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//=== i386.h - Generic JITLink i386 edge kinds, utilities -*- C++ -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// Generic utilities for graphs representing i386 objects.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_EXECUTIONENGINE_JITLINK_I386_H
#define LLVM_EXECUTIONENGINE_JITLINK_I386_H
#include "llvm/ExecutionEngine/JITLink/JITLink.h"
#include "llvm/ExecutionEngine/JITLink/TableManager.h"
namespace llvm::jitlink::i386 {
/// Represets i386 fixups
enum EdgeKind_i386 : Edge::Kind {
/// None
None = Edge::FirstRelocation,
/// A plain 32-bit pointer value relocation.
///
/// Fixup expression:
/// Fixup <- Target + Addend : uint32
///
/// Errors:
/// - The target must reside in the low 32-bits of the address space,
/// otherwise an out-of-range error will be returned.
///
Pointer32,
/// A 32-bit PC-relative relocation.
///
/// Represents a data/control flow instruction using PC-relative addressing
/// to a target.
///
/// The fixup expression for this kind includes an implicit offset to account
/// for the PC (unlike the Delta edges) so that a PCRel32 with a target
/// T and addend zero is a call/branch to the start (offset zero) of T.
///
/// Fixup expression:
/// Fixup <- Target - (Fixup + 4) + Addend : int32
///
/// Errors:
/// - The result of the fixup expression must fit into an int32, otherwise
/// an out-of-range error will be returned.
///
PCRel32,
/// A plain 16-bit pointer value relocation.
///
/// Fixup expression:
/// Fixup <- Target + Addend : uint16
///
/// Errors:
/// - The target must reside in the low 16-bits of the address space,
/// otherwise an out-of-range error will be returned.
///
Pointer16,
/// A 16-bit PC-relative relocation.
///
/// Represents a data/control flow instruction using PC-relative addressing
/// to a target.
///
/// The fixup expression for this kind includes an implicit offset to account
/// for the PC (unlike the Delta edges) so that a PCRel16 with a target
/// T and addend zero is a call/branch to the start (offset zero) of T.
///
/// Fixup expression:
/// Fixup <- Target - (Fixup + 4) + Addend : int16
///
/// Errors:
/// - The result of the fixup expression must fit into an int16, otherwise
/// an out-of-range error will be returned.
///
PCRel16,
/// A 32-bit delta.
///
/// Delta from the fixup to the target.
///
/// Fixup expression:
/// Fixup <- Target - Fixup + Addend : int64
///
/// Errors:
/// - The result of the fixup expression must fit into an int32, otherwise
/// an out-of-range error will be returned.
Delta32,
/// A 32-bit GOT delta.
///
/// Delta from the global offset table to the target.
///
/// Fixup expression:
/// Fixup <- Target - GOTSymbol + Addend : int32
///
/// Errors:
/// - *ASSERTION* Failure to a null pointer GOTSymbol, which the GOT section
/// symbol was not been defined.
Delta32FromGOT,
/// A GOT entry offset within GOT getter/constructor, transformed to
/// Delta32FromGOT pointing at the GOT entry for the original target.
///
/// Indicates that this edge should be transformed into a Delta32FromGOT
/// targeting the GOT entry for the edge's current target, maintaining the
/// same addend.
/// A GOT entry for the target should be created if one does not already
/// exist.
///
/// Edges of this kind are usually handled by a GOT builder pass inserted by
/// default
///
/// Fixup expression:
/// NONE
///
/// Errors:
/// - *ASSERTION* Failure to handle edges of this kind prior to the fixup
/// phase will result in an assert/unreachable during the fixup phase
RequestGOTAndTransformToDelta32FromGOT,
/// A 32-bit PC-relative branch.
///
/// Represents a PC-relative call or branch to a target. This can be used to
/// identify, record, and/or patch call sites.
///
/// The fixup expression for this kind includes an implicit offset to account
/// for the PC (unlike the Delta edges) so that a Branch32PCRel with a target
/// T and addend zero is a call/branch to the start (offset zero) of T.
///
/// Fixup expression:
/// Fixup <- Target - (Fixup + 4) + Addend : int32
///
/// Errors:
/// - The result of the fixup expression must fit into an int32, otherwise
/// an out-of-range error will be returned.
///
BranchPCRel32,
/// A 32-bit PC-relative branch to a pointer jump stub.
///
/// The target of this relocation should be a pointer jump stub of the form:
///
/// \code{.s}
/// .text
/// jmp *tgtptr
/// ; ...
///
/// .data
/// tgtptr:
/// .quad 0
/// \endcode
///
/// This edge kind has the same fixup expression as BranchPCRel32, but further
/// identifies the call/branch as being to a pointer jump stub. For edges of
/// this kind the jump stub should not be bypassed (use
/// BranchPCRel32ToPtrJumpStubBypassable for that), but the pointer location
/// target may be recorded to allow manipulation at runtime.
