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llvm-project/lld/COFF/Chunks.cpp

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//===- Chunks.cpp ---------------------------------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
#include "Chunks.h"
#include "COFFLinkerContext.h"
#include "InputFiles.h"
#include "SymbolTable.h"
#include "Symbols.h"
#include "Writer.h"
#include "lld/Common/ErrorHandler.h"
#include "llvm/ADT/Twine.h"
#include "llvm/BinaryFormat/COFF.h"
#include "llvm/Object/COFF.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
using namespace llvm;
using namespace llvm::object;
using namespace llvm::support::endian;
using namespace llvm::COFF;
using llvm::support::ulittle32_t;
namespace lld {
namespace coff {
SectionChunk::SectionChunk(ObjFile *f, const coff_section *h)
: Chunk(SectionKind), file(f), header(h), repl(this) {
// Initialize relocs.
if (file)
setRelocs(file->getCOFFObj()->getRelocations(header));
// Initialize sectionName.
StringRef sectionName;
if (file) {
if (Expected<StringRef> e = file->getCOFFObj()->getSectionName(header))
sectionName = *e;
}
sectionNameData = sectionName.data();
sectionNameSize = sectionName.size();
setAlignment(header->getAlignment());
hasData = !(header->Characteristics & IMAGE_SCN_CNT_UNINITIALIZED_DATA);
// If linker GC is disabled, every chunk starts out alive. If linker GC is
// enabled, treat non-comdat sections as roots. Generally optimized object
// files will be built with -ffunction-sections or /Gy, so most things worth
// stripping will be in a comdat.
if (config)
live = !config->doGC || !isCOMDAT();
else
live = true;
}
// SectionChunk is one of the most frequently allocated classes, so it is
// important to keep it as compact as possible. As of this writing, the number
// below is the size of this class on x64 platforms.
static_assert(sizeof(SectionChunk) <= 88, "SectionChunk grew unexpectedly");
static void add16(uint8_t *p, int16_t v) { write16le(p, read16le(p) + v); }
static void add32(uint8_t *p, int32_t v) { write32le(p, read32le(p) + v); }
static void add64(uint8_t *p, int64_t v) { write64le(p, read64le(p) + v); }
static void or16(uint8_t *p, uint16_t v) { write16le(p, read16le(p) | v); }
static void or32(uint8_t *p, uint32_t v) { write32le(p, read32le(p) | v); }
// Verify that given sections are appropriate targets for SECREL
// relocations. This check is relaxed because unfortunately debug
// sections have section-relative relocations against absolute symbols.
static bool checkSecRel(const SectionChunk *sec, OutputSection *os) {
if (os)
return true;
if (sec->isCodeView())
return false;
error("SECREL relocation cannot be applied to absolute symbols");
return false;
}
static void applySecRel(const SectionChunk *sec, uint8_t *off,
OutputSection *os, uint64_t s) {
if (!checkSecRel(sec, os))
return;
uint64_t secRel = s - os->getRVA();
if (secRel > UINT32_MAX) {
error("overflow in SECREL relocation in section: " + sec->getSectionName());
return;
}
add32(off, secRel);
}
static void applySecIdx(uint8_t *off, OutputSection *os) {
// Absolute symbol doesn't have section index, but section index relocation
// against absolute symbol should be resolved to one plus the last output
// section index. This is required for compatibility with MSVC.
