Fix incorrect calculated relocations on Windows x86_64

Summary:
See #12031 for analysis, but essentially what happens is:

To sum up the issue, the reason this seems to go wrong is because
of how we initialize the `.bss` section for Windows in the runtime linker.

The first issue is where we calculate the zero space for the section:

```
zspace = stgCallocBytes(1, bss_sz, "ocGetNames_PEi386(anonymous bss)");
sectab_i->PointerToRawData = ((UChar*)zspace) - ((UChar*)(oc->image));
```

Where
```
UInt32 PointerToRawData;
```

This means we're stuffing a `64-bit` value into a `32-bit` one. Also `zspace`
can be larger than `oc->image`. In which case it'll overflow and
then get truncated in the cast.

The address of a value in the `.bss` section is then calculated as:

```
addr = ((UChar*)(oc->image))
     + (sectabent->PointerToRawData
     + symtab_i->Value);
```

If it does truncate then this calculation won't be correct (which is what is happening).

We then later use the value of `addr` as the `S` (Symbol) value for the relocations

```
S = (size_t) lookupSymbol_( (char*)symbol );
```

Now the majority of the relocations are `R_X86_64_PC32` etc.
e.g. They are guaranteed to fit in a `32-bit` value.

The `R_X86_64_64` introduced for these pseudo-relocations so they can use
the full `48-bit` addressing space isn't as lucky.
As for why it sometimes work has to do on whether the value is truncated or not.

`PointerToRawData` can't be changed because it's size is fixed by the PE specification.

Instead just like with the other platforms, we now use `section` on Windows as well.
This gives us a `start` parameter of type `void*` which solves the issue.

This refactors the code to use `section.start` and to fix the issues.

Test Plan: ./validate and new test added T12031

Reviewers: RyanGlScott, erikd, bgamari, austin, simonmar

Reviewed By: simonmar

Subscribers: thomie, #ghc_windows_task_force

Differential Revision: https://phabricator.haskell.org/D2316

GHC Trac Issues: #12031, #11317

7 files changed, 53 insertions, 0 deletions

diff --git a/testsuite/tests/rts/T12031/ExternBug.hs b/testsuite/tests/rts/T12031/ExternBug.hs
new file mode 100644
index 0000000000..5c28aede00
--- /dev/null
+++ b/testsuite/tests/rts/T12031/ExternBug.hs
@@ -0,0 +1,9 @@
+-- Copyright (c) 2016, Ryan Scott
+-- ExternBug.hs
+{-# LANGUAGE ForeignFunctionInterface #-}
+module ExternBug (bar) where
+
+{-# INCLUDE foo.h #-}
+
+foreign import ccall "bar"
+  bar :: IO ()
diff --git a/testsuite/tests/rts/T12031/Makefile b/testsuite/tests/rts/T12031/Makefile
new file mode 100644
index 0000000000..0a9420692a
--- /dev/null
+++ b/testsuite/tests/rts/T12031/Makefile
@@ -0,0 +1,8 @@
+TOP=../../..
+include $(TOP)/mk/boilerplate.mk
+include $(TOP)/mk/test.mk
+
+T12031:
+	'$(TEST_HC)' -c bar.c -o bar.o
+	'$(TEST_HC)' -c baz.c -o baz.o
+	echo bar | '$(TEST_HC)' $(TEST_HC_OPTS_INTERACTIVE) bar.o baz.o ExternBug.hs
diff --git a/testsuite/tests/rts/T12031/T12031.stdout b/testsuite/tests/rts/T12031/T12031.stdout
new file mode 100644
index 0000000000..e5cc126783
--- /dev/null
+++ b/testsuite/tests/rts/T12031/T12031.stdout
@@ -0,0 +1 @@
+The value of foo is 1
diff --git a/testsuite/tests/rts/T12031/all.T b/testsuite/tests/rts/T12031/all.T
new file mode 100644
index 0000000000..b051514109
--- /dev/null
+++ b/testsuite/tests/rts/T12031/all.T
@@ -0,0 +1,4 @@
+test('T12031', [ extra_clean(['bar.o', 'baz.o', 'ExternBug.o'])
+               , extra_files(['bar.c', 'baz.c', 'ExternBug.hs', 'foo.h'])
+               ],
+               run_command, ['$MAKE -s --no-print-directory T12031'])
diff --git a/testsuite/tests/rts/T12031/bar.c b/testsuite/tests/rts/T12031/bar.c
new file mode 100644
index 0000000000..257cc198f4
--- /dev/null
+++ b/testsuite/tests/rts/T12031/bar.c
@@ -0,0 +1,11 @@
+// Copyright (c) 2016, Ryan Scott
+// bar.c
+#include "foo.h"
+
+int foo = 0;
+
+void bar(void) {
+    foo = 1;
+
+    baz();
+}
diff --git a/testsuite/tests/rts/T12031/baz.c b/testsuite/tests/rts/T12031/baz.c
new file mode 100644
index 0000000000..d710148736
--- /dev/null
+++ b/testsuite/tests/rts/T12031/baz.c
@@ -0,0 +1,9 @@
+// Copyright (c) 2016, Ryan Scott
+// baz.c
+#include "foo.h"
+#include <stdio.h>
+
+void baz(void) {
+    printf("The value of foo is %d\n", foo); // Segfaults on this line
+    fflush(stdout);
+}
diff --git a/testsuite/tests/rts/T12031/foo.h b/testsuite/tests/rts/T12031/foo.h
new file mode 100644
index 0000000000..d3ca4aad2d
--- /dev/null
+++ b/testsuite/tests/rts/T12031/foo.h
@@ -0,0 +1,11 @@
+// Copyright (c) 2016, Ryan Scott
+// foo.h
+#ifndef FOO_H
+#define FOO_H
+
+extern int foo;
+
+void bar(void);
+void baz(void);
+
+#endif