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[JITLink] Add support for MachO .alt_entry atoms. 

The MachO .alt_entry directive is applied to a symbol to indicate that it is
locked (in terms of address layout and liveness) to its predecessor atom. I.e.
it is an alternate entry point, at a fixed offset, for the previous atom.

This patch updates MachOAtomGraphBuilder to check for the .alt_entry flag on
symbols and add a corresponding LayoutNext edge to the atom-graph. It also
updates MachOAtomGraphBuilder_x86_64 to generalize handling of the
X86_64_RELOC_SUBTRACTOR relocation: previously either the minuend or
subtrahend of the subtraction had to be the same as the atom being fixed up,
now it is only necessary for the minuend or subtrahend to be locked (via any
chain of alt_entry directives) to the atom being fixed up.

llvm-svn: 360194
This commit is contained in:
Lang Hames 2019-05-07 21:35:14 +00:00
parent b2fa002c83
commit 2b09b25e48
4 changed files with 173 additions and 12 deletions
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109
llvm/lib/ExecutionEngine/JITLink/MachOAtomGraphBuilder.cpp
View File

@ -44,6 +44,33 @@ void MachOAtomGraphBuilder::addCustomAtomizer(StringRef SectionName,
CustomAtomizeFunctions[SectionName] = std::move(Atomizer);
}
bool MachOAtomGraphBuilder::areLayoutLocked(const Atom &A, const Atom &B) {
// If these atoms are the same then they're trivially "locked".
if (&A == &B)
return true;
// If A and B are different, check whether either is undefined. (in which
// case they are not locked).
if (!A.isDefined() || !B.isDefined())
return false;
// A and B are different, but they're both defined atoms. We need to check
// whether they're part of the same alt_entry chain.
auto &DA = static_cast<const DefinedAtom &>(A);
auto &DB = static_cast<const DefinedAtom &>(B);
auto AStartItr = AltEntryStarts.find(&DA);
if (AStartItr == AltEntryStarts.end()) // If A is not in a chain bail out.
return false;
auto BStartItr = AltEntryStarts.find(&DB);
if (BStartItr == AltEntryStarts.end()) // If B is not in a chain bail out.
return false;
// A and B are layout locked if they're in the same chain.
return AStartItr->second == BStartItr->second;
}
unsigned
MachOAtomGraphBuilder::getPointerSize(const object::MachOObjectFile &Obj) {
return Obj.is64Bit() ? 8 : 4;
@ -126,6 +153,9 @@ Error MachOAtomGraphBuilder::addNonCustomAtoms() {
DenseMap<MachOSection *, AddrToAtomMap> SecToAtoms;
DenseMap<MachOSection *, unsigned> FirstOrdinal;
std::vector<DefinedAtom *> AltEntryAtoms;
DenseSet<StringRef> ProcessedSymbols; // Used to check for duplicate defs.
for (auto SymI = Obj.symbol_begin(), SymE = Obj.symbol_end(); SymI != SymE;
++SymI) {
@ -135,6 +165,14 @@ Error MachOAtomGraphBuilder::addNonCustomAtoms() {
if (!Name)
return Name.takeError();
// Bail out on duplicate definitions: There should never be more than one
// definition for a symbol in a given object file.
if (ProcessedSymbols.count(*Name))
return make_error<JITLinkError>("Duplicate definition within object: " +
*Name);
else
ProcessedSymbols.insert(*Name);
auto Addr = Sym.getAddress();
if (!Addr)
return Addr.takeError();