if (os)
add16(off, os->sectionIndex);
else
add16(off, DefinedAbsolute::numOutputSections + 1);
}
void SectionChunk::applyRelX64(uint8_t *off, uint16_t type, OutputSection *os,
uint64_t s, uint64_t p) const {
switch (type) {
case IMAGE_REL_AMD64_ADDR32: add32(off, s + config->imageBase); break;
case IMAGE_REL_AMD64_ADDR64: add64(off, s + config->imageBase); break;
case IMAGE_REL_AMD64_ADDR32NB: add32(off, s); break;
case IMAGE_REL_AMD64_REL32: add32(off, s - p - 4); break;
case IMAGE_REL_AMD64_REL32_1: add32(off, s - p - 5); break;
case IMAGE_REL_AMD64_REL32_2: add32(off, s - p - 6); break;
case IMAGE_REL_AMD64_REL32_3: add32(off, s - p - 7); break;
case IMAGE_REL_AMD64_REL32_4: add32(off, s - p - 8); break;
case IMAGE_REL_AMD64_REL32_5: add32(off, s - p - 9); break;
case IMAGE_REL_AMD64_SECTION: applySecIdx(off, os); break;
case IMAGE_REL_AMD64_SECREL: applySecRel(this, off, os, s); break;
default:
error("unsupported relocation type 0x" + Twine::utohexstr(type) + " in " +
toString(file));
}
}
void SectionChunk::applyRelX86(uint8_t *off, uint16_t type, OutputSection *os,
uint64_t s, uint64_t p) const {
switch (type) {
case IMAGE_REL_I386_ABSOLUTE: break;
case IMAGE_REL_I386_DIR32: add32(off, s + config->imageBase); break;
case IMAGE_REL_I386_DIR32NB: add32(off, s); break;
case IMAGE_REL_I386_REL32: add32(off, s - p - 4); break;
case IMAGE_REL_I386_SECTION: applySecIdx(off, os); break;
case IMAGE_REL_I386_SECREL: applySecRel(this, off, os, s); break;
default:
error("unsupported relocation type 0x" + Twine::utohexstr(type) + " in " +
toString(file));
}
}
static void applyMOV(uint8_t *off, uint16_t v) {
write16le(off, (read16le(off) & 0xfbf0) | ((v & 0x800) >> 1) | ((v >> 12) & 0xf));
write16le(off + 2, (read16le(off + 2) & 0x8f00) | ((v & 0x700) << 4) | (v & 0xff));
}
static uint16_t readMOV(uint8_t *off, bool movt) {
uint16_t op1 = read16le(off);
if ((op1 & 0xfbf0) != (movt ? 0xf2c0 : 0xf240))
error("unexpected instruction in " + Twine(movt ? "MOVT" : "MOVW") +
" instruction in MOV32T relocation");
uint16_t op2 = read16le(off + 2);
if ((op2 & 0x8000) != 0)
error("unexpected instruction in " + Twine(movt ? "MOVT" : "MOVW") +
" instruction in MOV32T relocation");
return (op2 & 0x00ff) | ((op2 >> 4) & 0x0700) | ((op1 << 1) & 0x0800) |
((op1 & 0x000f) << 12);
}
void applyMOV32T(uint8_t *off, uint32_t v) {
uint16_t immW = readMOV(off, false); // read MOVW operand
uint16_t immT = readMOV(off + 4, true); // read MOVT operand
uint32_t imm = immW | (immT << 16);
v += imm; // add the immediate offset
applyMOV(off, v); // set MOVW operand
applyMOV(off + 4, v >> 16); // set MOVT operand
}
static void applyBranch20T(uint8_t *off, int32_t v) {
if (!isInt<21>(v))
error("relocation out of range");
uint32_t s = v < 0 ? 1 : 0;
uint32_t j1 = (v >> 19) & 1;
uint32_t j2 = (v >> 18) & 1;
or16(off, (s << 10) | ((v >> 12) & 0x3f));
or16(off + 2, (j1 << 13) | (j2 << 11) | ((v >> 1) & 0x7ff));
}
void applyBranch24T(uint8_t *off, int32_t v) {
if (!isInt<25>(v))
error("relocation out of range");
uint32_t s = v < 0 ? 1 : 0;
uint32_t j1 = ((~v >> 23) & 1) ^ s;
uint32_t j2 = ((~v >> 22) & 1) ^ s;
or16(off, (s << 10) | ((v >> 12) & 0x3ff));
// Clear out the J1 and J2 bits which may be set.
write16le(off + 2, (read16le(off + 2) & 0xd000) | (j1 << 13) | (j2 << 11) | ((v >> 1) & 0x7ff));
}
void SectionChunk::applyRelARM(uint8_t *off, uint16_t type, OutputSection *os,
uint64_t s, uint64_t p) const {
// Pointer to thumb code must have the LSB set.
uint64_t sx = s;
if (os && (os->header.Characteristics & IMAGE_SCN_MEM_EXECUTE))
sx |= 1;
switch (type) {
case IMAGE_REL_ARM_ADDR32: add32(off, sx + config->imageBase); break;
case IMAGE_REL_ARM_ADDR32NB: add32(off, sx); break;
case IMAGE_REL_ARM_MOV32T: applyMOV32T(off, sx + config->imageBase); break;
case IMAGE_REL_ARM_BRANCH20T: applyBranch20T(off, sx - p - 4); break;
case IMAGE_REL_ARM_BRANCH24T: applyBranch24T(off, sx - p - 4); break;
case IMAGE_REL_ARM_BLX23T: applyBranch24T(off, sx - p - 4); break;
case IMAGE_REL_ARM_SECTION: applySecIdx(off, os); break;
case IMAGE_REL_ARM_SECREL: applySecRel(this, off, os, s); break;
case IMAGE_REL_ARM_REL32: add32(off, sx - p - 4); break;
default:
error("unsupported relocation type 0x" + Twine::utohexstr(type) + " in " +
toString(file));
}
}
// Interpret the existing immediate value as a byte offset to the
// target symbol, then update the instruction with the immediate as
// the page offset from the current instruction to the target.
