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

This reverts commit cb3f710d952c0a2bad539f76c2ab6d07ba894bea.

8 files changed, 73 insertions, 121 deletions

diff --git a/docs/users_guide/runtime_control.rst b/docs/users_guide/runtime_control.rst
index 0048a51837..a5c2f1474f 100644
--- a/docs/users_guide/runtime_control.rst
+++ b/docs/users_guide/runtime_control.rst
@@ -241,28 +241,6 @@ Miscellaneous RTS options
     crashes if exception handling are enabled. In order to get more information
     in compiled executables, C code or DLLs symbols need to be available.
 
-
-.. rts-flag:: -xp
-
-    On 64-bit machines, the runtime linker usually needs to map object code
-    into the low 2Gb of the address space, due to the x86_64 small memory model
-    where most symbol references are 32 bits. The problem is that this 2Gb of
-    address space can fill up, especially if you're loading a very large number
-    of object files into GHCi.
-
-    This flag offers a workaround, albeit a slightly convoluted one. To be able
-    to load an object file outside of the low 2Gb, the object code needs to be
-    compiled with ``-fPIC -fexternal-dynamic-refs``. When the ``+RTS -xp`` flag
-    is passed, the linker will assume that all object files were compiled with
-    ``-fPIC -fexternal-dynamic-refs`` and load them anywhere in the address
-    space. It's up to you to arrange that the object files you load (including
-    all packages) were compiled in the right way. If this is not the case for
-    an object, the linker will probably fail with an error message when the
-    problem is detected.
-
-    On some platforms where PIC is always the case, e.g. x86_64 MacOS X, this
-    flag is enabled by default.
-
 .. rts-flag:: -xm ⟨address⟩
 
     .. index::
@@ -272,10 +250,8 @@ Miscellaneous RTS options
 
         This option is for working around memory allocation
         problems only. Do not use unless GHCi fails with a message like
-        “\ ``failed to mmap() memory below 2Gb``\ ”. Consider recompiling
-        the objects with ``-fPIC -fexternal-dynamic-refs`` and using the
-        ``-xp`` flag instead. If you need to use this option to get GHCi
-        working on your machine, please file a bug.
+        “\ ``failed to mmap() memory below 2Gb``\ ”. If you need to use this
+        option to get GHCi working on your machine, please file a bug.
 
     On 64-bit machines, the RTS needs to allocate memory in the low 2Gb
     of the address space. Support for this across different operating
diff --git a/includes/rts/Flags.h b/includes/rts/Flags.h
index 3582e6abde..63450d5ece 100644
--- a/includes/rts/Flags.h
+++ b/includes/rts/Flags.h
@@ -188,17 +188,6 @@ 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 */
@@ -208,7 +197,6 @@ 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;
diff --git a/libraries/base/GHC/RTS/Flags.hsc b/libraries/base/GHC/RTS/Flags.hsc
index 249bcd5a98..12cb828e6a 100644
--- a/libraries/base/GHC/RTS/Flags.hsc
+++ b/libraries/base/GHC/RTS/Flags.hsc
@@ -139,7 +139,6 @@ data MiscFlags = MiscFlags
     , generateStackTrace    :: Bool
     , machineReadable       :: Bool
     , internalCounters      :: Bool
-    , linkerAlwaysPic       :: Bool
     , linkerMemBase         :: Word
       -- ^ address to ask the OS for memory for the linker, 0 ==> off
     } deriving ( Show -- ^ @since 4.8.0.0
@@ -445,8 +444,6 @@ getMiscFlags = do
                   (#{peek MISC_FLAGS, machineReadable} ptr :: IO CBool))
             <*> (toBool <$>
                   (#{peek MISC_FLAGS, internalCounters} ptr :: IO CBool))
-            <*> (toBool <$>
-                  (#{peek MISC_FLAGS, linkerAlwaysPic} ptr :: IO CBool))
             <*> #{peek MISC_FLAGS, linkerMemBase} ptr
 
 getDebugFlags :: IO DebugFlags
diff --git a/rts/Linker.c b/rts/Linker.c
index 05f40b6e7f..4c69d0832e 100644
--- a/rts/Linker.c
+++ b/rts/Linker.c
@@ -74,6 +74,10 @@
 #  include <mach-o/fat.h>
 #endif
 
