[PATCH] D126835: Round up zero-sized symbols to 1 byte in `.debug_aranges` (without breaking other logic).

[Patrick Walton via Phabricator via llvm-commits]

pcwalton updated this revision to Diff 435277.
pcwalton added a comment.
Herald added a subscriber: ormris.

Updated the diff to address comments.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D126835/new/

https://reviews.llvm.org/D126835

Files:
  llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
  llvm/test/CodeGen/X86/dwarf-aranges-zero-size.ll


Index: llvm/test/CodeGen/X86/dwarf-aranges-zero-size.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/X86/dwarf-aranges-zero-size.ll
@@ -0,0 +1,39 @@
+; Ensures that the AsmPrinter rounds up zero-sized symbols in `.debug_aranges` to one byte.
+
+; Generated from the following Rust source:
+; 
+;     pub static EXAMPLE: () = ();
+;
+; Compiled with:
+;
+;     $ rustc --crate-type=lib --target=x86_64-unknown-linux-gnu --emit=llvm-ir -g dwarf-aranges-zero-size.rs
+
+; RUN: llc --generate-arange-section < %s | FileCheck %s
+; CHECK: .section .debug_aranges
+; CHECK: .quad _ZN23dwarf_aranges_zero_size7EXAMPLE17h8ab19f2b0c3b238dE
+; CHECK-NEXT: .quad 1
+; CHECK: .section
+
+; ModuleID = 'dwarf_aranges_zero_size.fbc28187-cgu.0'
+source_filename = "dwarf_aranges_zero_size.fbc28187-cgu.0"
+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 _ZN23dwarf_aranges_zero_size7EXAMPLE17h8ab19f2b0c3b238dE = constant <{ [0 x i8] }> zeroinitializer, align 1, !dbg !0
+ at __rustc_debug_gdb_scripts_section__ = linkonce_odr unnamed_addr constant [34 x i8] c"\01gdb_load_rust_pretty_printers.py\00", section ".debug_gdb_scripts", align 1
+
+!llvm.module.flags = !{!5, !6, !7}
+!llvm.dbg.cu = !{!8}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "EXAMPLE", linkageName: "_ZN23dwarf_aranges_zero_size7EXAMPLE17h8ab19f2b0c3b238dE", scope: !2, file: !3, line: 1, type: !4, isLocal: false, isDefinition: true, align: 8)
+!2 = !DINamespace(name: "dwarf_aranges_zero_size", scope: null)
+!3 = !DIFile(filename: "dwarf-aranges-zero-size.rs", directory: "/Users/pcwalton/Desktop", checksumkind: CSK_MD5, checksum: "c2d51547bfaf5562b9c9061311fe4140")
+!4 = !DIBasicType(name: "()", encoding: DW_ATE_unsigned)
+!5 = !{i32 7, !"PIC Level", i32 2}
+!6 = !{i32 2, !"RtLibUseGOT", i32 1}
+!7 = !{i32 2, !"Debug Info Version", i32 3}
+!8 = distinct !DICompileUnit(language: DW_LANG_Rust, file: !9, producer: "clang LLVM (rustc version 1.60.0-nightly (0c292c966 2022-02-08))", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !10, globals: !11)
+!9 = !DIFile(filename: "dwarf-aranges-zero-size.rs/@/dwarf_aranges_zero_size.fbc28187-cgu.0", directory: "/Users/pcwalton/Desktop")
+!10 = !{}
+!11 = !{!0}
Index: llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
===================================================================
--- llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -3042,13 +3042,18 @@
     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.
+      auto SizeRef = SymSize.find(Span.Start);
+      if ((SizeRef == SymSize.end() || SizeRef->second != 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];
+        uint64_t Size = SizeRef->second;
         if (Size == 0)
           Size = 1;
 


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