@ -189,24 +227,35 @@ Error MachOAtomGraphBuilder::addNonCustomAtoms() {
auto &Sec = SecByIndexItr->second;
auto &A = G->addDefinedAtom(Sec.getGenericSection(), *Name, *Addr,
std::max(Sym.getAlignment(), 1U));
auto &DA = G->addDefinedAtom(Sec.getGenericSection(), *Name, *Addr,
std::max(Sym.getAlignment(), 1U));
A.setGlobal(Flags & object::SymbolRef::SF_Global);
A.setExported(Flags & object::SymbolRef::SF_Exported);
A.setWeak(Flags & object::SymbolRef::SF_Weak);
DA.setGlobal(Flags & object::SymbolRef::SF_Global);
DA.setExported(Flags & object::SymbolRef::SF_Exported);
DA.setWeak(Flags & object::SymbolRef::SF_Weak);
A.setCallable(*SymType & object::SymbolRef::ST_Function);
DA.setCallable(*SymType & object::SymbolRef::ST_Function);
// Check alt-entry.
{
uint16_t NDesc = 0;
if (Obj.is64Bit())
NDesc = Obj.getSymbolTableEntry(SymI->getRawDataRefImpl()).n_desc;
else
NDesc = Obj.getSymbolTableEntry(SymI->getRawDataRefImpl()).n_desc;
if (NDesc & MachO::N_ALT_ENTRY)
AltEntryAtoms.push_back(&DA);
}
LLVM_DEBUG({
dbgs() << " Added " << *Name
<< " addr: " << format("0x%016" PRIx64, *Addr)
<< ", align: " << A.getAlignment()
<< ", align: " << DA.getAlignment()
<< ", section: " << Sec.getGenericSection().getName() << "\n";
});
auto &SecAtoms = SecToAtoms[&Sec];
SecAtoms[A.getAddress() - Sec.getAddress()] = &A;
SecAtoms[DA.getAddress() - Sec.getAddress()] = &DA;
}
// Add anonymous atoms.
@ -263,6 +312,50 @@ Error MachOAtomGraphBuilder::addNonCustomAtoms() {
}
}
LLVM_DEBUG(dbgs() << "Adding alt-entry starts\n");
// Sort alt-entry atoms by address in ascending order.
llvm::sort(AltEntryAtoms.begin(), AltEntryAtoms.end(),
[](const DefinedAtom *LHS, const DefinedAtom *RHS) {
return LHS->getAddress() < RHS->getAddress();
});
// Process alt-entry atoms in address order to build the table of alt-entry
// atoms to alt-entry chain starts.
for (auto *DA : AltEntryAtoms) {
assert(!AltEntryStarts.count(DA) && "Duplicate entry in AltEntryStarts");
// DA is an alt-entry atom. Look for the predecessor atom that it is locked
// to, bailing out if we do not find one.
auto AltEntryPred = G->findAtomByAddress(DA->getAddress() - 1);
if (!AltEntryPred)
return AltEntryPred.takeError();
// Add a LayoutNext edge from the predecessor to this atom.
AltEntryPred->addEdge(Edge::LayoutNext, 0, *DA, 0);
// Check to see whether the predecessor itself is an alt-entry atom.
auto AltEntryStartItr = AltEntryStarts.find(&*AltEntryPred);
if (AltEntryStartItr != AltEntryStarts.end()) {
// If the predecessor was an alt-entry atom then re-use its value.
AltEntryStarts[DA] = AltEntryStartItr->second;
LLVM_DEBUG({
dbgs() << " " << *DA << " -> " << *AltEntryStartItr->second
<< " (based on existing entry for " << *AltEntryPred << ")\n";
});
} else {
// If the predecessor does not have an entry then add an entry for this
// atom (i.e. the alt_entry atom) and a self-reference entry for the
/// predecessory atom that is the start of this chain.
AltEntryStarts[&*AltEntryPred] = &*AltEntryPred;
AltEntryStarts[DA] = &*AltEntryPred;
LLVM_DEBUG({
dbgs() << " " << *AltEntryPred << " -> " << *AltEntryPred << "\n"
<< " " << *DA << " -> " << *AltEntryPred << "\n";
});
}
}
return Error::success();
}

