[WebAssembly] Fixed DWARF DW_AT_low_pc encoded as 64-bit in wasm64

[aardappel]

Summary

Also added general wasm64 DWARF test.
Also added asserts for unsupported reloc combinations that triggered this bug.

[dschuff]

LGTM for now.
As I said, I have a feeling we may need to do something more to get the data address space right. But this is fine to avoid crashing.

llvm/test/MC/WebAssembly/dwarfdump64.ll

1

It might make sense to use the dwarfdump argument --show-form for this test, then we can see which attributes have addr vs other forms.

38

I have a feeling that this is probably wrong (i.e. it's 4 instead of 8). Maybe we should put a TODO here.

[dschuff]

llvm/test/MC/WebAssembly/dwarfdump64.ll

38

(I mean that it's using a 4-byte address instead of an 8-byte. not that the value is wrong)

[aardappel]

updated test for --show-form and added TODO

[aardappel]

The paths in this test only worked on Windows. A fix has been pushed in b093eba08478db387fc2765dee1e1bf2d64fcf68

llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCAsmInfo.cpp

 using namespace llvm;
 
 #define DEBUG_TYPE "wasm-mc-asm-info"
 
 WebAssemblyMCAsmInfo::~WebAssemblyMCAsmInfo() = default; // anchor.
 
 WebAssemblyMCAsmInfo::WebAssemblyMCAsmInfo(const Triple &T,
                                            const MCTargetOptions &Options) {
-  CodePointerSize = CalleeSaveStackSlotSize = T.isArch64Bit() ? 8 : 4;
+  CalleeSaveStackSlotSize = T.isArch64Bit() ? 8 : 4;
+  // So far this is used for DWARF DW_AT_low_pc which is always 32-bit in Wasm.
+  CodePointerSize = 4;
 
   // TODO: What should MaxInstLength be?
 
   UseDataRegionDirectives = true;
 
   // Use .skip instead of .zero because .zero is confusing when used with two
   // arguments (it doesn't actually zero things out).
   ZeroDirective = "\t.skip\t";

llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyWasmObjectWriter.cpp

if (auto Section = static_cast<const MCSectionWasm *>(
         return wasm::R_WASM_FUNCTION_OFFSET_I32;
       else if (!Section->isWasmData())
         return wasm::R_WASM_SECTION_OFFSET_I32;
     }
     return wasm::R_WASM_MEMORY_ADDR_I32;
   case FK_Data_8:
     if (SymA.isFunction())
       return wasm::R_WASM_TABLE_INDEX_I64;
+    if (SymA.isGlobal())
+      llvm_unreachable("unimplemented R_WASM_GLOBAL_INDEX_I64");
+    if (auto Section = static_cast<const MCSectionWasm *>(
+            getFixupSection(Fixup.getValue()))) {
+      if (Section->getKind().isText())
+        llvm_unreachable("unimplemented R_WASM_FUNCTION_OFFSET_I64");
+      else if (!Section->isWasmData())
+        llvm_unreachable("unimplemented R_WASM_SECTION_OFFSET_I64");
+    }
     assert(SymA.isData());
     return wasm::R_WASM_MEMORY_ADDR_I64;
   default:
     llvm_unreachable("unimplemented fixup kind");
   }
 }
 
 std::unique_ptr<MCObjectTargetWriter>
 llvm::createWebAssemblyWasmObjectWriter(bool Is64Bit, bool IsEmscripten) {
   return std::make_unique<WebAssemblyWasmObjectWriter>(Is64Bit, IsEmscripten);
 }

