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[JITLink][ELF] Support duplicated section names from object file
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ELF object files can contain duplicated sections (thus section symbols
as well), espeically when comdats/section groups are present. This patch
adds support for generating LinkGraph from object files that have
duplicated section names. This is the first step to properly model
comdats/section groups.

Reviewed By: lhames

Differential Revision: https://reviews.llvm.org/D114753
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@cachemeifyoucan
cachemeifyoucan committed Jan 18, 2022
1 parent 347d4d7 commit 091e364
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Showing 5 changed files with 72 additions and 49 deletions.
67 changes: 33 additions & 34 deletions llvm/lib/ExecutionEngine/JITLink/ELFLinkGraphBuilder.h
View file
Expand Up @@ -77,14 +77,14 @@ class ELFLinkGraphBuilder : public ELFLinkGraphBuilderBase {
return Obj.getHeader().e_type == llvm::ELF::ET_REL;
}

void setGraphSection(ELFSectionIndex SecIndex, Section &Sec) {
assert(!GraphSections.count(SecIndex) && "Duplicate section at index");
GraphSections[SecIndex] = &Sec;
void setGraphBlock(ELFSectionIndex SecIndex, Block *B) {
assert(!GraphBlocks.count(SecIndex) && "Duplicate section at index");
GraphBlocks[SecIndex] = B;
}

Section *getGraphSection(ELFSectionIndex SecIndex) {
auto I = GraphSections.find(SecIndex);
if (I == GraphSections.end())
Block *getGraphBlock(ELFSectionIndex SecIndex) {
auto I = GraphBlocks.find(SecIndex);
if (I == GraphBlocks.end())
return nullptr;
return I->second;
}
Expand Down Expand Up @@ -139,9 +139,9 @@ class ELFLinkGraphBuilder : public ELFLinkGraphBuilderBase {
const typename ELFFile::Elf_Shdr *SymTabSec = nullptr;
StringRef SectionStringTab;

// Maps ELF section indexes to LinkGraph Sections.
// Only SHF_ALLOC sections will have graph sections.
DenseMap<ELFSectionIndex, Section *> GraphSections;
// Maps ELF section indexes to LinkGraph Blocks.
// Only SHF_ALLOC sections will have graph blocks.
DenseMap<ELFSectionIndex, Block *> GraphBlocks;
DenseMap<ELFSymbolIndex, Symbol *> GraphSymbols;
DenseMap<const typename ELFFile::Elf_Shdr *,
ArrayRef<typename ELFFile::Elf_Word>>
Expand Down Expand Up @@ -316,20 +316,27 @@ template <typename ELFT> Error ELFLinkGraphBuilder<ELFT>::graphifySections() {
else
Prot = MemProt::Read | MemProt::Write;

auto &GraphSec = G->createSection(*Name, Prot);
// Look for existing sections first.
auto *GraphSec = G->findSectionByName(*Name);
if (!GraphSec)
GraphSec = &G->createSection(*Name, Prot);
assert(GraphSec->getMemProt() == Prot && "MemProt should match");

Block *B = nullptr;
if (Sec.sh_type != ELF::SHT_NOBITS) {
auto Data = Obj.template getSectionContentsAsArray<char>(Sec);
if (!Data)
return Data.takeError();

G->createContentBlock(GraphSec, *Data, orc::ExecutorAddr(Sec.sh_addr),
Sec.sh_addralign, 0);
B = &G->createContentBlock(*GraphSec, *Data,
orc::ExecutorAddr(Sec.sh_addr),
Sec.sh_addralign, 0);
} else
G->createZeroFillBlock(GraphSec, Sec.sh_size,
orc::ExecutorAddr(Sec.sh_addr), Sec.sh_addralign,
0);
B = &G->createZeroFillBlock(*GraphSec, Sec.sh_size,
orc::ExecutorAddr(Sec.sh_addr),
Sec.sh_addralign, 0);

