[lld][MachO] Fix LC_SEGEMENT[_64] filesize computation in -r mode.

Using vmsize to populate this file works when outputing MachO images, but fails
when outputting relocatable objects. This patch fixes the computation to use
file offsets, which works for both output types.

Fixes <rdar://problem/27727666>

llvm-svn: 278297

lld/lib/ReaderWriter/MachO/MachONormalizedFileBinaryWriter.cpp

@@ -643,7 +643,9 @@ llvm::Error MachOFileLayout::writeSingleSegmentLoadCommand(uint8_t *&lc) {
   seg->vmsize = _file.sections.back().address
               + _file.sections.back().content.size();
   seg->fileoff = _endOfLoadCommands;
-  seg->filesize = seg->vmsize;
+  seg->filesize = _sectInfo[&_file.sections.back()].fileOffset +
+                  _file.sections.back().content.size() -
+                  _sectInfo[&_file.sections.front()].fileOffset;
   seg->maxprot = VM_PROT_READ|VM_PROT_WRITE|VM_PROT_EXECUTE;
   seg->initprot = VM_PROT_READ|VM_PROT_WRITE|VM_PROT_EXECUTE;
   seg->nsects = _file.sections.size();

lld/test/mach-o/lc_segment_filesize.yaml

@@ -0,0 +1,31 @@
+# RUN: lld -flavor darwin -arch x86_64 -r -o %t %s && llvm-objdump -private-headers %t | FileCheck %s
+
+# CHECK: filesize 19
+
+--- !mach-o
+arch:            x86_64
+file-type:       MH_OBJECT
+flags:           [ MH_SUBSECTIONS_VIA_SYMBOLS ]
+sections:
+  - segment:         __TEXT
+    section:         __text
+    type:            S_REGULAR
+    attributes:      [ S_ATTR_PURE_INSTRUCTIONS ]
+    alignment:       16
+    address:         0x0000000000000000
+    content:         [ 0x00, 0x00, 0x00 ]
+  - segment:         __TEXT
+    section:         __alt
+    type:            S_REGULAR
+    attributes:      [ S_ATTR_PURE_INSTRUCTIONS ]
+    alignment:       16
+    address:         0x0000000000000010
+    content:         [ 0x00, 0x00, 0x00 ]
+global-symbols:
+  - name:            _main
+    type:            N_SECT
+    scope:           [ N_EXT ]
+    sect:            1
+    value:           0x0000000000000000
+page-size:       0x00000000
+...