[PATCH] D96234: [MC][WebAssembly] Fix provisional values for data alias relocations

[Sam Clegg via Phabricator via llvm-commits]

sbc100 created this revision.
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When calculating the symbol offsets to write as provisitonal values
in object files we are only interested in the offset of the symbol
itself.  For aliases this offset already includes the offset of the
base symbol.

The testin question was added back in https://reviews.llvm.org/D87407
but I believe the expectations here were incorrect.   sym_a lives
at offset 4 and sym_b lives 4 bytes into that (should be 8).

The addresses of the 3 symbosl in this object file are:

foo  : 0
sym_a: 4
sym_b: 8


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D96234

Files:
  llvm/lib/MC/WasmObjectWriter.cpp
  llvm/test/MC/WebAssembly/alias-offset.s


Index: llvm/test/MC/WebAssembly/alias-offset.s
===================================================================
--- llvm/test/MC/WebAssembly/alias-offset.s
+++ llvm/test/MC/WebAssembly/alias-offset.s
@@ -27,8 +27,8 @@
 
 # CHECK-LABEL: <main>:
 # CHECK-EMPTY:
-# CHECK-NEXT:       3: 41 88 80 80 80 00     i32.const       8
+# CHECK-NEXT:       3: 41 84 80 80 80 00     i32.const       4
 # CHECK-NEXT:                        00000004:  R_WASM_MEMORY_ADDR_SLEB      sym_a+0
-# CHECK-NEXT:       9: 36 02 8c 80 80 80 00  i32.store       12
+# CHECK-NEXT:       9: 36 02 88 80 80 80 00  i32.store       8
 # CHECK-NEXT:                        0000000b:  R_WASM_MEMORY_ADDR_LEB      sym_b+0
 # CHECK-NEXT:      10: 0b            end
Index: llvm/lib/MC/WasmObjectWriter.cpp
===================================================================
--- llvm/lib/MC/WasmObjectWriter.cpp
+++ llvm/lib/MC/WasmObjectWriter.cpp
@@ -610,16 +610,13 @@
   case wasm::R_WASM_MEMORY_ADDR_I64:
   case wasm::R_WASM_MEMORY_ADDR_TLS_SLEB: {
     // Provisional value is address of the global plus the offset
-    const MCSymbolWasm *Base =
-        cast<MCSymbolWasm>(Layout.getBaseSymbol(*RelEntry.Symbol));
     // For undefined symbols, use zero
-    if (!Base->isDefined())
+    if (!RelEntry.Symbol->isDefined())
       return 0;
-    const wasm::WasmDataReference &BaseRef = DataLocations[Base],
-                                  &SymRef = DataLocations[RelEntry.Symbol];
-    const WasmDataSegment &Segment = DataSegments[BaseRef.Segment];
+    const wasm::WasmDataReference &SymRef = DataLocations[RelEntry.Symbol];
+    const WasmDataSegment &Segment = DataSegments[SymRef.Segment];
     // Ignore overflow. LLVM allows address arithmetic to silently wrap.
-    return Segment.Offset + BaseRef.Offset + SymRef.Offset + RelEntry.Addend;
+    return Segment.Offset + SymRef.Offset + RelEntry.Addend;
   }
   default:
     llvm_unreachable("invalid relocation type");


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