+#if defined(x86_64_HOST_ARCH) && defined(darwin_HOST_OS)
+#define ALWAYS_PIC
+#endif
+
 #if defined(dragonfly_HOST_OS)
 #include <sys/tls.h>
 #endif
@@ -199,7 +203,9 @@ static void freeNativeCode_ELF (ObjectCode *nc);
  * We pick a default address based on the OS, but also make this
  * configurable via an RTS flag (+RTS -xm)
  */
-#if defined(MAP_32BIT) || DEFAULT_LINKER_ALWAYS_PIC
+#if !defined(ALWAYS_PIC) && defined(x86_64_HOST_ARCH)
+
+#if defined(MAP_32BIT)
 // Try to use MAP_32BIT
 #define MMAP_32BIT_BASE_DEFAULT 0
 #else
@@ -208,6 +214,7 @@ static void freeNativeCode_ELF (ObjectCode *nc);
 #endif
 
 static void *mmap_32bit_base = (void *)MMAP_32BIT_BASE_DEFAULT;
+#endif
 
 static void ghciRemoveSymbolTable(HashTable *table, const SymbolName* key,
     ObjectCode *owner)
@@ -478,10 +485,12 @@ initLinker_ (int retain_cafs)
     }
 #   endif
 
+#if !defined(ALWAYS_PIC) && defined(x86_64_HOST_ARCH)
     if (RtsFlags.MiscFlags.linkerMemBase != 0) {
         // User-override for mmap_32bit_base
         mmap_32bit_base = (void*)RtsFlags.MiscFlags.linkerMemBase;
     }
+#endif
 
     if (RTS_LINKER_USE_MMAP)
         m32_allocator_init();
@@ -1009,30 +1018,29 @@ mmapForLinker (size_t bytes, uint32_t flags, int fd, int offset)
    void *map_addr = NULL;
    void *result;
    size_t size;
-   uint32_t tryMap32Bit = RtsFlags.MiscFlags.linkerAlwaysPic
-     ? 0
-     : TRY_MAP_32BIT;
    static uint32_t fixed = 0;
 
    IF_DEBUG(linker, debugBelch("mmapForLinker: start\n"));
    size = roundUpToPage(bytes);
 
+#if !defined(ALWAYS_PIC) && defined(x86_64_HOST_ARCH)
 mmap_again:
 
    if (mmap_32bit_base != 0) {
        map_addr = mmap_32bit_base;
    }
+#endif
 
    IF_DEBUG(linker,
             debugBelch("mmapForLinker: \tprotection %#0x\n",
                        PROT_EXEC | PROT_READ | PROT_WRITE));
    IF_DEBUG(linker,
             debugBelch("mmapForLinker: \tflags      %#0x\n",
-                       MAP_PRIVATE | tryMap32Bit | fixed | flags));
+                       MAP_PRIVATE | TRY_MAP_32BIT | fixed | flags));
 
    result = mmap(map_addr, size,
                  PROT_EXEC|PROT_READ|PROT_WRITE,
-                 MAP_PRIVATE|tryMap32Bit|fixed|flags, fd, offset);
+                 MAP_PRIVATE|TRY_MAP_32BIT|fixed|flags, fd, offset);
 
    if (result == MAP_FAILED) {
        sysErrorBelch("mmap %" FMT_Word " bytes at %p",(W_)size,map_addr);
@@ -1040,9 +1048,8 @@ mmap_again:
        return NULL;
    }
 