///
/// Fixup expression:
/// Fixup <- Target - Fixup + Addend - 4 : int32
///
/// Errors:
/// - The result of the fixup expression must fit into an int32, otherwise
/// an out-of-range error will be returned.
///
BranchPCRel32ToPtrJumpStub,
/// A relaxable version of BranchPCRel32ToPtrJumpStub.
///
/// The edge kind has the same fixup expression as BranchPCRel32ToPtrJumpStub,
/// but identifies the call/branch as being to a pointer jump stub that may be
/// bypassed with a direct jump to the ultimate target if the ultimate target
/// is within range of the fixup location.
///
/// Fixup expression:
/// Fixup <- Target - Fixup + Addend - 4: int32
///
/// Errors:
/// - The result of the fixup expression must fit into an int32, otherwise
/// an out-of-range error will be returned.
///
BranchPCRel32ToPtrJumpStubBypassable,
};
/// Returns a string name for the given i386 edge. For debugging purposes
/// only
const char *getEdgeKindName(Edge::Kind K);
/// Apply fixup expression for edge to block content.
inline Error applyFixup(LinkGraph &G, Block &B, const Edge &E,
const Symbol *GOTSymbol) {
using namespace i386;
using namespace llvm::support;
char *BlockWorkingMem = B.getAlreadyMutableContent().data();
char *FixupPtr = BlockWorkingMem + E.getOffset();
auto FixupAddress = B.getAddress() + E.getOffset();
switch (E.getKind()) {
case i386::None: {
break;
}
case i386::Pointer32: {
uint32_t Value = E.getTarget().getAddress().getValue() + E.getAddend();
*(ulittle32_t *)FixupPtr = Value;
break;
}
case i386::PCRel32: {
int32_t Value =
E.getTarget().getAddress() - (FixupAddress + 4) + E.getAddend();
*(little32_t *)FixupPtr = Value;
break;
}
case i386::Pointer16: {
uint32_t Value = E.getTarget().getAddress().getValue() + E.getAddend();
if (LLVM_LIKELY(isUInt<16>(Value)))
*(ulittle16_t *)FixupPtr = Value;
else
return makeTargetOutOfRangeError(G, B, E);
break;
}
case i386::PCRel16: {
int32_t Value =
E.getTarget().getAddress() - (FixupAddress + 4) + E.getAddend();
if (LLVM_LIKELY(isInt<16>(Value)))
*(little16_t *)FixupPtr = Value;
else
return makeTargetOutOfRangeError(G, B, E);
break;
}
case i386::Delta32: {
int32_t Value = E.getTarget().getAddress() - FixupAddress + E.getAddend();
*(little32_t *)FixupPtr = Value;
break;
}
case i386::Delta32FromGOT: {
assert(GOTSymbol && "No GOT section symbol");
int32_t Value =
E.getTarget().getAddress() - GOTSymbol->getAddress() + E.getAddend();
*(little32_t *)FixupPtr = Value;
break;
}
case i386::BranchPCRel32:
case i386::BranchPCRel32ToPtrJumpStub:
case i386::BranchPCRel32ToPtrJumpStubBypassable: {
int32_t Value =
E.getTarget().getAddress() - (FixupAddress + 4) + E.getAddend();
*(little32_t *)FixupPtr = Value;
break;
}
default:
return make_error<JITLinkError>(
"In graph " + G.getName() + ", section " + B.getSection().getName() +
" unsupported edge kind " + getEdgeKindName(E.getKind()));
}
return Error::success();
}
/// i386 pointer size.
constexpr uint32_t PointerSize = 4;
/// i386 null pointer content.
extern const char NullPointerContent[PointerSize];
/// i386 pointer jump stub content.
///
/// Contains the instruction sequence for an indirect jump via an in-memory
/// pointer:
/// jmpq *ptr
extern const char PointerJumpStubContent[6];
/// Creates a new pointer block in the given section and returns an anonymous
/// symbol pointing to it.
///
/// If InitialTarget is given then an Pointer32 relocation will be added to the
/// block pointing at InitialTarget.
///
/// The pointer block will have the following default values:
/// alignment: 32-bit
/// alignment-offset: 0
/// address: highest allowable (~7U)
inline Symbol &createAnonymousPointer(LinkGraph &G, Section &PointerSection,
Symbol *InitialTarget = nullptr,
uint64_t InitialAddend = 0) {
auto &B = G.createContentBlock(PointerSection, NullPointerContent,
orc::ExecutorAddr(), 8, 0);
if (InitialTarget)
B.addEdge(Pointer32, 0, *InitialTarget, InitialAddend);
return G.addAnonymousSymbol(B, 0, PointerSize, false, false);
}
/// Create a jump stub block that jumps via the pointer at the given symbol.
