[llvm-commits] [lld] r172553 - in /lld/trunk: lib/ReaderWriter/ELF/ReaderELF.cpp test/elf/check.objtxt

[Michael Spencer]

On Tue, Jan 15, 2013 at 3:42 PM, Nick Kledzik <kledzik at apple.com> wrote:
> But you do want content for weak symbols that are C++ out-of-line copies.
> I thought it was just weak aliases that needed this (or at least the use of
> weak aliases in the runtime sample you had).
>
> -Nick

Unless a weak symbol is the only symbol in a section, there is no way
to know that it should own the content. .gnu.linkonce solves this for
some cases.

- Michael Spencer

>
> On Jan 15, 2013, at 1:13 PM, Michael J. Spencer wrote:
>> Author: mspencer
>> Date: Tue Jan 15 15:13:02 2013
>> New Revision: 172553
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=172553&view=rev
>> Log:
>> [ELF] Never allocate content to weak symbols as they may be merged away.
>>
>> This is done by creating a new non-weak anonymous symbol and creating
>> an atom with content for that symbol. This is added after the weak symbol
>> so that they have the same address.
>>
>> Modified:
>>    lld/trunk/lib/ReaderWriter/ELF/ReaderELF.cpp
>>    lld/trunk/test/elf/check.objtxt
>>
>> Modified: lld/trunk/lib/ReaderWriter/ELF/ReaderELF.cpp
>> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/lib/ReaderWriter/ELF/ReaderELF.cpp?rev=172553&r1=172552&r2=172553&view=diff
>> ==============================================================================
>> --- lld/trunk/lib/ReaderWriter/ELF/ReaderELF.cpp (original)
>> +++ lld/trunk/lib/ReaderWriter/ELF/ReaderELF.cpp Tue Jan 15 15:13:02 2013
>> @@ -215,6 +215,22 @@
>>                                    : (*(si + 1))->st_value - (*si)->st_value;
>>         }
>>
>> +
>> +        // Don't allocate content to a weak symbol, as they may be merged away.
>> +        // Create an anonymous atom to hold the data.
>> +        ELFDefinedAtom<ELFT> *anonAtom = nullptr;
>> +        if ((*si)->getBinding() == llvm::ELF::STB_WEAK && contentSize != 0) {
>> +          // Create a new non-weak ELF symbol.
>> +          auto sym = new (_readerStorage.Allocate<Elf_Sym>()) Elf_Sym;
>> +          *sym = **si;
>> +          sym->setBinding(llvm::ELF::STB_GLOBAL);
>> +          anonAtom = createDefinedAtomAndAssignRelocations(
>> +            "", sectionName, sym, i.first,
>> +            ArrayRef<uint8_t>(
>> +              (uint8_t *)sectionContents.data() + (*si)->st_value, contentSize));
>> +          contentSize = 0;
>> +        }
>> +
>>         ArrayRef<uint8_t> symbolData = ArrayRef<uint8_t>(
>>           (uint8_t *)sectionContents.data() + (*si)->st_value, contentSize);
>>
>> @@ -223,6 +239,8 @@
>>
>>         _definedAtoms._atoms.push_back(newAtom);
>>         _symbolToAtomMapping.insert(std::make_pair((*si), newAtom));
>> +        if (anonAtom)
>> +          _definedAtoms._atoms.push_back(anonAtom);
>>       }
>>     }
>>
>>
>> Modified: lld/trunk/test/elf/check.objtxt
>> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/elf/check.objtxt?rev=172553&r1=172552&r2=172553&view=diff
>> ==============================================================================
>> --- lld/trunk/test/elf/check.objtxt (original)
>> +++ lld/trunk/test/elf/check.objtxt Tue Jan 15 15:13:02 2013
>> @@ -13,9 +13,9 @@
>>
>> ELF-i386:    - name:              weak_func
>> ELF-i386:      scope:             global
>> -ELF-i386:      content:           [ 55, 89, E5, 83, EC, 18, C7, 04, 24, 0E, 00, 00,
>> -ELF-i386:                           00, E8, FC, FF, FF, FF, C9, C3 ]
>> ELF-i386:      merge:             as-weak
>> +ELF-i386:      content:           [ 55, 89, E5, 83, EC, 18, C7, 04, 24, 0E, 00, 00,
>> +ELF-i386:                           00, E8, FC, FF, FF, FF, C9, C3 ]
>>
>> ELF-i386:    - name:              hidden_func
>> ELF-i386:      scope:             hidden
>> @@ -65,9 +65,9 @@
>>
>> ELF-hexagon:    - name:              weak_func
>> ELF-hexagon:      scope:             global
>> -ELF-hexagon:      content:           [ 00, C0, 9D, A0, 00, 40, 00, 00, 00, C0, 00, 78,
>> -ELF-hexagon:                           00, C0, 00, 5A, 1E, C0, 1E, 96 ]
>> ELF-hexagon:      merge:             as-weak
>> +ELF-hexagon:      content:           [ 00, C0, 9D, A0, 00, 40, 00, 00, 00, C0, 00, 78,
>> +ELF-hexagon:                           00, C0, 00, 5A, 1E, C0, 1E, 96 ]
>>
>> ELF-hexagon:    - name:              hidden_func
>> ELF-hexagon:      scope:             hidden
>>
>>
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