[WebAssembly] Fix split-dwarf not emitting DW_OP_WASM_location correctly

[aardappel]

Summary

It was using the regular path for target indices that uses uleb, but TI_GLOBAL_RELOC needs to be uint32_t.
Introduced here: https://reviews.llvm.org/D85685
Fixes: https://github.com/emscripten-core/emscripten/issues/13240

[dschuff]

Would it make sense to also run e.g. llvm/test/MC/WebAssembly/debug-localvar.ll with split-dwarf?

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

475

Can we assert that the index is 0?

[aardappel]

Added test

[aardappel]

Would it make sense to also run e.g. llvm/test/MC/WebAssembly/debug-localvar.ll with split-dwarf?

That file doesn't contain a use of TI_GLOBAL_RELOC, so I instead added to dwarfdump.ll. Sadly the split dwarf output is sufficiently different in many places that my attempt to interleave it with the regular output became too unreadable, so it is now a side-by-side output.

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

475

Yup that is already done a little up from this code:

assert(FrameBase.Location.WasmLoc.Index == 0); // Only SP so far.

[dschuff]

otherwise LGTM

[dschuff]

llvm/test/MC/WebAssembly/dwarfdump.ll

68

wait, did my comment get eaten by Phabricator?

This path check will presumably fail on non-windows. I guess it's because %s gets expanded to an absolute path by lit. I guess we could just check for a regex that only matches DW_AT_GNU_dwo_name, and the filename?

[aardappel]

Fixed windows path & test leaving non-temp files behind.

[aardappel]

llvm/test/MC/WebAssembly/dwarfdump.ll

68

Thanks, nice catch.. would have definitely broken the build.

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

case TargetFrameLowering::DwarfFrameBase::CFA: {
       addUInt(*Loc, dwarf::DW_FORM_data1, dwarf::DW_OP_call_frame_cfa);
       addBlock(*SPDie, dwarf::DW_AT_frame_base, Loc);
       break;
     }
     case TargetFrameLowering::DwarfFrameBase::WasmFrameBase: {
       // FIXME: duplicated from Target/WebAssembly/WebAssembly.h
       // don't want to depend on target specific headers in this code?
       const unsigned TI_GLOBAL_RELOC = 3;
-      // FIXME: when writing dwo, we need to avoid relocations. Probably
-      // the "right" solution is to treat globals the way func and data symbols
-      // are (with entries in .debug_addr).
-      if (FrameBase.Location.WasmLoc.Kind == TI_GLOBAL_RELOC && !isDwoUnit()) {
+      if (FrameBase.Location.WasmLoc.Kind == TI_GLOBAL_RELOC) {
         // These need to be relocatable.
         assert(FrameBase.Location.WasmLoc.Index == 0);  // Only SP so far.
         auto SPSym = cast<MCSymbolWasm>(
           Asm->GetExternalSymbolSymbol("__stack_pointer"));
         // FIXME: this repeats what WebAssemblyMCInstLower::
         // GetExternalSymbolSymbol does, since if there's no code that
         // refers to this symbol, we have to set it here.
         SPSym->setType(wasm::WASM_SYMBOL_TYPE_GLOBAL);
         SPSym->setGlobalType(wasm::WasmGlobalType{
             uint8_t(Asm->getSubtargetInfo().getTargetTriple().getArch() ==
                             Triple::wasm64
                         ? wasm::WASM_TYPE_I64
                         : wasm::WASM_TYPE_I32),
             true});
         DIELoc *Loc = new (DIEValueAllocator) DIELoc;
         addUInt(*Loc, dwarf::DW_FORM_data1, dwarf::DW_OP_WASM_location);
         addSInt(*Loc, dwarf::DW_FORM_sdata, TI_GLOBAL_RELOC);
+        if (!isDwoUnit()) {
           addLabel(*Loc, dwarf::DW_FORM_data4, SPSym);
           DD->addArangeLabel(SymbolCU(this, SPSym));
+        } else {
+          // FIXME: when writing dwo, we need to avoid relocations. Probably
+          // the "right" solution is to treat globals the way func and data
+          // symbols are (with entries in .debug_addr).
+          // For now, since we only ever use index 0, this should work as-is.       
+          addUInt(*Loc, dwarf::DW_FORM_data4, FrameBase.Location.WasmLoc.Index);
+        }
         addUInt(*Loc, dwarf::DW_FORM_data1, dwarf::DW_OP_stack_value);
         addBlock(*SPDie, dwarf::DW_AT_frame_base, Loc);
       } else {
         DIELoc *Loc = new (DIEValueAllocator) DIELoc;
         DIEDwarfExpression DwarfExpr(*Asm, *this, *Loc);
         DIExpressionCursor Cursor({});
         DwarfExpr.addWasmLocation(FrameBase.Location.WasmLoc.Kind,
             FrameBase.Location.WasmLoc.Index);