setGraphSection(SecIndex, GraphSec);
setGraphBlock(SecIndex, B);
}

return Error::success();
Expand Down Expand Up @@ -427,28 +434,20 @@ template <typename ELFT> Error ELFLinkGraphBuilder<ELFT>::graphifySymbols() {
return NdxOrErr.takeError();
Shndx = *NdxOrErr;
}
if (auto *GraphSec = getGraphSection(Shndx)) {
Block *B = nullptr;
{
auto Blocks = GraphSec->blocks();
assert(Blocks.begin() != Blocks.end() && "No blocks for section");
assert(std::next(Blocks.begin()) == Blocks.end() &&
"Multiple blocks for section");
B = *Blocks.begin();
}

if (auto *B = getGraphBlock(Shndx)) {
LLVM_DEBUG({
dbgs() << " " << SymIndex
<< ": Creating defined graph symbol for ELF symbol \"" << *Name
<< "\"\n";
});

if (Sym.getType() == ELF::STT_SECTION)
*Name = GraphSec->getName();

// Model the section symbols as anonymous symbol.
auto &GSym =
G->addDefinedSymbol(*B, Sym.getValue(), *Name, Sym.st_size, L, S,
Sym.getType() == ELF::STT_FUNC, false);
Sym.getType() == ELF::STT_SECTION
? G->addAnonymousSymbol(*B, Sym.getValue(), Sym.st_size, false,
false)
: G->addDefinedSymbol(*B, Sym.getValue(), *Name, Sym.st_size, L,
S, Sym.getType() == ELF::STT_FUNC, false);
setGraphSymbol(SymIndex, GSym);
}
} else if (Sym.isUndefined() && Sym.isExternal()) {
Expand Down Expand Up @@ -500,8 +499,8 @@ Error ELFLinkGraphBuilder<ELFT>::forEachRelocation(
}

// Lookup the link-graph node corresponding to the target section name.
Section *GraphSect = G->findSectionByName(*Name);
if (!GraphSect)
auto *BlockToFix = getGraphBlock(RelSect.sh_info);
if (!BlockToFix)
return make_error<StringError>(
"Refencing a section that wasn't added to the graph: " + *Name,
inconvertibleErrorCode());
Expand All @@ -512,7 +511,7 @@ Error ELFLinkGraphBuilder<ELFT>::forEachRelocation(

// Let the callee process relocation entries one by one.
for (const typename ELFT::Rela &R : *RelEntries)
if (Error Err = Func(R, **FixupSection, *GraphSect))
if (Error Err = Func(R, **FixupSection, *BlockToFix))
return Err;

LLVM_DEBUG(dbgs() << "\n");
Expand Down
9 changes: 4 additions & 5 deletions llvm/lib/ExecutionEngine/JITLink/ELF_aarch64.cpp
View file
Expand Up @@ -101,7 +101,7 @@ class ELFLinkGraphBuilder_aarch64 : public ELFLinkGraphBuilder<ELFT> {

Error addSingleRelocation(const typename ELFT::Rela &Rel,
const typename ELFT::Shdr &FixupSect,
Section &GraphSection) {
Block &BlockToFix) {
using Base = ELFLinkGraphBuilder<ELFT>;

uint32_t SymbolIndex = Rel.getSymbol(false);
Expand All @@ -124,18 +124,17 @@ class ELFLinkGraphBuilder_aarch64 : public ELFLinkGraphBuilder<ELFT> {
return Kind.takeError();

int64_t Addend = Rel.r_addend;
Block *BlockToFix = *(GraphSection.blocks().begin());
orc::ExecutorAddr FixupAddress =
orc::ExecutorAddr(FixupSect.sh_addr) + Rel.r_offset;
Edge::OffsetT Offset = FixupAddress - BlockToFix->getAddress();
Edge::OffsetT Offset = FixupAddress - BlockToFix.getAddress();
Edge GE(*Kind, Offset, *GraphSymbol, Addend);
LLVM_DEBUG({
dbgs() << " ";
printEdge(dbgs(), *BlockToFix, GE, aarch64::getEdgeKindName(*Kind));
printEdge(dbgs(), BlockToFix, GE, aarch64::getEdgeKindName(*Kind));
dbgs() << "\n";
});

