<div dir="ltr">So, we don't want weak undefined symbols to fetch archive members, which sounds fine, but I still doesn't get how is this related to --start-group and --end-group in regular ELF linkers. I'm just wondering... Could you describe a bit?</div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Oct 6, 2015 at 7:33 AM, Rafael Espindola via llvm-commits <span dir="ltr"><<a href="mailto:llvm-commits@lists.llvm.org" target="_blank">llvm-commits@lists.llvm.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Author: rafael<br>
Date: Tue Oct 6 09:33:58 2015<br>
New Revision: 249406<br>
<br>
URL: <a href="http://llvm.org/viewvc/llvm-project?rev=249406&view=rev" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project?rev=249406&view=rev</a><br>
Log:<br>
Handle strong undefined symbols fetching members after a weak undefined.<br>
<br>
This is a case that requires --start-group --end-group with regular ELF<br>
linkers. Fortunately it is still possible to handle it with lazy symbols without<br>
taking a second look at archives.<br>
<br>
Thanks to Michael Spencer for the bug report.<br>
<br>
Added:<br>
lld/trunk/test/elf2/Inputs/archive3.s<br>
lld/trunk/test/elf2/Inputs/archive4.s<br>
Modified:<br>
lld/trunk/ELF/InputSection.cpp<br>
lld/trunk/ELF/OutputSections.cpp<br>
lld/trunk/ELF/OutputSections.h<br>
lld/trunk/ELF/SymbolTable.cpp<br>
lld/trunk/ELF/Symbols.h<br>
lld/trunk/test/elf2/archive.s<br>
<br>
Modified: lld/trunk/ELF/InputSection.cpp<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/InputSection.cpp?rev=249406&r1=249405&r2=249406&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/InputSection.cpp?rev=249406&r1=249405&r2=249406&view=diff</a><br>
==============================================================================<br>
--- lld/trunk/ELF/InputSection.cpp (original)<br>
+++ lld/trunk/ELF/InputSection.cpp Tue Oct 6 09:33:58 2015<br>
@@ -49,8 +49,7 @@ void InputSection<ELFT>::relocate(<br>
continue;<br>
SymVA = getLocalSymVA(Sym, File);<br>
} else {<br>
- const auto &Body =<br>
- *cast<ELFSymbolBody<ELFT>>(File.getSymbolBody(SymIndex));<br>
+ SymbolBody &Body = *File.getSymbolBody(SymIndex);<br>
SymVA = getSymVA<ELFT>(Body, BssSec);<br>
if (Target->relocNeedsPlt(Type, Body)) {<br>
SymVA = PltSec.getEntryAddr(Body);<br>
<br>
Modified: lld/trunk/ELF/OutputSections.cpp<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/OutputSections.cpp?rev=249406&r1=249405&r2=249406&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/OutputSections.cpp?rev=249406&r1=249405&r2=249406&view=diff</a><br>
==============================================================================<br>
--- lld/trunk/ELF/OutputSections.cpp (original)<br>
+++ lld/trunk/ELF/OutputSections.cpp Tue Oct 6 09:33:58 2015<br>
@@ -349,13 +349,14 @@ void OutputSection<ELFT>::addSection(Inp<br>
<br>
template <class ELFT><br>
typename ELFFile<ELFT>::uintX_t<br>
-lld::elf2::getSymVA(const ELFSymbolBody<ELFT> &S,<br>
- const OutputSection<ELFT> &BssSec) {<br>
+lld::elf2::getSymVA(const SymbolBody &S, const OutputSection<ELFT> &BssSec) {<br>
switch (S.kind()) {<br>
- case SymbolBody::DefinedSyntheticKind:<br>
- return cast<DefinedSynthetic<ELFT>>(S).Section.getVA() + S.Sym.st_value;<br>
+ case SymbolBody::DefinedSyntheticKind: {<br>
+ auto &D = cast<DefinedSynthetic<ELFT>>(S);<br>
+ return D.Section.getVA() + D.Sym.st_value;<br>
+ }<br>
case SymbolBody::DefinedAbsoluteKind:<br>
- return S.Sym.st_value;<br>