void applyArm64Addr(uint8_t *off, uint64_t s, uint64_t p, int shift) {
uint32_t orig = read32le(off);
int64_t imm =
SignExtend64<21>(((orig >> 29) & 0x3) | ((orig >> 3) & 0x1FFFFC));
s += imm;
imm = (s >> shift) - (p >> shift);
uint32_t immLo = (imm & 0x3) << 29;
uint32_t immHi = (imm & 0x1FFFFC) << 3;
uint64_t mask = (0x3 << 29) | (0x1FFFFC << 3);
write32le(off, (orig & ~mask) | immLo | immHi);
}
// Update the immediate field in a AARCH64 ldr, str, and add instruction.
// Optionally limit the range of the written immediate by one or more bits
// (rangeLimit).
void applyArm64Imm(uint8_t *off, uint64_t imm, uint32_t rangeLimit) {
uint32_t orig = read32le(off);
imm += (orig >> 10) & 0xFFF;
orig &= ~(0xFFF << 10);
write32le(off, orig | ((imm & (0xFFF >> rangeLimit)) << 10));
}
// Add the 12 bit page offset to the existing immediate.
// Ldr/str instructions store the opcode immediate scaled
// by the load/store size (giving a larger range for larger
// loads/stores). The immediate is always (both before and after
// fixing up the relocation) stored scaled similarly.
// Even if larger loads/stores have a larger range, limit the
// effective offset to 12 bit, since it is intended to be a
// page offset.
static void applyArm64Ldr(uint8_t *off, uint64_t imm) {
uint32_t orig = read32le(off);
uint32_t size = orig >> 30;
// 0x04000000 indicates SIMD/FP registers
// 0x00800000 indicates 128 bit
if ((orig & 0x4800000) == 0x4800000)
size += 4;
if ((imm & ((1 << size) - 1)) != 0)
error("misaligned ldr/str offset");
applyArm64Imm(off, imm >> size, size);
}
static void applySecRelLow12A(const SectionChunk *sec, uint8_t *off,
OutputSection *os, uint64_t s) {
if (checkSecRel(sec, os))
applyArm64Imm(off, (s - os->getRVA()) & 0xfff, 0);
}
static void applySecRelHigh12A(const SectionChunk *sec, uint8_t *off,
OutputSection *os, uint64_t s) {
if (!checkSecRel(sec, os))
return;
uint64_t secRel = (s - os->getRVA()) >> 12;
if (0xfff < secRel) {
error("overflow in SECREL_HIGH12A relocation in section: " +
sec->getSectionName());
return;
}
applyArm64Imm(off, secRel & 0xfff, 0);
}
static void applySecRelLdr(const SectionChunk *sec, uint8_t *off,
OutputSection *os, uint64_t s) {
if (checkSecRel(sec, os))
applyArm64Ldr(off, (s - os->getRVA()) & 0xfff);
}
void applyArm64Branch26(uint8_t *off, int64_t v) {
if (!isInt<28>(v))
error("relocation out of range");
or32(off, (v & 0x0FFFFFFC) >> 2);
}
static void applyArm64Branch19(uint8_t *off, int64_t v) {
if (!isInt<21>(v))
error("relocation out of range");
or32(off, (v & 0x001FFFFC) << 3);
}
static void applyArm64Branch14(uint8_t *off, int64_t v) {
if (!isInt<16>(v))
error("relocation out of range");
or32(off, (v & 0x0000FFFC) << 3);
}
void SectionChunk::applyRelARM64(uint8_t *off, uint16_t type, OutputSection *os,
uint64_t s, uint64_t p) const {
switch (type) {
case IMAGE_REL_ARM64_PAGEBASE_REL21: applyArm64Addr(off, s, p, 12); break;
case IMAGE_REL_ARM64_REL21: applyArm64Addr(off, s, p, 0); break;
case IMAGE_REL_ARM64_PAGEOFFSET_12A: applyArm64Imm(off, s & 0xfff, 0); break;
case IMAGE_REL_ARM64_PAGEOFFSET_12L: applyArm64Ldr(off, s & 0xfff); break;
case IMAGE_REL_ARM64_BRANCH26: applyArm64Branch26(off, s - p); break;
case IMAGE_REL_ARM64_BRANCH19: applyArm64Branch19(off, s - p); break;
case IMAGE_REL_ARM64_BRANCH14: applyArm64Branch14(off, s - p); break;
case IMAGE_REL_ARM64_ADDR32: add32(off, s + config->imageBase); break;
case IMAGE_REL_ARM64_ADDR32NB: add32(off, s); break;
case IMAGE_REL_ARM64_ADDR64: add64(off, s + config->imageBase); break;
case IMAGE_REL_ARM64_SECREL: applySecRel(this, off, os, s); break;
case IMAGE_REL_ARM64_SECREL_LOW12A: applySecRelLow12A(this, off, os, s); break;
