[PATCH] Remove wild .debug_aranges entries generated from unimportant labels

[Alexey Samsonov]

Sure, here you go:

$ cat tmp/debug_ranges/a.cc
int global = 2;
int foo(int bar) { return bar; }
int foo2(int bar2) { return bar2; }

int main() {
  return foo(2) + foo2(1) + global;
}
$ ./bin/clang++ -g -O1 tmp/debug_ranges/a.cc
$ readelf -wr a.out
Contents of the .debug_aranges section:

  Length:                   92
  Version:                  2
  Offset into .debug_info:  0x0
  Pointer Size:             8
  Segment Size:             0

    Address            Length
    0000000000000000 0000000000000001 <----- huh?
    0000000000000036 0000000000000001 <----- hm?
    0000000000402018 0000000000000004
    0000000000400510 0000000000000041
    0000000000000000 0000000000000000


On Wed, Oct 2, 2013 at 10:23 PM, Richard Mitton <richard at codersnotes.com>wrote:

> How would I go about reproducing this bug? I'd really like to see a test
> case.
>
> Richard Mitton
> richard at codersnotes.com
>
>
> On 10/02/2013 07:10 AM, Alexey Samsonov wrote:
>
>> Hi echristo,
>>
>> r191052 added emitting .debug_aranges to Clang, but this
>> functionality is broken: it uses all MC labels added in DWARF Asm
>> printer, including the labels for build relocations between
>> different DWARF sections, like .Lsection_line or .Ldebug_loc0.
>>
>> As a result, if any DIE .debug_info would contain "DW_AT_location=0x123"
>> attribute, .debug_aranges would also contain a range starting from 0x123,
>> breaking tools that rely on this section.
>>
>> I'm not sure this is the correct fix, please take a look.
>>
>> http://llvm-reviews.chandlerc.**com/D1809<http://llvm-reviews.chandlerc.com/D1809>
>>
>> Files:
>>    lib/CodeGen/AsmPrinter/**DwarfDebug.cpp
>>    lib/CodeGen/AsmPrinter/**DwarfCompileUnit.cpp
>>    lib/CodeGen/AsmPrinter/**DwarfDebug.h
>>
>> Index: lib/CodeGen/AsmPrinter/**DwarfDebug.cpp
>> ==============================**==============================**=======
>> --- lib/CodeGen/AsmPrinter/**DwarfDebug.cpp
>> +++ lib/CodeGen/AsmPrinter/**DwarfDebug.cpp
>> @@ -1110,8 +1110,8 @@
>>     void DwarfDebug::endSections() {
>>      // Filter labels by section.
>> -  for (size_t n = 0; n < Labels.size(); n++) {
>> -    const SymbolCU &SCU = Labels[n];
>> +  for (size_t n = 0; n < ArangeLabels.size(); n++) {
>> +    const SymbolCU &SCU = ArangeLabels[n];
>>       if (SCU.Sym->isInSection()) {
>>         // Make a note of this symbol and it's section.
>>         const MCSection *Section = &SCU.Sym->getSection();
>> @@ -1138,10 +1138,7 @@
>>       }
>>         // Insert a final terminator.
>> -    SymbolCU Entry;
>> -    Entry.CU = NULL;
>> -    Entry.Sym = Sym;
>> -    SectionMap[Section].push_back(**Entry);
>> +    SectionMap[Section].push_back(**SymbolCU(NULL, Sym));
>>     }
>>   }
>>   Index: lib/CodeGen/AsmPrinter/**DwarfCompileUnit.cpp
>> ==============================**==============================**=======
>> --- lib/CodeGen/AsmPrinter/**DwarfCompileUnit.cpp
>> +++ lib/CodeGen/AsmPrinter/**DwarfCompileUnit.cpp
>> @@ -181,26 +181,15 @@
>>                              const MCSymbol *Label) {
>>     DIEValue *Value = new (DIEValueAllocator) DIELabel(Label);
>>     Die->addValue(Attribute, Form, Value);
>> -
>> -  SymbolCU Entry;
>> -  Entry.CU = this;
>> -  Entry.Sym = Label;
>> -
>> -  DD->addLabel(Entry);
>>   }
>>     /// addLabelAddress - Add a dwarf label attribute data and value using
>>   /// DW_FORM_addr or DW_FORM_GNU_addr_index.
>>   ///
>>   void CompileUnit::addLabelAddress(**DIE *Die, uint16_t Attribute,
>>                                     MCSymbol *Label) {
>> -  if (Label) {
>> -    SymbolCU Entry;
>> -    Entry.CU = this;
>> -    Entry.Sym = Label;
>> -
>> -    DD->addLabel(Entry);
>> -  }
>> +  if (Label)
>> +    DD->addArangeLabel(SymbolCU(**this, Label));
>>       if (!DD->useSplitDwarf()) {
>>       if (Label != NULL) {
>> @@ -221,6 +210,7 @@
>>   /// form given and an op of either DW_FORM_addr or
>> DW_FORM_GNU_addr_index.
>>   ///
>>   void CompileUnit::addOpAddress(DIE *Die, const MCSymbol *Sym) {
>> +  DD->addArangeLabel(SymbolCU(**this, Sym));
>>     if (!DD->useSplitDwarf()) {
>>       addUInt(Die, 0, dwarf::DW_FORM_data1, dwarf::DW_OP_addr);
>>       addLabel(Die, 0, dwarf::DW_FORM_udata, Sym);
>> Index: lib/CodeGen/AsmPrinter/**DwarfDebug.h
>> ==============================**==============================**=======
>> --- lib/CodeGen/AsmPrinter/**DwarfDebug.h
>> +++ lib/CodeGen/AsmPrinter/**DwarfDebug.h
>> @@ -303,6 +303,7 @@
>>     /// \brief Helper used to pair up a symbol and it's DWARF compile
>> unit.
>>   struct SymbolCU {
>> +  SymbolCU(CompileUnit *CU, const MCSymbol *Sym) : Sym(Sym), CU(CU) {}
>>     const MCSymbol *Sym;
>>     CompileUnit *CU;
>>   };
>> @@ -363,8 +364,8 @@
>>     // separated by a zero byte, mapped to a unique id.
>>     StringMap<unsigned, BumpPtrAllocator&> SourceIdMap;
>>   -  // List of all labels used in the output.
>> -  std::vector<SymbolCU> Labels;
>> +  // List of all labels used in aranges generation.
>> +  std::vector<SymbolCU> ArangeLabels;
>>       // Size of each symbol emitted (for those symbols that have a
>> specific size).
>>     DenseMap <const MCSymbol *, uint64_t> SymSize;
>> @@ -731,7 +732,7 @@
>>     void addTypeUnitType(DIE *Die) { TypeUnits.push_back(Die); }
>>       /// \brief Add a label so that arange data can be generated for it.
>> -  void addLabel(SymbolCU SCU) { Labels.push_back(SCU); }
>> +  void addArangeLabel(SymbolCU SCU) { ArangeLabels.push_back(SCU); }
>>       /// \brief For symbols that have a size designated (e.g. common
>> symbols),
>>     /// this tracks that size.
>>
>
>


-- 
Alexey Samsonov, MSK
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