+ return cast<DefinedAbsolute<ELFT>>(S).Sym.st_value;<br>
case SymbolBody::DefinedRegularKind: {<br>
const auto &DR = cast<DefinedRegular<ELFT>>(S);<br>
const InputSection<ELFT> *SC = &DR.Section;<br>
@@ -368,9 +369,9 @@ lld::elf2::getSymVA(const ELFSymbolBody<<br>
case SymbolBody::UndefinedKind:<br>
return 0;<br>
case SymbolBody::LazyKind:<br>
- break;<br>
+ assert(S.isUsedInRegularObj() && "Lazy symbol reached writer");<br>
+ return 0;<br>
}<br>
- llvm_unreachable("Lazy symbol reached writer");<br>
}<br>
<br>
template <class ELFT><br>
@@ -409,8 +410,6 @@ void StringTableSection<Is64Bits>::write<br>
}<br>
<br>
template <class ELFT> bool lld::elf2::includeInSymtab(const SymbolBody &B) {<br>
- if (B.isLazy())<br>
- return false;<br>
if (!B.isUsedInRegularObj())<br>
return false;<br>
<br>
@@ -521,21 +520,20 @@ void SymbolTableSection<ELFT>::writeGlob<br>
if (StrTabSec.isDynamic() && !includeInDynamicSymtab(*Body))<br>
continue;<br>
<br>
- const auto &EBody = *cast<ELFSymbolBody<ELFT>>(Body);<br>
- const Elf_Sym &InputSym = EBody.Sym;<br>
auto *ESym = reinterpret_cast<Elf_Sym *>(Buf);<br>
Buf += sizeof(*ESym);<br>
+<br>
ESym->st_name = StrTabSec.getFileOff(Name);<br>
<br>
const OutputSection<ELFT> *Out = nullptr;<br>
const InputSection<ELFT> *Section = nullptr;<br>
<br>
- switch (EBody.kind()) {<br>
+ switch (Body->kind()) {<br>
case SymbolBody::DefinedSyntheticKind:<br>
Out = &cast<DefinedSynthetic<ELFT>>(Body)->Section;<br>
break;<br>
case SymbolBody::DefinedRegularKind:<br>
- Section = &cast<DefinedRegular<ELFT>>(EBody).Section;<br>
+ Section = &cast<DefinedRegular<ELFT>>(Body)->Section;<br>
break;<br>
case SymbolBody::DefinedCommonKind:<br>
Out = &BssSec;<br>
@@ -543,25 +541,33 @@ void SymbolTableSection<ELFT>::writeGlob<br>
case SymbolBody::UndefinedKind:<br>
case SymbolBody::DefinedAbsoluteKind:<br>
case SymbolBody::SharedKind:<br>
- break;<br>
case SymbolBody::LazyKind:<br>
- llvm_unreachable("Lazy symbol got to output symbol table!");<br>
+ break;<br>
}<br>
<br>
- unsigned char Binding = InputSym.getBinding();<br>
- unsigned char Visibility = EBody.getMostConstrainingVisibility();<br>
+ unsigned char Binding = Body->isWeak() ? STB_WEAK : STB_GLOBAL;<br>
+ unsigned char Type = STT_NOTYPE;<br>
+ uintX_t Size = 0;<br>
+ if (const auto *EBody = dyn_cast<ELFSymbolBody<ELFT>>(Body)) {<br>
+ const Elf_Sym &InputSym = EBody->Sym;<br>
+ Binding = InputSym.getBinding();<br>
+ Type = InputSym.getType();<br>
+ Size = InputSym.st_size;<br>
+ }<br>
+<br>
+ unsigned char Visibility = Body->getMostConstrainingVisibility();<br>
if (Visibility != STV_DEFAULT && Visibility != STV_PROTECTED)<br>
Binding = STB_LOCAL;<br>
<br>
- ESym->setBindingAndType(Binding, InputSym.getType());<br>
- ESym->st_size = InputSym.st_size;<br>
+ ESym->setBindingAndType(Binding, Type);<br>
+ ESym->st_size = Size;<br>
ESym->setVisibility(Visibility);<br>
- ESym->st_value = getSymVA(EBody, BssSec);<br>
+ ESym->st_value = getSymVA(*Body, BssSec);<br>
<br>
if (Section)<br>
Out = Section->getOutputSection();<br>
<br>
- if (InputSym.isAbsolute())<br>
+ if (isa<DefinedAbsolute<ELFT>>(Body))<br>
ESym->st_shndx = SHN_ABS;<br>
else if (Out)<br>
ESym->st_shndx = Out->getSectionIndex();<br>
@@ -629,17 +635,14 @@ template class SymbolTableSection<ELF32B<br>
template class SymbolTableSection<ELF64LE>;<br>
template class SymbolTableSection<ELF64BE>;<br>
<br>
-template ELFFile<ELF32LE>::uintX_t<br>
-getSymVA(const ELFSymbolBody<ELF32LE> &, const OutputSection<ELF32LE> &);<br>