-#if defined(x86_64_HOST_ARCH)
-   if (RtsFlags.MiscFlags.linkerAlwaysPic) {
-   } else if (mmap_32bit_base != 0) {
+#if !defined(ALWAYS_PIC) && defined(x86_64_HOST_ARCH)
+   if (mmap_32bit_base != 0) {
        if (result == map_addr) {
            mmap_32bit_base = (StgWord8*)map_addr + size;
        } else {
@@ -1222,10 +1229,10 @@ void freeObjectCode (ObjectCode *oc)
 #if defined(NEED_SYMBOL_EXTRAS) && (!defined(x86_64_HOST_ARCH) \
                                     || !defined(mingw32_HOST_OS))
     if (RTS_LINKER_USE_MMAP) {
-      if (!USE_CONTIGUOUS_MMAP && !RtsFlags.MiscFlags.linkerAlwaysPic &&
-          oc->symbol_extras != NULL) {
-        m32_free(oc->symbol_extras, sizeof(SymbolExtra) * oc->n_symbol_extras);
-      }
+        if (!USE_CONTIGUOUS_MMAP && oc->symbol_extras != NULL) {
+            m32_free(oc->symbol_extras,
+                    sizeof(SymbolExtra) * oc->n_symbol_extras);
+        }
     }
     else {
         stgFree(oc->symbol_extras);
diff --git a/rts/RtsFlags.c b/rts/RtsFlags.c
index 37eafa5c55..ff9635ab24 100644
--- a/rts/RtsFlags.c
+++ b/rts/RtsFlags.c
@@ -236,7 +236,6 @@ void initRtsFlagsDefaults(void)
     RtsFlags.MiscFlags.generate_dump_file      = false;
     RtsFlags.MiscFlags.machineReadable         = false;
     RtsFlags.MiscFlags.internalCounters        = false;
-    RtsFlags.MiscFlags.linkerAlwaysPic         = DEFAULT_LINKER_ALWAYS_PIC;
     RtsFlags.MiscFlags.linkerMemBase           = 0;
 
 #if defined(THREADED_RTS)
@@ -458,11 +457,6 @@ usage_text[] = {
 "  -e<n>     Maximum number of outstanding local sparks (default: 4096)",
 #endif
 #if defined(x86_64_HOST_ARCH)
-#if !DEFAULT_LINKER_ALWAYS_PIC
-"  -xp       Assume that all object files were compiled with -fPIC",
-"            -fexternal-dynamic-refs and load them anywhere in the address",
-"            space",
-#endif
 "  -xm       Base address to mmap memory in the GHCi linker",
 "            (hex; must be <80000000)",
 #endif
@@ -1508,11 +1502,6 @@ error = true;
                     break;
 
 #if defined(x86_64_HOST_ARCH)
-                case 'p': /* linkerAlwaysPic */
-                    OPTION_UNSAFE;
-                    RtsFlags.MiscFlags.linkerAlwaysPic = true;
-                    break;
-
                 case 'm': /* linkerMemBase */
                     OPTION_UNSAFE;
                     if (rts_argv[arg][3] != '\0') {
diff --git a/rts/linker/Elf.c b/rts/linker/Elf.c
index 8954d68965..157e43b385 100644
--- a/rts/linker/Elf.c
+++ b/rts/linker/Elf.c
@@ -169,8 +169,6 @@ get_shndx_table(Elf_Ehdr* ehdr)
 void
 ocInit_ELF(ObjectCode * oc)
 {
-    ocDeinit_ELF(oc);
-
     oc->info = (struct ObjectCodeFormatInfo*)stgCallocBytes(
             1, sizeof *oc->info,
             "ocInit_Elf(ObjectCodeFormatInfo)");
@@ -320,7 +318,6 @@ ocDeinit_ELF(ObjectCode * oc)
         }
 
         stgFree(oc->info);
-        oc->info = NULL;
     }
 }
 
@@ -753,7 +750,7 @@ ocGetNames_ELF ( ObjectCode* oc )
           start = mem;
           mapped_start = mem;
 #else
-          if (USE_CONTIGUOUS_MMAP || RtsFlags.MiscFlags.linkerAlwaysPic) {
+          if (USE_CONTIGUOUS_MMAP) {
               // already mapped.
               start = oc->image + offset;
               alloc = SECTION_NOMEM;
@@ -1616,6 +1613,9 @@ do_Elf_Rela_relocations ( ObjectCode* oc, char* ehdrC,
 
       case COMPAT_R_X86_64_PC32:
       {
+#if defined(ALWAYS_PIC)
+          barf("R_X86_64_PC32 relocation, but ALWAYS_PIC.");
+#else
           StgInt64 off = value - P;
           if (off != (Elf64_Sword)off && X86_64_ELF_NONPIC_HACK) {
               StgInt64 pltAddress =
@@ -1632,6 +1632,7 @@ do_Elf_Rela_relocations ( ObjectCode* oc, char* ehdrC,
           }
           Elf64_Sword payload = off;
           memcpy((void*)P, &payload, sizeof(payload));
+#endif
           break;
       }
 
