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

Summary:
This re-applies {D5195} with fixes for i386:
* Fix unused label warnings, see {D5230} or {D5273}
* Fix a silly bug introduced by moving `#if`

{P190}

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:
See {D5195}, also test under i386:

```
$ uname -a
Linux watashi-arch32 4.18.5-arch1-1.0-ARCH #1 SMP PREEMPT Tue Aug 28
20:45:30 CEST 2018 i686 GNU/Linux
$ cd testsuite/tests/th/ && make test
...
```

will run `./validate` on stacked diff.

Reviewers: simonmar, bgamari, alpmestan, trommler, hvr, erikd

Reviewed By: simonmar

Subscribers: rwbarton, carter

Differential Revision: https://phabricator.haskell.org/D5289

1 files changed, 4 insertions, 21 deletions

diff --git a/rts/linker/Elf.c b/rts/linker/Elf.c
index 9ea10d443f..ae85d73170 100644
--- a/rts/linker/Elf.c
+++ b/rts/linker/Elf.c
@@ -169,6 +169,8 @@ 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)");
@@ -318,6 +320,7 @@ ocDeinit_ELF(ObjectCode * oc)
         }
 
         stgFree(oc->info);
+        oc->info = NULL;
     }
 }
 
@@ -754,7 +757,7 @@ ocGetNames_ELF ( ObjectCode* oc )
           start = mem;
           mapped_start = mem;
 #else
-          if (USE_CONTIGUOUS_MMAP) {
+          if (USE_CONTIGUOUS_MMAP || RtsFlags.MiscFlags.linkerAlwaysPic) {
               // already mapped.
               start = oc->image + offset;
               alloc = SECTION_NOMEM;
@@ -1585,9 +1588,6 @@ 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 =
@@ -1604,7 +1604,6 @@ do_Elf_Rela_relocations ( ObjectCode* oc, char* ehdrC,
           }
           Elf64_Sword payload = off;
           memcpy((void*)P, &payload, sizeof(payload));
-#endif
           break;
       }
 
@@ -1617,9 +1616,6 @@ 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)
@@ -1635,15 +1631,11 @@ 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)
@@ -1659,7 +1651,6 @@ 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:
@@ -1681,9 +1672,6 @@ 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 */
@@ -1701,16 +1689,12 @@ 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)
@@ -1725,7 +1709,6 @@ do_Elf_Rela_relocations ( ObjectCode* oc, char* ehdrC,
           }
           Elf64_Sword payload = off;
           memcpy((void*)P, &payload, sizeof(payload));
-#endif
           break;
       }
 #endif