-<br>
-template ELFFile<ELF32BE>::uintX_t<br>
-getSymVA(const ELFSymbolBody<ELF32BE> &, const OutputSection<ELF32BE> &);<br>
-<br>
-template ELFFile<ELF64LE>::uintX_t<br>
-getSymVA(const ELFSymbolBody<ELF64LE> &, const OutputSection<ELF64LE> &);<br>
-<br>
-template ELFFile<ELF64BE>::uintX_t<br>
-getSymVA(const ELFSymbolBody<ELF64BE> &, const OutputSection<ELF64BE> &);<br>
+template ELFFile<ELF32LE>::uintX_t getSymVA(const SymbolBody &,<br>
+ const OutputSection<ELF32LE> &);<br>
+template ELFFile<ELF32BE>::uintX_t getSymVA(const SymbolBody &,<br>
+ const OutputSection<ELF32BE> &);<br>
+template ELFFile<ELF64LE>::uintX_t getSymVA(const SymbolBody &,<br>
+ const OutputSection<ELF64LE> &);<br>
+template ELFFile<ELF64BE>::uintX_t getSymVA(const SymbolBody &,<br>
+ const OutputSection<ELF64BE> &);<br>
<br>
template ELFFile<ELF32LE>::uintX_t<br>
getLocalSymVA(const ELFFile<ELF32LE>::Elf_Sym *, const ObjectFile<ELF32LE> &);<br>
<br>
Modified: lld/trunk/ELF/OutputSections.h<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/OutputSections.h?rev=249406&r1=249405&r2=249406&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/OutputSections.h?rev=249406&r1=249405&r2=249406&view=diff</a><br>
==============================================================================<br>
--- lld/trunk/ELF/OutputSections.h (original)<br>
+++ lld/trunk/ELF/OutputSections.h Tue Oct 6 09:33:58 2015<br>
@@ -34,7 +34,7 @@ template <class ELFT> class ELFSymbolBod<br>
<br>
template <class ELFT><br>
typename llvm::object::ELFFile<ELFT>::uintX_t<br>
-getSymVA(const ELFSymbolBody<ELFT> &S, const OutputSection<ELFT> &BssSec);<br>
+getSymVA(const SymbolBody &S, const OutputSection<ELFT> &BssSec);<br>
<br>
template <class ELFT><br>
typename llvm::object::ELFFile<ELFT>::uintX_t<br>
<br>
Modified: lld/trunk/ELF/SymbolTable.cpp<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/SymbolTable.cpp?rev=249406&r1=249405&r2=249406&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/SymbolTable.cpp?rev=249406&r1=249405&r2=249406&view=diff</a><br>
==============================================================================<br>
--- lld/trunk/ELF/SymbolTable.cpp (original)<br>
+++ lld/trunk/ELF/SymbolTable.cpp Tue Oct 6 09:33:58 2015<br>
@@ -256,10 +256,23 @@ void SymbolTable::addLazy(Lazy *New) {<br>
if (Sym->Body == New)<br>
return;<br>
SymbolBody *Existing = Sym->Body;<br>
- if (Existing->isDefined() || Existing->isLazy() || Existing->isWeak())<br>
+ if (Existing->isDefined() || Existing->isLazy())<br>
return;<br>
Sym->Body = New;<br>
assert(Existing->isUndefined() && "Unexpected symbol kind.");<br>
+<br>
+ // Weak undefined symbols should not fetch members from archives.<br>
+ // If we were to keep old symbol we would not know that an archive member was<br>
+ // available if a strong undefined symbol shows up afterwards in the link.<br>
+ // If a strong undefined symbol never shows up, this lazy symbol will<br>
+ // get to the end of the link and must be treated as the weak undefined one.<br>
+ // We set UsedInRegularObj in a similar way to what is done with shared<br>
+ // symbols and mark it as weak to reduce how many special cases are needed.<br>
+ if (Existing->isWeak()) {<br>
+ New->setUsedInRegularObj();<br>
+ New->setWeak();<br>
+ return;<br>
+ }<br>
addMemberFile(New);<br>
}<br>
<br>
<br>