@@ -1644,6 +1645,9 @@ do_Elf_Rela_relocations ( ObjectCode* oc, char* ehdrC,
 
       case COMPAT_R_X86_64_32:
       {
+#if defined(ALWAYS_PIC)
+          barf("R_X86_64_32 relocation, but ALWAYS_PIC.");
+#else
           if (value != (Elf64_Word)value && X86_64_ELF_NONPIC_HACK) {
               StgInt64 pltAddress =
                   (StgInt64) &makeSymbolExtra(oc, ELF_R_SYM(info), S)
@@ -1659,11 +1663,15 @@ do_Elf_Rela_relocations ( ObjectCode* oc, char* ehdrC,
           }
           Elf64_Word payload = value;
           memcpy((void*)P, &payload, sizeof(payload));
+#endif
           break;
       }
 
       case COMPAT_R_X86_64_32S:
       {
+#if defined(ALWAYS_PIC)
+          barf("R_X86_64_32S relocation, but ALWAYS_PIC.");
+#else
           if ((StgInt64)value != (Elf64_Sword)value && X86_64_ELF_NONPIC_HACK) {
               StgInt64 pltAddress =
                   (StgInt64) &makeSymbolExtra(oc, ELF_R_SYM(info), S)
@@ -1679,6 +1687,7 @@ do_Elf_Rela_relocations ( ObjectCode* oc, char* ehdrC,
           }
           Elf64_Sword payload = value;
           memcpy((void*)P, &payload, sizeof(payload));
+#endif
           break;
       }
       case COMPAT_R_X86_64_REX_GOTPCRELX:
@@ -1700,6 +1709,9 @@ do_Elf_Rela_relocations ( ObjectCode* oc, char* ehdrC,
 #if defined(dragonfly_HOST_OS)
       case COMPAT_R_X86_64_GOTTPOFF:
       {
+#if defined(ALWAYS_PIC)
+          barf("R_X86_64_GOTTPOFF relocation, but ALWAYS_PIC.");
+#else
         /* determine the offset of S to the current thread's tls
            area
            XXX: Move this to the beginning of function */
@@ -1717,12 +1729,16 @@ do_Elf_Rela_relocations ( ObjectCode* oc, char* ehdrC,
           }
           Elf64_SWord payload = off;
           memcpy((void*)P, &payload, sizeof(payload));
+#endif
           break;
       }
 #endif
 
       case COMPAT_R_X86_64_PLT32:
       {
+#if defined(ALWAYS_PIC)
+          barf("R_X86_64_PLT32 relocation, but ALWAYS_PIC.");
+#else
           StgInt64 off = value - P;
           if (off != (Elf64_Sword)off) {
               StgInt64 pltAddress = (StgInt64) &makeSymbolExtra(oc, ELF_R_SYM(info), S)
@@ -1737,6 +1753,7 @@ do_Elf_Rela_relocations ( ObjectCode* oc, char* ehdrC,
           }
           Elf64_Sword payload = off;
           memcpy((void*)P, &payload, sizeof(payload));
+#endif
           break;
       }
 #endif
diff --git a/rts/linker/MachO.c b/rts/linker/MachO.c
index de7a156403..8bdf35ee6b 100644
--- a/rts/linker/MachO.c
+++ b/rts/linker/MachO.c
@@ -99,8 +99,6 @@ bool ocMprotect_MachO( ObjectCode *oc );
 void
 ocInit_MachO(ObjectCode * oc)
 {
-    ocDeinit_MachO(oc);
-
     oc->info = (struct ObjectCodeFormatInfo*)stgCallocBytes(
                 1, sizeof *oc->info,
                 "ocInit_MachO(ObjectCodeFormatInfo)");
@@ -162,19 +160,16 @@ ocInit_MachO(ObjectCode * oc)
 
 void
 ocDeinit_MachO(ObjectCode * oc) {
-    if (oc->info != NULL) {
-        if(oc->info->n_macho_symbols > 0) {
-            stgFree(oc->info->macho_symbols);
-        }
+    if(oc->info->n_macho_symbols > 0) {
+        stgFree(oc->info->macho_symbols);
+    }
 #if defined(aarch64_HOST_ARCH)
-        freeGot(oc);
-        for(int i = 0; i < oc->n_sections; i++) {
-            freeStubs(&oc->sections[i]);
-        }
-#endif
-        stgFree(oc->info);
-        oc->info = NULL;
+    freeGot(oc);
+    for(int i = 0; i < oc->n_sections; i++) {
+        freeStubs(&oc->sections[i]);
     }
+#endif
+    stgFree(oc->info);
 }
 
 static int
diff --git a/rts/linker/SymbolExtras.c b/rts/linker/SymbolExtras.c
index 4c40b10877..88541f44d0 100644
--- a/rts/linker/SymbolExtras.c
+++ b/rts/linker/SymbolExtras.c
@@ -19,12 +19,6 @@
 #include "linker/SymbolExtras.h"
 #include "linker/M32Alloc.h"
 
