Make sure to include the constant offset when creating a cross-section relative relocation.

[AndyAyers]

Summary

If an initializer expression is of the form &A - &B + C, where A and B are symbols and C is a constant, and A and B are in different coff sections, the value C is lost when translating this to a relocation.

[majnemer]

LGTM

llvm/trunk/lib/MC/WinCOFFObjectWriter.cpp

if (!CrossSection) {
       FixedValue = (OffsetOfA - OffsetOfB) + Target.getConstant();
       return;
     }
 
     // Offset of the relocation in the section
     int64_t OffsetOfRelocation =
         Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
 
-    FixedValue = OffsetOfRelocation - OffsetOfB;
+    FixedValue = (OffsetOfRelocation - OffsetOfB) + Target.getConstant();
   } else {
     FixedValue = Target.getConstant();
   }
 
   COFFRelocation Reloc;
 
   Reloc.Data.SymbolTableIndex = 0;
   Reloc.Data.VirtualAddress = Layout.getFragmentOffset(Fragment);

llvm/trunk/test/MC/COFF/cross-section-relative.ll

+; Verify the assembler produces the expected expressions
+; RUN: llc -mtriple=x86_64-pc-win32 %s -o - | FileCheck %s
+; Verify the .fix data section conveys the right offsets and the right relocations
+; RUN: llc -mtriple=x86_64-pc-win32 -filetype=obj %s -o - | llvm-readobj -relocations -expand-relocs -sections -section-data | FileCheck %s --check-prefix=READOBJ
+
+;;;; some globals
+
+@g1 = constant i32 1;
+@g2 = constant i32 2;
+@g3 = constant i32 3;
+@g4 = constant i32 4;
+@__ImageBase = external global i64*;
+
+;;;; cross-section relative relocations
+
+; CHECK: .quad (g3-t1)+4
+@t1 = global i64 add(i64 sub(i64 ptrtoint(i32* @g3 to i64), i64 ptrtoint(i64* @t1 to i64)), i64 4), section ".fix"
+; CHECK: .quad g3-t2
+@t2 = global i64 sub(i64 ptrtoint(i32* @g3 to i64), i64 ptrtoint(i64* @t2 to i64)), section ".fix"
+; CHECK: .quad (g3-t3)-4
+@t3 = global i64 sub(i64 sub(i64 ptrtoint(i32* @g3 to i64), i64 ptrtoint(i64* @t3 to i64)), i64 4), section ".fix"
+; CHECK: .long g3-t4
+@t4 = global i32 trunc(i64 sub(i64 ptrtoint(i32* @g3 to i64), i64 ptrtoint(i32* @t4 to i64)) to i32), section ".fix"
+
+;;;; image base relocation
+
+; CHECK: .long g3@IMGREL
+@t5 = global i32 trunc(i64 sub(i64 ptrtoint(i32* @g3 to i64), i64 ptrtoint(i64** @__ImageBase to i64)) to i32), section ".fix"
+
+;;;; cross-section relative with source offset
+
+%struct.EEType = type { [2 x i8], i64, i32}
+
+; CHECK: .long g3-(t6+16)
+@t6 = global %struct.EEType { 
+        [2 x i8] c"\01\02", 
+        i64 256,
+        i32 trunc(i64 sub(i64 ptrtoint(i32* @g3 to i64), i64 ptrtoint(i32* getelementptr inbounds (%struct.EEType, %struct.EEType* @t6, i32 0, i32 2) to i64)) to i32 )
+}, section ".fix"
+
+; READOBJ:  Section {
+; READOBJ:    Number: 5
+; READOBJ:    Name: .fix (2E 66 69 78 00 00 00 00)
+; READOBJ:    VirtualSize: 0x0
+; READOBJ:    VirtualAddress: 0x0
+; READOBJ:    RawDataSize: 56
+; READOBJ:    PointerToRawData: 0xEC
+; READOBJ:    PointerToRelocations: 0x124
+; READOBJ:    PointerToLineNumbers: 0x0
+; READOBJ:    RelocationCount: 6
+; READOBJ:    LineNumberCount: 0
+; READOBJ:    Characteristics [ (0xC0500040)
+; READOBJ:      IMAGE_SCN_ALIGN_16BYTES (0x500000)
+; READOBJ:      IMAGE_SCN_CNT_INITIALIZED_DATA (0x40)
+; READOBJ:      IMAGE_SCN_MEM_READ (0x40000000)
+; READOBJ:      IMAGE_SCN_MEM_WRITE (0x80000000)
+; READOBJ:    ]
+; READOBJ:    SectionData (
+; READOBJ:      0000: 10000000 00000000 0C000000 00000000  |................|
+; READOBJ:      0010: 08000000 00000000 0C000000 00000000  |................|
+; READOBJ:      0020: 01020000 00000000 00010000 00000000  |................|
+; READOBJ:      0030: 0C000000 00000000                    |........|
+; READOBJ:    )
+; READOBJ:  }
+; READOBJ:  ]
+; READOBJ:  Relocations [
+; READOBJ:  Section (5) .fix {
+; READOBJ:    Relocation {
+; READOBJ:      Offset: 0x0
+; READOBJ:      Type: IMAGE_REL_AMD64_REL32 (4)
+; READOBJ:      Symbol: .rdata
+; READOBJ:    }
+; READOBJ:    Relocation {
+; READOBJ:      Offset: 0x8
+; READOBJ:      Type: IMAGE_REL_AMD64_REL32 (4)
+; READOBJ:      Symbol: .rdata
+; READOBJ:    }
+; READOBJ:    Relocation {
+; READOBJ:      Offset: 0x10
+; READOBJ:      Type: IMAGE_REL_AMD64_REL32 (4)
+; READOBJ:      Symbol: .rdata
+; READOBJ:    }
+; READOBJ:    Relocation {
+; READOBJ:      Offset: 0x18
+; READOBJ:      Type: IMAGE_REL_AMD64_REL32 (4)
+; READOBJ:      Symbol: .rdata
+; READOBJ:    }
+; READOBJ:    Relocation {
+; READOBJ:      Offset: 0x1C
+; READOBJ:      Type: IMAGE_REL_AMD64_ADDR32NB (3)
+; READOBJ:      Symbol: g3
+; READOBJ:    }
+; READOBJ:    Relocation {
+; READOBJ:      Offset: 0x30
+; READOBJ:      Type: IMAGE_REL_AMD64_REL32 (4)
+; READOBJ:      Symbol: .rdata
+; READOBJ:    }