Modified: lld/trunk/ELF/Symbols.h<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Symbols.h?rev=249406&r1=249405&r2=249406&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Symbols.h?rev=249406&r1=249405&r2=249406&view=diff</a><br>
==============================================================================<br>
--- lld/trunk/ELF/Symbols.h (original)<br>
+++ lld/trunk/ELF/Symbols.h Tue Oct 6 09:33:58 2015<br>
@@ -103,7 +103,7 @@ protected:<br>
}<br>
<br>
const unsigned SymbolKind : 8;<br>
- const unsigned IsWeak : 1;<br>
+ unsigned IsWeak : 1;<br>
unsigned MostConstrainingVisibility : 2;<br>
unsigned IsUsedInRegularObj : 1;<br>
unsigned IsUsedInDynamicReloc : 1;<br>
@@ -282,6 +282,9 @@ public:<br>
// was already returned.<br>
std::unique_ptr<InputFile> getMember();<br>
<br>
+ void setWeak() { IsWeak = true; }<br>
+ void setUsedInRegularObj() { IsUsedInRegularObj = true; }<br>
+<br>
private:<br>
ArchiveFile *File;<br>
const llvm::object::Archive::Symbol Sym;<br>
<br>
Added: lld/trunk/test/elf2/Inputs/archive3.s<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/lld/trunk/test/elf2/Inputs/archive3.s?rev=249406&view=auto" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/lld/trunk/test/elf2/Inputs/archive3.s?rev=249406&view=auto</a><br>
==============================================================================<br>
--- lld/trunk/test/elf2/Inputs/archive3.s (added)<br>
+++ lld/trunk/test/elf2/Inputs/archive3.s Tue Oct 6 09:33:58 2015<br>
@@ -0,0 +1,2 @@<br>
+.global bar<br>
+bar:<br>
<br>
Added: lld/trunk/test/elf2/Inputs/archive4.s<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/lld/trunk/test/elf2/Inputs/archive4.s?rev=249406&view=auto" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/lld/trunk/test/elf2/Inputs/archive4.s?rev=249406&view=auto</a><br>
==============================================================================<br>
--- lld/trunk/test/elf2/Inputs/archive4.s (added)<br>
+++ lld/trunk/test/elf2/Inputs/archive4.s Tue Oct 6 09:33:58 2015<br>
@@ -0,0 +1 @@<br>
+.quad bar<br>
<br>
Modified: lld/trunk/test/elf2/archive.s<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/lld/trunk/test/elf2/archive.s?rev=249406&r1=249405&r2=249406&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/lld/trunk/test/elf2/archive.s?rev=249406&r1=249405&r2=249406&view=diff</a><br>
==============================================================================<br>
--- lld/trunk/test/elf2/archive.s (original)<br>
+++ lld/trunk/test/elf2/archive.s Tue Oct 6 09:33:58 2015<br>
@@ -1,8 +1,10 @@<br>
# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t<br>
# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %S/Inputs/archive.s -o %t2<br>
# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %S/Inputs/archive2.s -o %t3<br>
-# RUN: llvm-ar rcs %tar %t2 %t3<br>
-# RUN: lld -flavor gnu2 %t %tar -o %tout<br>
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %S/Inputs/archive3.s -o %t4<br>
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %S/Inputs/archive4.s -o %t5<br>
+# RUN: llvm-ar rcs %tar %t2 %t3 %t4<br>
+# RUN: lld -flavor gnu2 %t %tar %t5 -o %tout<br>
# RUN: llvm-nm %tout | FileCheck %s<br>
# REQUIRES: x86<br>
<br>
@@ -13,6 +15,11 @@<br>
.weak foo<br>
.quad foo<br>
<br>
-# CHECK: T _start<br>
-# CHECK: T end<br>
-# CHECK: w foo<br>
+.weak bar<br>
+.quad bar<br>
+<br>
+<br>
+# CHECK: T _start<br>
+# CHECK-NEXT: T bar<br>
+# CHECK-NEXT: T end<br>
+# CHECK-NEXT: w foo<br>
<br>
<br>
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</blockquote></div><br></div>