BlockToFix->addEdge(std::move(GE));
BlockToFix.addEdge(std::move(GE));
return Error::success();
}

Expand Down
9 changes: 4 additions & 5 deletions llvm/lib/ExecutionEngine/JITLink/ELF_riscv.cpp
View file
Expand Up @@ -349,7 +349,7 @@ class ELFLinkGraphBuilder_riscv : public ELFLinkGraphBuilder<ELFT> {

Error addSingleRelocation(const typename ELFT::Rela &Rel,
const typename ELFT::Shdr &FixupSect,
Section &GraphSection) {
Block &BlockToFix) {
using Base = ELFLinkGraphBuilder<ELFT>;

uint32_t SymbolIndex = Rel.getSymbol(false);
Expand All @@ -372,17 +372,16 @@ class ELFLinkGraphBuilder_riscv : public ELFLinkGraphBuilder<ELFT> {
return Kind.takeError();

int64_t Addend = Rel.r_addend;
Block *BlockToFix = *(GraphSection.blocks().begin());
auto FixupAddress = orc::ExecutorAddr(FixupSect.sh_addr) + Rel.r_offset;
Edge::OffsetT Offset = FixupAddress - BlockToFix->getAddress();
Edge::OffsetT Offset = FixupAddress - BlockToFix.getAddress();
Edge GE(*Kind, Offset, *GraphSymbol, Addend);
LLVM_DEBUG({
dbgs() << " ";
printEdge(dbgs(), *BlockToFix, GE, riscv::getEdgeKindName(*Kind));
printEdge(dbgs(), BlockToFix, GE, riscv::getEdgeKindName(*Kind));
dbgs() << "\n";
});

BlockToFix->addEdge(std::move(GE));
BlockToFix.addEdge(std::move(GE));
return Error::success();
}

Expand Down
9 changes: 4 additions & 5 deletions llvm/lib/ExecutionEngine/JITLink/ELF_x86_64.cpp
View file
Expand Up @@ -172,7 +172,7 @@ class ELFLinkGraphBuilder_x86_64 : public ELFLinkGraphBuilder<object::ELF64LE> {

Error addSingleRelocation(const typename ELFT::Rela &Rel,
const typename ELFT::Shdr &FixupSection,
Section &GraphSection) {
Block &BlockToFix) {
using Base = ELFLinkGraphBuilder<ELFT>;

uint32_t SymbolIndex = Rel.getSymbol(false);
Expand Down Expand Up @@ -248,17 +248,16 @@ class ELFLinkGraphBuilder_x86_64 : public ELFLinkGraphBuilder<object::ELF64LE> {
}
}

Block *BlockToFix = *(GraphSection.blocks().begin());
auto FixupAddress = orc::ExecutorAddr(FixupSection.sh_addr) + Rel.r_offset;
Edge::OffsetT Offset = FixupAddress - BlockToFix->getAddress();
Edge::OffsetT Offset = FixupAddress - BlockToFix.getAddress();
Edge GE(Kind, Offset, *GraphSymbol, Addend);
LLVM_DEBUG({
dbgs() << " ";
printEdge(dbgs(), *BlockToFix, GE, x86_64::getEdgeKindName(Kind));
printEdge(dbgs(), BlockToFix, GE, x86_64::getEdgeKindName(Kind));
dbgs() << "\n";
});

BlockToFix->addEdge(std::move(GE));
BlockToFix.addEdge(std::move(GE));
return Error::success();
}

Expand Down
27 changes: 27 additions & 0 deletions llvm/test/ExecutionEngine/JITLink/X86/ELF_comdat.s
View file
@@ -0,0 +1,27 @@
// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o %t
// RUN: llvm-jitlink -noexec %t

.section .foo,"axG",@progbits,g1,comdat
.globl g1
g1:
call test1
retq

.section .baz,"axG",@progbits,g1,comdat
test1:
retq

.section .bar,"axG",@progbits,g2,comdat
.globl g2
g2:
call test2
retq

.section .baz,"axG",@progbits,g2,comdat
test2:
retq

.text
.globl main
main:
retq

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