PECOFF: Fix I386_DIR32 relocation to an absolute symbol

Previously, we incorrectly added the image base address to an absolute
symbol address (that calculation doesn't make any sense) if an
IMAGE_REL_I386_DIR32 relocation is applied to an absolute symbol.

This patch fixes the issue. With this fix, we can link Bochs using LLD.
(Choosing Bochs has no special meaining -- I just picked it up as a
test program and found it didn't work.) This also fixes one of the
issues we currently have to link Chromium using LLD.

llvm-svn: 228279

lld/lib/ReaderWriter/PECOFF/WriterPECOFF.cpp

@@ -647,7 +647,8 @@ void AtomChunk::applyRelocationsX86(uint8_t *buffer,
       auto relocSite32 = reinterpret_cast<ulittle32_t *>(
           buffer + layout->_fileOffset + ref->offsetInAtom());
       auto relocSite16 = reinterpret_cast<ulittle16_t *>(relocSite32);
-      uint64_t targetAddr = atomRva[ref->target()];
+      const Atom *target = ref->target();
+      uint64_t targetAddr = atomRva[target];
       // Also account for whatever offset is already stored at the relocation
       // site.
       switch (ref->kindValue()) {
@@ -656,7 +657,10 @@ void AtomChunk::applyRelocationsX86(uint8_t *buffer,
         break;
       case llvm::COFF::IMAGE_REL_I386_DIR32:
         // Set target's 32-bit VA.
-        *relocSite32 += targetAddr + imageBaseAddress;
+        if (auto *abs = dyn_cast<AbsoluteAtom>(target))
+          *relocSite32 += abs->value();
+        else
+          *relocSite32 += targetAddr + imageBaseAddress;
         break;
       case llvm::COFF::IMAGE_REL_I386_DIR32NB:
         // Set target's 32-bit RVA.

lld/test/pecoff/Inputs/abs.obj.yaml

@@ -0,0 +1,11 @@
+header:
+  Machine:         IMAGE_FILE_MACHINE_I386
+  Characteristics: []
+sections:
+symbols:
+  - Name:            _abs_value
+    Value:           0xDEADBEEF
+    SectionNumber:   -1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL

lld/test/pecoff/Inputs/reloc.obj.yaml

@@ -6,7 +6,7 @@ sections:
   - Name:            .text
     Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
     Alignment:       16
-    SectionData:     68000000006800000000680000000068000000006800000000
+    SectionData:     680000000068000000006800000000680000000068000000006800000000
     Relocations:
       - VirtualAddress:  1
         SymbolName:      _message
@@ -23,6 +23,9 @@ sections:
       - VirtualAddress:  21
         SymbolName:      __imp__MessageBoxA@16
         Type:            IMAGE_REL_I386_DIR32
+      - VirtualAddress:  26
+        SymbolName:      _abs_value
+        Type:            IMAGE_REL_I386_DIR32
   - Name:            .data
     Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_READ, IMAGE_SCN_MEM_WRITE ]
     Alignment:       4
@@ -70,4 +73,10 @@ symbols:
     SimpleType:      IMAGE_SYM_TYPE_NULL
     ComplexType:     IMAGE_SYM_DTYPE_NULL
     StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+  - Name:            _abs_value
+    Value:           0
+    SectionNumber:   0
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
 ...

lld/test/pecoff/reloc.test

@@ -1,9 +1,10 @@
 # REQUIRES: x86
 
-# RUN: yaml2obj %p/Inputs/reloc.obj.yaml > %t.obj
+# RUN: yaml2obj %p/Inputs/reloc.obj.yaml > %t1.obj
+# RUN: yaml2obj %p/Inputs/abs.obj.yaml > %t2.obj
 #
 # RUN: lld -flavor link /out:%t.exe /subsystem:console /force /opt:noref \
-# RUN:   -- %t.obj
+# RUN:   -- %t1.obj %t2.obj
 # RUN: llvm-objdump -d %t.exe | FileCheck %s
 
 CHECK: .text:
@@ -12,3 +13,4 @@ CHECK:    3005: 68 05 00 00 00
 CHECK:    300a: 68 00 10 40 00
 CHECK:    300f: 68 00 10 40 00
 CHECK:    3014: 68 00 20 40 00
+CHECK:    3019: 68 ef be ad de