Note [Synchronization of flags and base APIs] */
 typedef struct _MISC_FLAGS {
     Time    tickInterval;        /* units: TIME_RESOLUTION */
@@ -196,6 +207,7 @@ typedef struct _MISC_FLAGS {
     bool generate_stack_trace;
     bool machineReadable;
     bool internalCounters;       /* See Note [Internal Counter Stats] */
+    bool linkerAlwaysPic;        /* Assume the object code is always PIC */
     StgWord linkerMemBase;       /* address to ask the OS for memory
                                   * for the linker, NULL ==> off */
 } MISC_FLAGS;