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Sort common symbols by alignment. 

llvm-svn: 246511
This commit is contained in:
Rafael Espindola 2015-09-01 00:16:38 +00:00
parent 65e1e4dbe0
commit b56cb9437f
2 changed files with 27 additions and 4 deletions
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20
lld/ELF/Writer.cpp
View File

@ -408,6 +408,12 @@ template <bool Is64Bits> struct DenseMapInfo<SectionKey<Is64Bits>> {
};
}
template <class ELFT>
static bool cmpAlign(const DefinedCommon<ELFT> *A,
const DefinedCommon<ELFT> *B) {
return A->Sym.st_value > B->Sym.st_value;
}
// Create output section objects and add them to OutputSections.
template <class ELFT> void Writer<ELFT>::createSections() {
SmallDenseMap<SectionKey<ELFT::Is64Bits>, OutputSection<ELFT> *> Map;
@ -438,19 +444,25 @@ template <class ELFT> void Writer<ELFT>::createSections() {
SymTable.BSSSec = getSection(".bss", SHT_NOBITS, SHF_ALLOC | SHF_WRITE);
OutputSection<ELFT> *BSSSec = SymTable.BSSSec;
uintX_t Off = BSSSec->getSize();
// FIXME: Try to avoid the extra walk over all global symbols.
std::vector<DefinedCommon<ELFT> *> CommonSymbols;
for (auto &P : Symtab.getSymbols()) {
SymbolBody *Body = P.second->Body;
auto *C = dyn_cast<DefinedCommon<ELFT>>(Body);
if (!C)
continue;
if (auto *C = dyn_cast<DefinedCommon<ELFT>>(Body))
CommonSymbols.push_back(C);
}
// Sort the common symbols by alignment as an heuristic to pack them better.
std::stable_sort(CommonSymbols.begin(), CommonSymbols.end(), cmpAlign<ELFT>);
uintX_t Off = BSSSec->getSize();
for (DefinedCommon<ELFT> *C : CommonSymbols) {
const Elf_Sym &Sym = C->Sym;
uintX_t Align = Sym.st_value;
Off = RoundUpToAlignment(Off, Align);
C->OffsetInBSS = Off;
Off += Sym.st_size;
}
BSSSec->setSize(Off);
}

11
lld/test/elf2/common.s
View File

@ -11,8 +11,18 @@
// CHECK-NEXT: SHF_WRITE
// CHECK-NEXT: ]
// CHECK-NEXT: Address: 0x1000
// CHECK-NEXT: Offset:
// CHECK-NEXT: Size: 18
// CHECK: Name: sym3
// CHECK-NEXT: Value: 0x1010
// CHECK-NEXT: Size: 2
// CHECK-NEXT: Binding: Global
// CHECK-NEXT: Type: Object
// CHECK-NEXT: Other: 0
// CHECK-NEXT: Section: .bss
// CHECK: Name: sym2
// CHECK-NEXT: Value: 0x1008
// CHECK-NEXT: Size: 8
@ -35,3 +45,4 @@ _start:
.comm sym1,4,4
.comm sym2,8,4
.comm sym3,2,2