case IMAGE_REL_ARM64_SECREL_HIGH12A: applySecRelHigh12A(this, off, os, s); break;
case IMAGE_REL_ARM64_SECREL_LOW12L: applySecRelLdr(this, off, os, s); break;
case IMAGE_REL_ARM64_SECTION: applySecIdx(off, os); break;
case IMAGE_REL_ARM64_REL32: add32(off, s - p - 4); break;
default:
error("unsupported relocation type 0x" + Twine::utohexstr(type) + " in " +
toString(file));
}
}
static void maybeReportRelocationToDiscarded(const SectionChunk *fromChunk,
Defined *sym,
const coff_relocation &rel) {
// Don't report these errors when the relocation comes from a debug info
// section or in mingw mode. MinGW mode object files (built by GCC) can
// have leftover sections with relocations against discarded comdat
// sections. Such sections are left as is, with relocations untouched.
if (fromChunk->isCodeView() || fromChunk->isDWARF() || config->mingw)
return;
// Get the name of the symbol. If it's null, it was discarded early, so we
// have to go back to the object file.
ObjFile *file = fromChunk->file;
StringRef name;
if (sym) {
name = sym->getName();
} else {
COFFSymbolRef coffSym =
check(file->getCOFFObj()->getSymbol(rel.SymbolTableIndex));
name = check(file->getCOFFObj()->getSymbolName(coffSym));
}
std::vector<std::string> symbolLocations =
getSymbolLocations(file, rel.SymbolTableIndex);
std::string out;
llvm::raw_string_ostream os(out);
os << "relocation against symbol in discarded section: " + name;
for (const std::string &s : symbolLocations)
os << s;
error(os.str());
}
void SectionChunk::writeTo(uint8_t *buf) const {
if (!hasData)
return;
// Copy section contents from source object file to output file.
ArrayRef<uint8_t> a = getContents();
if (!a.empty())
memcpy(buf, a.data(), a.size());
// Apply relocations.
size_t inputSize = getSize();
for (const coff_relocation &rel : getRelocs()) {
// Check for an invalid relocation offset. This check isn't perfect, because
// we don't have the relocation size, which is only known after checking the
// machine and relocation type. As a result, a relocation may overwrite the
// beginning of the following input section.
if (rel.VirtualAddress >= inputSize) {
error("relocation points beyond the end of its parent section");
continue;
}
applyRelocation(buf + rel.VirtualAddress, rel);
}
}
void SectionChunk::applyRelocation(uint8_t *off,
const coff_relocation &rel) const {
auto *sym = dyn_cast_or_null<Defined>(file->getSymbol(rel.SymbolTableIndex));
// Get the output section of the symbol for this relocation. The output
// section is needed to compute SECREL and SECTION relocations used in debug
// info.
Chunk *c = sym ? sym->getChunk() : nullptr;
OutputSection *os = c ? file->ctx.getOutputSection(c) : nullptr;
// Skip the relocation if it refers to a discarded section, and diagnose it
// as an error if appropriate. If a symbol was discarded early, it may be
// null. If it was discarded late, the output section will be null, unless
// it was an absolute or synthetic symbol.
if (!sym ||
(!os && !isa<DefinedAbsolute>(sym) && !isa<DefinedSynthetic>(sym))) {
maybeReportRelocationToDiscarded(this, sym, rel);
return;
}
uint64_t s = sym->getRVA();
// Compute the RVA of the relocation for relative relocations.
uint64_t p = rva + rel.VirtualAddress;
switch (config->machine) {
case AMD64:
applyRelX64(off, rel.Type, os, s, p);
break;
case I386:
applyRelX86(off, rel.Type, os, s, p);
break;
case ARMNT:
applyRelARM(off, rel.Type, os, s, p);
break;
case ARM64:
applyRelARM64(off, rel.Type, os, s, p);
break;
default:
llvm_unreachable("unknown machine type");
}
}
// Defend against unsorted relocations. This may be overly conservative.
