MC: Calculate intra-section symbol differences correctly for COFF

This fixes PR22060.

llvm-svn: 228565

2 files changed, 36 insertions, 6 deletions

diff --git a/llvm/lib/MC/WinCOFFObjectWriter.cpp b/llvm/lib/MC/WinCOFFObjectWriter.cpp
index bd750af5de4..e3985815e45 100644
--- a/llvm/lib/MC/WinCOFFObjectWriter.cpp
+++ b/llvm/lib/MC/WinCOFFObjectWriter.cpp
@@ -706,17 +706,22 @@ void WinCOFFObjectWriter::RecordRelocation(
     CrossSection = &Symbol.getSection() != &B->getSection();
 
     // Offset of the symbol in the section
-    int64_t a = Layout.getSymbolOffset(&B_SD);
+    int64_t OffsetOfB = Layout.getSymbolOffset(&B_SD);
 
-    // Offset of the relocation in the section
-    int64_t b = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
-
-    FixedValue = b - a;
     // In the case where we have SymbA and SymB, we just need to store the delta
     // between the two symbols.  Update FixedValue to account for the delta, and
     // skip recording the relocation.
-    if (!CrossSection)
+    if (!CrossSection) {
+      int64_t OffsetOfA = Layout.getSymbolOffset(&A_SD);
+      FixedValue = (OffsetOfA - OffsetOfB) + Target.getConstant();
       return;
+    }
+
+    // Offset of the relocation in the section
+    int64_t OffsetOfRelocation =
+        Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
+
+    FixedValue = OffsetOfRelocation - OffsetOfB;
   } else {
     FixedValue = Target.getConstant();
   }
diff --git a/llvm/test/MC/COFF/diff.s b/llvm/test/MC/COFF/diff.s
index 820272a40bf..5111600c744 100644
--- a/llvm/test/MC/COFF/diff.s
+++ b/llvm/test/MC/COFF/diff.s
@@ -1,5 +1,23 @@
 // RUN: llvm-mc -filetype=obj -triple i686-pc-mingw32 %s | llvm-readobj -s -sr -sd | FileCheck %s
 
+.section baz, "xr"
+	.def	X
+	.scl	2;
+	.type	32;
+	.endef
+	.globl	X
+X:
+	mov	Y-X+42,	%eax
+	retl
+
+	.def	Y
+	.scl	2;
+	.type	32;
+	.endef
+	.globl	Y
+Y:
+	retl
+
 	.def	 _foobar;
 	.scl	2;
 	.type	32;
@@ -30,3 +48,10 @@ _rust_crate:
 // CHECK:        SectionData (
 // CHECK-NEXT:     0000: 00000000 00000000 1C000000 20000000
 // CHECK-NEXT:   )
+
+// CHECK:        Name: baz
+// CHECK:        Relocations [
+// CHECK-NEXT:   ]
+// CHECK:        SectionData (
+// CHECK-NEXT:     0000: A1300000 00C3C3
+// CHECK-NEXT:   )