[lld] r292146 - Give priority to linker scripts over preemption.

[Hans Wennborg via llvm-commits]

Sounds good to me (let me know if you want me to do it).

Cheers,
Hans

On Mon, Jan 16, 2017 at 10:45 AM, Rafael Avila de Espindola
<rafael.espindola at gmail.com> wrote:
> We would probably pull this to the 4.0 release.
>
> Rafael Espindola via llvm-commits <llvm-commits at lists.llvm.org> writes:
>
>> Author: rafael
>> Date: Mon Jan 16 11:35:23 2017
>> New Revision: 292146
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=292146&view=rev
>> Log:
>> Give priority to linker scripts over preemption.
>>
>> LLD exports symbols that are also present in used shared libraries to
>> make sure they are preempted at runtime. That is a reasonable default,
>> but we must allow for it to be overwritten with linker script. If we
>> don't, libraries that expect to be able to hide a c++ delete operator
>> will fail.
>>
>> This should fix the firebird build.
>>
>> Added:
>>     lld/trunk/test/ELF/version-script-hide-so-symbol.s
>> Modified:
>>     lld/trunk/ELF/SymbolTable.cpp
>>     lld/trunk/ELF/Symbols.cpp
>>     lld/trunk/test/ELF/gc-sections-shared.s
>>
>> Modified: lld/trunk/ELF/SymbolTable.cpp
>> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/SymbolTable.cpp?rev=292146&r1=292145&r2=292146&view=diff
>> ==============================================================================
>> --- lld/trunk/ELF/SymbolTable.cpp (original)
>> +++ lld/trunk/ELF/SymbolTable.cpp Mon Jan 16 11:35:23 2017
>> @@ -426,12 +426,8 @@ void SymbolTable<ELFT>::addShared(Shared
>>    std::tie(S, WasInserted) =
>>        insert(Name, Sym.getType(), STV_DEFAULT, /*CanOmitFromDynSym*/ true, F);
>>    // Make sure we preempt DSO symbols with default visibility.
>> -  if (Sym.getVisibility() == STV_DEFAULT) {
>> +  if (Sym.getVisibility() == STV_DEFAULT)
>>      S->ExportDynamic = true;
>> -    // Exporting preempting symbols takes precedence over linker scripts.
>> -    if (S->VersionId == VER_NDX_LOCAL)
>> -      S->VersionId = VER_NDX_GLOBAL;
>> -  }
>>    if (WasInserted || isa<Undefined<ELFT>>(S->body())) {
>>      replaceBody<SharedSymbol<ELFT>>(S, F, Name, Sym, Verdef);
>>      if (!S->isWeak())
>>
>> Modified: lld/trunk/ELF/Symbols.cpp
>> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Symbols.cpp?rev=292146&r1=292145&r2=292146&view=diff
>> ==============================================================================
>> --- lld/trunk/ELF/Symbols.cpp (original)
>> +++ lld/trunk/ELF/Symbols.cpp Mon Jan 16 11:35:23 2017
>> @@ -299,7 +299,8 @@ uint8_t Symbol::computeBinding() const {
>>      return Binding;
>>    if (Visibility != STV_DEFAULT && Visibility != STV_PROTECTED)
>>      return STB_LOCAL;
>> -  if (VersionId == VER_NDX_LOCAL && !body()->isUndefined())
>> +  const SymbolBody *Body = body();
>> +  if (VersionId == VER_NDX_LOCAL && !Body->isUndefined() && !Body->isShared())
>>      return STB_LOCAL;
>>    if (Config->NoGnuUnique && Binding == STB_GNU_UNIQUE)
>>      return STB_GLOBAL;
>>
>> Modified: lld/trunk/test/ELF/gc-sections-shared.s
>> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/gc-sections-shared.s?rev=292146&r1=292145&r2=292146&view=diff
>> ==============================================================================
>> --- lld/trunk/test/ELF/gc-sections-shared.s (original)
>> +++ lld/trunk/test/ELF/gc-sections-shared.s Mon Jan 16 11:35:23 2017
>> @@ -19,15 +19,6 @@
>>  # CHECK-NEXT:     Section: Undefined (0x0)
>>  # CHECK-NEXT:   }
>>  # CHECK-NEXT:   Symbol {
>> -# CHECK-NEXT:     Name: bar
>> -# CHECK-NEXT:     Value:
>> -# CHECK-NEXT:     Size:
>> -# CHECK-NEXT:     Binding: Global
>> -# CHECK-NEXT:     Type:
>> -# CHECK-NEXT:     Other:
>> -# CHECK-NEXT:     Section: .text
>> -# CHECK-NEXT:   }
>> -# CHECK-NEXT:   Symbol {
>>  # CHECK-NEXT:     Name: bar2
>>  # CHECK-NEXT:     Value:
>>  # CHECK-NEXT:     Size:
>>
>> Added: lld/trunk/test/ELF/version-script-hide-so-symbol.s
>> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/version-script-hide-so-symbol.s?rev=292146&view=auto
>> ==============================================================================
>> --- lld/trunk/test/ELF/version-script-hide-so-symbol.s (added)
>> +++ lld/trunk/test/ELF/version-script-hide-so-symbol.s Mon Jan 16 11:35:23 2017
>> @@ -0,0 +1,28 @@
>> +# REQUIRES: x86
>> +
>> +# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
>> +# RUN: ld.lld -shared %t.o -o %t2.so
>> +# RUN: echo "{ local: *; };" > %t.script
>> +# RUN: ld.lld --version-script %t.script -shared %t.o %t2.so -o %t.so
>> +# RUN: llvm-readobj -dyn-symbols %t.so | FileCheck %s
>> +
>> +# The symbol foo must be hidden. This matches bfd and gold and is
>> +# required to make it possible for a c++ library to hide its own
>> +# operator delete.
>> +
>> +# CHECK:      DynamicSymbols [
>> +# CHECK-NEXT:   Symbol {
>> +# CHECK-NEXT:     Name: @ (0)
>> +# CHECK-NEXT:     Value: 0x0
>> +# CHECK-NEXT:     Size: 0
>> +# CHECK-NEXT:     Binding: Local
>> +# CHECK-NEXT:     Type: None
>> +# CHECK-NEXT:     Other: 0
>> +# CHECK-NEXT:     Section: Undefined
>> +# CHECK-NEXT:   }
>> +# CHECK-NEXT: ]
>> +
>> +        .global foo
>> +foo:
>> +     nop
>> +
>>
>>
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