llvm/test/MC/WebAssembly/dwarfdump64.ll

+; RUN: llc -filetype=obj %s -o - | llvm-dwarfdump - | FileCheck %s
+
+; CHECK: .debug_info contents:
+; CHECK-NEXT: 0x00000000: Compile Unit: length = 0x0000006e, format = DWARF32, version = 0x0004, abbr_offset = 0x0000, addr_size = 0x04 (next unit at 0x00000072)
+
+; CHECK: 0x0000000b: DW_TAG_compile_unit
+; CHECK-NEXT:              DW_AT_producer ("clang version 6.0.0 (trunk 315924) (llvm/trunk 315960)")
+; CHECK-NEXT:              DW_AT_language (DW_LANG_C99)
+; CHECK-NEXT:              DW_AT_name ("test.c")
+; CHECK-NEXT:              DW_AT_stmt_list  (0x00000000)
+; CHECK-NEXT:              DW_AT_comp_dir ("/usr/local/google/home/sbc/dev/wasm/simple")
+; CHECK-NEXT:              DW_AT_GNU_pubnames (true)
+; CHECK-NEXT:              DW_AT_low_pc   (0x00000002)
+; CHECK-NEXT:              DW_AT_high_pc  (0x00000004)
+
+; CHECK: 0x00000026:   DW_TAG_variable
+; CHECK-NEXT:                DW_AT_name ("foo")
+; CHECK-NEXT:                DW_AT_type (0x00000037 "int*")
+; CHECK-NEXT:                DW_AT_external (true)
+; CHECK-NEXT:                DW_AT_decl_file  ("/usr/local/google/home/sbc/dev/wasm/simple{{[/\\]}}test.c")
+; CHECK-NEXT:                DW_AT_decl_line  (4)
+; CHECK-NEXT:                DW_AT_location (DW_OP_addr 0x0)
+
+; CHECK: 0x00000037:   DW_TAG_pointer_type
+; CHECK-NEXT:                DW_AT_type (0x0000003c "int")
+
+; CHECK: 0x0000003c:   DW_TAG_base_type
+; CHECK-NEXT:                DW_AT_name ("int")
+; CHECK-NEXT:                DW_AT_encoding (DW_ATE_signed)
+; CHECK-NEXT:                DW_AT_byte_size  (0x04)
+
+; CHECK: 0x00000043:   DW_TAG_variable
+; CHECK-NEXT:                DW_AT_name ("ptr2")
+; CHECK-NEXT:                DW_AT_type (0x00000054 "void()*")
+; CHECK-NEXT:                DW_AT_external (true)
+; CHECK-NEXT:                DW_AT_decl_file  ("/usr/local/google/home/sbc/dev/wasm/simple{{[/\\]}}test.c")
+; CHECK-NEXT:                DW_AT_decl_line  (5)
+; CHECK-NEXT:                DW_AT_location (DW_OP_addr 0x8)
+
+; CHECK: 0x00000054:   DW_TAG_pointer_type
+; CHECK-NEXT:                DW_AT_type (0x00000059 "void()")
+
+; CHECK: 0x00000059:   DW_TAG_subroutine_type
+; CHECK-NEXT:                DW_AT_prototyped (true)
+
+; CHECK: 0x0000005a:   DW_TAG_subprogram
+; CHECK-NEXT:                DW_AT_low_pc (0x00000002)
+; CHECK-NEXT:                DW_AT_high_pc  (0x00000004)
+; CHECK-NEXT:                DW_AT_frame_base (DW_OP_WASM_location 0x3 0x0, DW_OP_stack_value)
+; CHECK-NEXT:                DW_AT_name ("f2")
+; CHECK-NEXT:                DW_AT_decl_file  ("/usr/local/google/home/sbc/dev/wasm/simple{{[/\\]}}test.c")
+; CHECK-NEXT:                DW_AT_decl_line  (2)
+; CHECK-NEXT:                DW_AT_prototyped (true)
+; CHECK-NEXT:                DW_AT_external   (true)
+
+; CHECK: 0x00000071:   NULL
+
+target triple = "wasm64-unknown-unknown"
+
+source_filename = "test.c"
+
+@myextern = external global i32, align 4
+@foo = hidden global i32* @myextern, align 4, !dbg !0
+@ptr2 = hidden global void ()* @f2, align 4, !dbg !6
+
+; Function Attrs: noinline nounwind optnone
+define hidden void @f2() #0 !dbg !17 {
+entry:
+  ret void, !dbg !18
+}
+
+attributes #0 = { noinline nounwind optnone "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "frame-pointer"="none" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="generic" "unsafe-fp-math"="false" "use-soft-float"="false" }
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!13, !14, !15}
+!llvm.ident = !{!16}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "foo", scope: !2, file: !3, line: 4, type: !11, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 6.0.0 (trunk 315924) (llvm/trunk 315960)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5)
+!3 = !DIFile(filename: "test.c", directory: "/usr/local/google/home/sbc/dev/wasm/simple")
+!4 = !{}
+!5 = !{!0, !6}
+!6 = !DIGlobalVariableExpression(var: !7, expr: !DIExpression())
+!7 = distinct !DIGlobalVariable(name: "ptr2", scope: !2, file: !3, line: 5, type: !8, isLocal: false, isDefinition: true)
+!8 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !9, size: 64)
+!9 = !DISubroutineType(types: !10)
+!10 = !{null}
+!11 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !12, size: 64)
+!12 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!13 = !{i32 2, !"Dwarf Version", i32 4}
+!14 = !{i32 2, !"Debug Info Version", i32 3}
+!15 = !{i32 1, !"wchar_size", i32 4}
+!16 = !{!"clang version 6.0.0 (trunk 315924) (llvm/trunk 315960)"}
+!17 = distinct !DISubprogram(name: "f2", scope: !3, file: !3, line: 2, type: !9, isLocal: false, isDefinition: true, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: false, unit: !2, retainedNodes: !4)
+!18 = !DILocation(line: 2, column: 16, scope: !17)