[PATCH] D126257: Round up zero-sized symbols to 1 byte in `.debug_aranges`.

[Patrick Walton via Phabricator via llvm-commits]

pcwalton updated this revision to Diff 431834.
pcwalton added a comment.

Emit a constant 1 instead of a more complicated MCExpr when emitting symbols of length 1.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D126257/new/

https://reviews.llvm.org/D126257

Files:
  llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
  llvm/test/CodeGen/Generic/dwarf-aranges-zero-size.ll
  llvm/test/DebugInfo/MSP430/dwarf-basics-v5.ll
  llvm/test/DebugInfo/X86/dwarf-aranges.ll


Index: llvm/test/DebugInfo/X86/dwarf-aranges.ll
===================================================================
--- llvm/test/DebugInfo/X86/dwarf-aranges.ll
+++ llvm/test/DebugInfo/X86/dwarf-aranges.ll
@@ -22,7 +22,7 @@
 
 ; <text section> - it should have made one span covering all functions in this CU.
 ; CHECK-NEXT: .quad .Lfunc_begin0
-; CHECK-NEXT: .quad .Lsec_end2-.Lfunc_begin0
+; CHECK-NEXT: .quad 1
 
 ; -- finish --
 ; CHECK-NEXT: # ARange terminator
Index: llvm/test/DebugInfo/MSP430/dwarf-basics-v5.ll
===================================================================
--- llvm/test/DebugInfo/MSP430/dwarf-basics-v5.ll
+++ llvm/test/DebugInfo/MSP430/dwarf-basics-v5.ll
@@ -98,7 +98,7 @@
 
 ; CHECK:      .debug_aranges contents:
 ; CHECK-NEXT: Address Range Header: length = 0x{{.*}}, format = DWARF32, version = 0x0002, cu_offset = 0x00000000, addr_size = 0x02, seg_size = 0x00
-; CHECK-NEXT: [0x0000, 0x0006)
+; CHECK-NEXT: [0x0000, 0x0001)
 
 ; CHECK:      .debug_addr contents:
 ; CHECK-NEXT: Address table header: length = 0x{{.*}}, format = DWARF32, version = 0x0005, addr_size = 0x02, seg_size = 0x00
Index: llvm/test/CodeGen/Generic/dwarf-aranges-zero-size.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/Generic/dwarf-aranges-zero-size.ll
@@ -0,0 +1,23 @@
+; Ensures that the AsmPrinter doesn't emit zero-sized symbols into `.debug_aranges`.
+;
+; RUN: llc --generate-arange-section < %s | FileCheck %s
+; CHECK: .section .debug_aranges
+; CHECK: .quad EXAMPLE
+; CHECK-NEXT: .quad 1
+; CHECK: .section
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+ at EXAMPLE = constant <{ [0 x i8] }> zeroinitializer, align 1, !dbg !0
+
+!llvm.module.flags = !{!3}
+!llvm.dbg.cu = !{!4}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "EXAMPLE", linkageName: "EXAMPLE", scope: null, file: null, line: 161, type: !2, isLocal: false, isDefinition: true, align: 1)
+!2 = !DIBasicType(name: "()", encoding: DW_ATE_unsigned)
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = distinct !DICompileUnit(language: DW_LANG_Rust, file: !5, producer: "rustc", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: null, globals: !6)
+!5 = !DIFile(filename: "foo", directory: "")
+!6 = !{!0}
Index: llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
===================================================================
--- llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -3042,13 +3042,17 @@
     for (const ArangeSpan &Span : List) {
       Asm->emitLabelReference(Span.Start, PtrSize);
 
-      // Calculate the size as being from the span start to it's end.
-      if (Span.End) {
+      // Calculate the size as being from the span start to its end.
+      //
+      // If the size is zero, then round it up to one byte. The DWARF
+      // specification requires that entries in this table have nonzero
+      // lengths.
+      uint64_t Size = SymSize[Span.Start];
+      if (Size != 0 && Span.End) {
         Asm->emitLabelDifference(Span.End, Span.Start, PtrSize);
       } else {
         // For symbols without an end marker (e.g. common), we
         // write a single arange entry containing just that one symbol.
-        uint64_t Size = SymSize[Span.Start];
         if (Size == 0)
           Size = 1;
 


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