///
/// The stub block will have the following default values:
/// alignment: 8-bit
/// alignment-offset: 0
/// address: highest allowable: (~5U)
inline Block &createPointerJumpStubBlock(LinkGraph &G, Section &StubSection,
Symbol &PointerSymbol) {
auto &B = G.createContentBlock(StubSection, PointerJumpStubContent,
orc::ExecutorAddr(), 8, 0);
B.addEdge(Pointer32,
// Offset is 2 because the the first 2 bytes of the
// jump stub block are {0xff, 0x25} -- an indirect absolute
// jump.
2, PointerSymbol, 0);
return B;
}
/// Create a jump stub that jumps via the pointer at the given symbol and
/// an anonymous symbol pointing to it. Return the anonymous symbol.
///
/// The stub block will be created by createPointerJumpStubBlock.
inline Symbol &createAnonymousPointerJumpStub(LinkGraph &G,
Section &StubSection,
Symbol &PointerSymbol) {
return G.addAnonymousSymbol(
createPointerJumpStubBlock(G, StubSection, PointerSymbol), 0, 6, true,
false);
}
/// Global Offset Table Builder.
class GOTTableManager : public TableManager<GOTTableManager> {
public:
static StringRef getSectionName() { return "$__GOT"; }
bool visitEdge(LinkGraph &G, Block *B, Edge &E) {
Edge::Kind KindToSet = Edge::Invalid;
switch (E.getKind()) {
case i386::Delta32FromGOT: {
// we need to make sure that the GOT section exists, but don't otherwise
// need to fix up this edge
getGOTSection(G);
return false;
}
case i386::RequestGOTAndTransformToDelta32FromGOT:
KindToSet = i386::Delta32FromGOT;
break;
default:
return false;
}
assert(KindToSet != Edge::Invalid &&
"Fell through switch, but no new kind to set");
DEBUG_WITH_TYPE("jitlink", {
dbgs() << " Fixing " << G.getEdgeKindName(E.getKind()) << " edge at "
<< B->getFixupAddress(E) << " (" << B->getAddress() << " + "
<< formatv("{0:x}", E.getOffset()) << ")\n";
});
E.setKind(KindToSet);
E.setTarget(getEntryForTarget(G, E.getTarget()));
return true;
}
Symbol &createEntry(LinkGraph &G, Symbol &Target) {
return createAnonymousPointer(G, getGOTSection(G), &Target);
}
private:
Section &getGOTSection(LinkGraph &G) {
if (!GOTSection)
GOTSection = &G.createSection(getSectionName(), orc::MemProt::Read);
return *GOTSection;
}
Section *GOTSection = nullptr;
};
/// Procedure Linkage Table Builder.
class PLTTableManager : public TableManager<PLTTableManager> {
public:
PLTTableManager(GOTTableManager &GOT) : GOT(GOT) {}
static StringRef getSectionName() { return "$__STUBS"; }
bool visitEdge(LinkGraph &G, Block *B, Edge &E) {
if (E.getKind() == i386::BranchPCRel32 && !E.getTarget().isDefined()) {
DEBUG_WITH_TYPE("jitlink", {
dbgs() << " Fixing " << G.getEdgeKindName(E.getKind()) << " edge at "
<< B->getFixupAddress(E) << " (" << B->getAddress() << " + "
<< formatv("{0:x}", E.getOffset()) << ")\n";
});
// Set the edge kind to Branch32ToPtrJumpStubBypassable to enable it to
// be optimized when the target is in-range.
E.setKind(i386::BranchPCRel32ToPtrJumpStubBypassable);
E.setTarget(getEntryForTarget(G, E.getTarget()));
return true;
}
return false;
}
Symbol &createEntry(LinkGraph &G, Symbol &Target) {
return createAnonymousPointerJumpStub(G, getStubsSection(G),
GOT.getEntryForTarget(G, Target));
}
public:
Section &getStubsSection(LinkGraph &G) {
if (!PLTSection)
PLTSection = &G.createSection(getSectionName(),
orc::MemProt::Read | orc::MemProt::Exec);
return *PLTSection;
}
GOTTableManager &GOT;
Section *PLTSection = nullptr;
};
/// Optimize the GOT and Stub relocations if the edge target address is in range
/// 1. PCRel32GOTLoadRelaxable. For this edge kind, if the target is in range,
/// then replace GOT load with lea. (THIS IS UNIMPLEMENTED RIGHT NOW!)
/// 2. BranchPCRel32ToPtrJumpStubRelaxable. For this edge kind, if the target is
/// in range, replace a indirect jump by plt stub with a direct jump to the
/// target
Error optimizeGOTAndStubAccesses(LinkGraph &G);
} // namespace llvm::jitlink::i386
#endif // LLVM_EXECUTIONENGINE_JITLINK_I386_H
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