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//===---- llvm-jitlink-elf.cpp -- ELF parsing support for llvm-jitlink ----===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// ELF parsing support for llvm-jitlink.
//
//===----------------------------------------------------------------------===//
#include "llvm-jitlink.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/Path.h"
#define DEBUG_TYPE "llvm_jitlink"
using namespace llvm;
using namespace llvm::jitlink;
static bool isELFGOTSection(Section &S) { return S.getName() == "$__GOT"; }
static bool isELFStubsSection(Section &S) { return S.getName() == "$__STUBS"; }
static bool isELFAArch32StubsSection(Section &S) {
return S.getName().starts_with("__llvm_jitlink_aarch32_STUBS_");
}
static Expected<Edge &> getFirstRelocationEdge(LinkGraph &G, Block &B) {
auto EItr =
llvm::find_if(B.edges(), [](Edge &E) { return E.isRelocation(); });
if (EItr == B.edges().end())
return make_error<StringError>("GOT entry in " + G.getName() + ", \"" +
B.getSection().getName() +
"\" has no relocations",
inconvertibleErrorCode());
return *EItr;
}
static Expected<Symbol &> getELFGOTTarget(LinkGraph &G, Block &B) {
auto E = getFirstRelocationEdge(G, B);
if (!E)
return E.takeError();
auto &TargetSym = E->getTarget();
if (!TargetSym.hasName())
return make_error<StringError>(
"GOT entry in " + G.getName() + ", \"" +
TargetSym.getBlock().getSection().getName() +
"\" points to anonymous "
"symbol",
inconvertibleErrorCode());
return TargetSym;
}
static Expected<Symbol &> getELFStubTarget(LinkGraph &G, Block &B) {
auto E = getFirstRelocationEdge(G, B);
if (!E)
return E.takeError();
auto &GOTSym = E->getTarget();
if (!GOTSym.isDefined())
return make_error<StringError>("Stubs entry in " + G.getName() +
" does not point to GOT entry",
inconvertibleErrorCode());
if (!isELFGOTSection(GOTSym.getBlock().getSection()))
return make_error<StringError>(
"Stubs entry in " + G.getName() + ", \"" +
GOTSym.getBlock().getSection().getName() +
"\" does not point to GOT entry",
inconvertibleErrorCode());
return getELFGOTTarget(G, GOTSym.getBlock());
}
static Expected<Symbol &> getELFAArch32StubTarget(LinkGraph &G, Block &B) {
auto E = getFirstRelocationEdge(G, B);
if (!E)
return E.takeError();
return E->getTarget();
}
enum SectionType { GOT, Stubs, AArch32Stubs, Other };
static Error registerSymbol(LinkGraph &G, Symbol &Sym, Session::FileInfo &FI,
SectionType SecType) {
switch (SecType) {
case GOT:
if (Sym.getSize() == 0)
return Error::success(); // Skip the GOT start symbol
return FI.registerGOTEntry(G, Sym, getELFGOTTarget);
case Stubs:
return FI.registerStubEntry(G, Sym, getELFStubTarget);
case AArch32Stubs:
return FI.registerMultiStubEntry(G, Sym, getELFAArch32StubTarget);
case Other:
return Error::success();
}
llvm_unreachable("Unhandled SectionType enum");
}
namespace llvm {
Error registerELFGraphInfo(Session &S, LinkGraph &G) {
std::lock_guard<std::mutex> Lock(S.M);
auto FileName = sys::path::filename(G.getName());
auto [It, Inserted] = S.FileInfos.try_emplace(FileName);
if (!Inserted) {
return make_error<StringError>("When -check is passed, file names must be "
"distinct (duplicate: \"" +
FileName + "\")",
inconvertibleErrorCode());
}
auto &FileInfo = It->second;
LLVM_DEBUG({
dbgs() << "Registering ELF file info for \"" << FileName << "\"\n";
});
for (auto &Sec : G.sections()) {
LLVM_DEBUG({
dbgs() << " Section \"" << Sec.getName() << "\": "
<< (Sec.symbols().empty() ? "empty. skipping." : "processing...")
<< "\n";
});
// Skip empty sections.
if (Sec.symbols().empty())
continue;
if (FileInfo.SectionInfos.count(Sec.getName()))
return make_error<StringError>("Encountered duplicate section name \"" +
Sec.getName() + "\" in \"" + FileName +
"\"",
inconvertibleErrorCode());
SectionType SecType;
if (isELFGOTSection(Sec)) {
SecType = GOT;
} else if (isELFStubsSection(Sec)) {
SecType = Stubs;
} else if (isELFAArch32StubsSection(Sec)) {
SecType = AArch32Stubs;
} else {
SecType = Other;
}
bool SectionContainsContent = false;
bool SectionContainsZeroFill = false;
auto *FirstSym = *Sec.symbols().begin();
auto *LastSym = FirstSym;
for (auto *Sym : Sec.symbols()) {
if (Sym->getAddress() < FirstSym->getAddress())
FirstSym = Sym;
if (Sym->getAddress() > LastSym->getAddress())
LastSym = Sym;
if (SecType != Other) {
if (Error Err = registerSymbol(G, *Sym, FileInfo, SecType))
return Err;
SectionContainsContent = true;
}
if (Sym->hasName()) {
if (Sym->isSymbolZeroFill()) {
S.SymbolInfos[Sym->getName()] = {Sym->getSize(),
Sym->getAddress().getValue()};
SectionContainsZeroFill = true;
} else {
S.SymbolInfos[Sym->getName()] = {Sym->getSymbolContent(),
Sym->getAddress().getValue(),
Sym->getTargetFlags()};
SectionContainsContent = true;
}
}
}
// Add symbol info for absolute symbols.
for (auto *Sym : G.absolute_symbols())
S.SymbolInfos[Sym->getName()] = {Sym->getSize(),
Sym->getAddress().getValue()};
auto SecAddr = FirstSym->getAddress();
auto SecSize =
(LastSym->getBlock().getAddress() + LastSym->getBlock().getSize()) -
SecAddr;
if (SectionContainsZeroFill && SectionContainsContent)
return make_error<StringError>("Mixed zero-fill and content sections not "
"supported yet",
inconvertibleErrorCode());
if (SectionContainsZeroFill)
FileInfo.SectionInfos[Sec.getName()] = {SecSize, SecAddr.getValue()};
else
FileInfo.SectionInfos[Sec.getName()] = {
ArrayRef<char>(FirstSym->getBlock().getContent().data(), SecSize),
SecAddr.getValue(), FirstSym->getTargetFlags()};
}
return Error::success();
}
} // end namespace llvm
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