5
llvm/lib/ExecutionEngine/JITLink/MachOAtomGraphBuilder.h
View File

@ -96,6 +96,10 @@ protected:
virtual Error addRelocations() = 0;
/// Returns true if Atom A and Atom B are at a fixed offset from one another
/// (i.e. if they're part of the same alt-entry chain).
bool areLayoutLocked(const Atom &A, const Atom &B);
private:
static unsigned getPointerSize(const object::MachOObjectFile &Obj);
static support::endianness getEndianness(const object::MachOObjectFile &Obj);
@ -108,6 +112,7 @@ private:
const object::MachOObjectFile &Obj;
std::unique_ptr<AtomGraph> G;
DenseMap<const DefinedAtom *, const DefinedAtom *> AltEntryStarts;
DenseMap<unsigned, MachOSection> Sections;
StringMap<CustomAtomizeFunction> CustomAtomizeFunctions;
Optional<MachOSection> CommonSymbolsSection;

7
llvm/lib/ExecutionEngine/JITLink/MachO_x86_64.cpp
View File

@ -181,19 +181,20 @@ private:
MachOX86RelocationKind DeltaKind;
Atom *TargetAtom;
uint64_t Addend;
if (&AtomToFix == &*FromAtom) {
if (areLayoutLocked(AtomToFix, *FromAtom)) {
TargetAtom = ToAtom;
DeltaKind = (SubRI.r_length == 3) ? Delta64 : Delta32;
Addend = FixupValue + (FixupAddress - FromAtom->getAddress());
// FIXME: handle extern 'from'.
} else if (&AtomToFix == ToAtom) {
} else if (areLayoutLocked(AtomToFix, *ToAtom)) {
TargetAtom = &*FromAtom;
DeltaKind = (SubRI.r_length == 3) ? NegDelta64 : NegDelta32;
Addend = FixupValue - (FixupAddress - ToAtom->getAddress());
} else {
// AtomToFix was neither FromAtom nor ToAtom.
return make_error<JITLinkError>("SUBTRACTOR relocation must fix up "
"either 'A' or 'B'");
"either 'A' or 'B' (or an atom in one "
"of their alt-entry groups)");
}
return PairRelocInfo(DeltaKind, TargetAtom, Addend);

64
llvm/test/ExecutionEngine/JITLink/X86/MachO_x86-64_relocations.s
View File

@ -129,13 +129,19 @@ Lanon_minuend_quad:
Lanon_minuend_long:
.long Lanon_minuend_long - named_data + 2
# Named quad storage target (first named atom in __data).
.globl named_data
.p2align 3
named_data:
.quad 0x2222222222222222
# An alt-entry point for named_data
.globl named_data_alt_entry
.p2align 3
.alt_entry named_data_alt_entry
named_data_alt_entry:
.quad 0
# Check X86_64_RELOC_UNSIGNED / extern handling by putting the address of a
# local named function in a pointer variable.
#
@ -201,4 +207,60 @@ minuend_quad3:
minuend_long3:
.long minuend_long3 - named_data + 2
# Check X86_64_RELOC_SUBTRACTOR handling for exprs of the form
# "A: .quad/long B - C + D", where 'B' or 'C' is at a fixed offset from 'A'
# (i.e. is part of an alt_entry chain that includes 'A').
#
# Check "A: .long B - C + D" where 'B' is an alt_entry for 'A'.
# jitlink-check: *{4}subtractor_with_alt_entry_minuend_long = (subtractor_with_alt_entry_minuend_long_B - named_data + 2)[31:0]
.globl subtractor_with_alt_entry_minuend_long
.p2align 2
subtractor_with_alt_entry_minuend_long:
.long subtractor_with_alt_entry_minuend_long_B - named_data + 2
.globl subtractor_with_alt_entry_minuend_long_B
.p2align 2
.alt_entry subtractor_with_alt_entry_minuend_long_B
subtractor_with_alt_entry_minuend_long_B:
.long 0
# Check "A: .quad B - C + D" where 'B' is an alt_entry for 'A'.
# jitlink-check: *{8}subtractor_with_alt_entry_minuend_quad = (subtractor_with_alt_entry_minuend_quad_B - named_data + 2)
.globl subtractor_with_alt_entry_minuend_quad
.p2align 3
subtractor_with_alt_entry_minuend_quad:
.quad subtractor_with_alt_entry_minuend_quad_B - named_data + 2
.globl subtractor_with_alt_entry_minuend_quad_B
.p2align 3
.alt_entry subtractor_with_alt_entry_minuend_quad_B
subtractor_with_alt_entry_minuend_quad_B:
.quad 0
# Check "A: .long B - C + D" where 'C' is an alt_entry for 'A'.
# jitlink-check: *{4}subtractor_with_alt_entry_subtrahend_long = (named_data - subtractor_with_alt_entry_subtrahend_long_B + 2)[31:0]
.globl subtractor_with_alt_entry_subtrahend_long
.p2align 2
subtractor_with_alt_entry_subtrahend_long:
.long named_data - subtractor_with_alt_entry_subtrahend_long_B + 2
.globl subtractor_with_alt_entry_subtrahend_long_B
.p2align 2
.alt_entry subtractor_with_alt_entry_subtrahend_long_B
subtractor_with_alt_entry_subtrahend_long_B:
.long 0
# Check "A: .quad B - C + D" where 'B' is an alt_entry for 'A'.
# jitlink-check: *{8}subtractor_with_alt_entry_subtrahend_quad = (named_data - subtractor_with_alt_entry_subtrahend_quad_B + 2)
.globl subtractor_with_alt_entry_subtrahend_quad
.p2align 3
subtractor_with_alt_entry_subtrahend_quad:
.quad named_data - subtractor_with_alt_entry_subtrahend_quad_B + 2
.globl subtractor_with_alt_entry_subtrahend_quad_B
.p2align 3
.alt_entry subtractor_with_alt_entry_subtrahend_quad_B
subtractor_with_alt_entry_subtrahend_quad_B:
.quad 0
.subsections_via_symbols