llvm/test/MC/WebAssembly/dwarfdump.ll

 ; RUN: llc -filetype=obj %s -o - | llvm-dwarfdump - | FileCheck %s
+; RUN: llc -filetype=obj --split-dwarf-file=%t.dwo --split-dwarf-output=%t.dwo %s -o %t.o
+; RUN: llvm-dwarfdump %t.dwo | FileCheck %s -check-prefix=SPLIT
 
 ; 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_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
 
+
+; SPLIT:      .debug_info.dwo contents:
+; SPLIT-NEXT: 0x00000000: Compile Unit: length = 0x0000004c, format = DWARF32, version = 0x0004, abbr_offset = 0x0000, addr_size = 0x04 (next unit at 0x00000050)
+
+; SPLIT:      0x0000000b: DW_TAG_compile_unit
+; SPLIT-NEXT:               DW_AT_producer    ("clang version 6.0.0 (trunk 315924) (llvm/trunk 315960)")
+; SPLIT-NEXT:               DW_AT_language    (DW_LANG_C99)
+; SPLIT-NEXT:               DW_AT_name        ("test.c")
+; SPLIT-NEXT:               DW_AT_GNU_dwo_name        ("{{.*}}dwarfdump.ll.tmp.dwo")
+; SPLIT-NEXT:               DW_AT_GNU_dwo_id  (0xad3151f12153fa17)
+
+; SPLIT:      0x00000019:   DW_TAG_variable
+; SPLIT-NEXT:                 DW_AT_name      ("foo")
+; SPLIT-NEXT:                 DW_AT_type      (0x00000024 "int*")
+; SPLIT-NEXT:                 DW_AT_external  (true)
+; SPLIT-NEXT:                 DW_AT_decl_file (0x01)
+; SPLIT-NEXT:                 DW_AT_decl_line (4)
+; SPLIT-NEXT:                 DW_AT_location  (DW_OP_GNU_addr_index 0x0)
+
+; SPLIT:      0x00000024:   DW_TAG_pointer_type
+; SPLIT-NEXT:                 DW_AT_type      (0x00000029 "int")
+
+; SPLIT:      0x00000029:   DW_TAG_base_type
+; SPLIT-NEXT:                 DW_AT_name      ("int")
+; SPLIT-NEXT:                 DW_AT_encoding  (DW_ATE_signed)
+; SPLIT-NEXT:                 DW_AT_byte_size (0x04)
+
+; SPLIT:      0x0000002d:   DW_TAG_variable
+; SPLIT-NEXT:                 DW_AT_name      ("ptr2")
+; SPLIT-NEXT:                 DW_AT_type      (0x00000038 "void()*")
+; SPLIT-NEXT:                 DW_AT_external  (true)
+; SPLIT-NEXT:                 DW_AT_decl_file (0x01)
+; SPLIT-NEXT:                 DW_AT_decl_line (5)
+; SPLIT-NEXT:                 DW_AT_location  (DW_OP_GNU_addr_index 0x1)
+
+; SPLIT:      0x00000038:   DW_TAG_pointer_type
+; SPLIT-NEXT:                 DW_AT_type      (0x0000003d "void()")
+
+; SPLIT:      0x0000003d:   DW_TAG_subroutine_type
+; SPLIT-NEXT:                 DW_AT_prototyped        (true)
+
+; SPLIT:      0x0000003e:   DW_TAG_subprogram
+; SPLIT-NEXT:                 DW_AT_low_pc    (indexed (00000002) address = <unresolved>)
+; SPLIT-NEXT:                 DW_AT_high_pc   (0x00000002)
+; SPLIT-NEXT:                 DW_AT_frame_base        (DW_OP_WASM_location 0x3 0x0, DW_OP_stack_value)
+; SPLIT-NEXT:                 DW_AT_name      ("f2")
+; SPLIT-NEXT:                 DW_AT_decl_file (0x01)
+; SPLIT-NEXT:                 DW_AT_decl_line (2)
+; SPLIT-NEXT:                 DW_AT_prototyped        (true)
+; SPLIT-NEXT:                 DW_AT_external  (true)
+
+; SPLIT:      0x0000004f:   NULL
+
+
 target triple = "wasm32-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