-#if defined(OBJFORMAT_ELF)
-#  include "linker/Elf.h"
-#elif defined(OBJFORMAT_MACHO)
-#  include "linker/MachO.h"
-#endif
-
 #include <string.h>
 #if RTS_LINKER_USE_MMAP
 #include <sys/mman.h>
@@ -52,24 +46,8 @@
 int ocAllocateSymbolExtras( ObjectCode* oc, int count, int first )
 {
   size_t n;
-  void* oldImage = oc->image;
-
-  if (count > 0) {
-    if (!RTS_LINKER_USE_MMAP) {
-
-      // round up to the nearest 4
-      int aligned = (oc->fileSize + 3) & ~3;
-      int misalignment = oc->misalignment;
 
-      oc->image -= misalignment;
-      oc->image = stgReallocBytes( oc->image,
-                               misalignment +
-                               aligned + sizeof (SymbolExtra) * count,
-                               "ocAllocateSymbolExtras" );
-      oc->image += misalignment;
-
-      oc->symbol_extras = (SymbolExtra *) (oc->image + aligned);
-    } else if (USE_CONTIGUOUS_MMAP || RtsFlags.MiscFlags.linkerAlwaysPic) {
+  if (RTS_LINKER_USE_MMAP && USE_CONTIGUOUS_MMAP) {
       n = roundUpToPage(oc->fileSize);
 
       /* Keep image and symbol_extras contiguous */
@@ -85,37 +63,42 @@ int ocAllocateSymbolExtras( ObjectCode* oc, int count, int first )
           oc->imageMapped = true;
           oc->fileSize = n + (sizeof(SymbolExtra) * count);
           oc->symbol_extras = (SymbolExtra *) (oc->image + n);
-          if (mprotect(new, allocated_size,
-                       PROT_READ | PROT_WRITE | PROT_EXEC) != 0) {
-            sysErrorBelch("unable to protect memory");
+          if(mprotect(new, allocated_size, PROT_READ | PROT_EXEC) != 0) {
+              sysErrorBelch("unable to protect memory");
           }
       }
       else {
           oc->symbol_extras = NULL;
           return 0;
       }
-    } else {
+  }
+  else if( count > 0 ) {
+    if (RTS_LINKER_USE_MMAP) {
+        n = roundUpToPage(oc->fileSize);
+
         oc->symbol_extras = m32_alloc(sizeof(SymbolExtra) * count, 8);
         if (oc->symbol_extras == NULL) return 0;
     }
+    else {
+        // round up to the nearest 4
+        int aligned = (oc->fileSize + 3) & ~3;
+        int misalignment = oc->misalignment;
+
+        oc->image -= misalignment;
+        oc->image = stgReallocBytes( oc->image,
+                                 misalignment +
+                                 aligned + sizeof (SymbolExtra) * count,
+                                 "ocAllocateSymbolExtras" );
+        oc->image += misalignment;
+
+        oc->symbol_extras = (SymbolExtra *) (oc->image + aligned);
+    }
   }
 
   if (oc->symbol_extras != NULL) {
       memset( oc->symbol_extras, 0, sizeof (SymbolExtra) * count );
   }
 
-  // ObjectCodeFormatInfo contains computed addresses based on offset to
-  // image, if the address of image changes, we need to invalidate
-  // the ObjectCodeFormatInfo and recompute it.
-  if (oc->image != oldImage) {
-#if defined(OBJFORMAT_MACHO)
-    ocInit_MachO( oc );
-#endif
-#if defined(OBJFORMAT_ELF)
-    ocInit_ELF( oc );
-#endif
-  }
-
   oc->first_symbol_extra = first;
   oc->n_symbol_extras = count;