void SectionChunk::sortRelocations() {
auto cmpByVa = [](const coff_relocation &l, const coff_relocation &r) {
return l.VirtualAddress < r.VirtualAddress;
};
if (llvm::is_sorted(getRelocs(), cmpByVa))
return;
warn("some relocations in " + file->getName() + " are not sorted");
MutableArrayRef<coff_relocation> newRelocs(
bAlloc.Allocate<coff_relocation>(relocsSize), relocsSize);
memcpy(newRelocs.data(), relocsData, relocsSize * sizeof(coff_relocation));
llvm::sort(newRelocs, cmpByVa);
setRelocs(newRelocs);
}
// Similar to writeTo, but suitable for relocating a subsection of the overall
// section.
void SectionChunk::writeAndRelocateSubsection(ArrayRef<uint8_t> sec,
ArrayRef<uint8_t> subsec,
uint32_t &nextRelocIndex,
uint8_t *buf) const {
assert(!subsec.empty() && !sec.empty());
assert(sec.begin() <= subsec.begin() && subsec.end() <= sec.end() &&
"subsection is not part of this section");
size_t vaBegin = std::distance(sec.begin(), subsec.begin());
size_t vaEnd = std::distance(sec.begin(), subsec.end());
memcpy(buf, subsec.data(), subsec.size());
for (; nextRelocIndex < relocsSize; ++nextRelocIndex) {
const coff_relocation &rel = relocsData[nextRelocIndex];
// Only apply relocations that apply to this subsection. These checks
// assume that all subsections completely contain their relocations.
// Relocations must not straddle the beginning or end of a subsection.
if (rel.VirtualAddress < vaBegin)
continue;
if (rel.VirtualAddress + 1 >= vaEnd)
break;
applyRelocation(&buf[rel.VirtualAddress - vaBegin], rel);
}
}
void SectionChunk::addAssociative(SectionChunk *child) {
// Insert the child section into the list of associated children. Keep the
// list ordered by section name so that ICF does not depend on section order.
assert(child->assocChildren == nullptr &&
"associated sections cannot have their own associated children");
SectionChunk *prev = this;
SectionChunk *next = assocChildren;
for (; next != nullptr; prev = next, next = next->assocChildren) {
if (next->getSectionName() <= child->getSectionName())
break;
}
// Insert child between prev and next.
assert(prev->assocChildren == next);
prev->assocChildren = child;
child->assocChildren = next;
}
static uint8_t getBaserelType(const coff_relocation &rel) {
switch (config->machine) {
case AMD64:
if (rel.Type == IMAGE_REL_AMD64_ADDR64)
return IMAGE_REL_BASED_DIR64;
if (rel.Type == IMAGE_REL_AMD64_ADDR32)
return IMAGE_REL_BASED_HIGHLOW;
return IMAGE_REL_BASED_ABSOLUTE;
case I386:
if (rel.Type == IMAGE_REL_I386_DIR32)
return IMAGE_REL_BASED_HIGHLOW;
return IMAGE_REL_BASED_ABSOLUTE;
case ARMNT:
if (rel.Type == IMAGE_REL_ARM_ADDR32)
return IMAGE_REL_BASED_HIGHLOW;
if (rel.Type == IMAGE_REL_ARM_MOV32T)
return IMAGE_REL_BASED_ARM_MOV32T;
return IMAGE_REL_BASED_ABSOLUTE;
case ARM64:
if (rel.Type == IMAGE_REL_ARM64_ADDR64)
return IMAGE_REL_BASED_DIR64;
return IMAGE_REL_BASED_ABSOLUTE;
default:
llvm_unreachable("unknown machine type");
}
}
// Windows-specific.
// Collect all locations that contain absolute addresses, which need to be
// fixed by the loader if load-time relocation is needed.
// Only called when base relocation is enabled.
void SectionChunk::getBaserels(std::vector<Baserel> *res) {
for (const coff_relocation &rel : getRelocs()) {
uint8_t ty = getBaserelType(rel);
if (ty == IMAGE_REL_BASED_ABSOLUTE)
continue;
Symbol *target = file->getSymbol(rel.SymbolTableIndex);
if (!target || isa<DefinedAbsolute>(target))
continue;
res->emplace_back(rva + rel.VirtualAddress, ty);
}
}
// MinGW specific.
// Check whether a static relocation of type Type can be deferred and
// handled at runtime as a pseudo relocation (for references to a module
// local variable, which turned out to actually need to be imported from
// another DLL) This returns the size the relocation is supposed to update,
// in bits, or 0 if the relocation cannot be handled as a runtime pseudo
// relocation.
static int getRuntimePseudoRelocSize(uint16_t type) {
// Relocations that either contain an absolute address, or a plain
// relative offset, since the runtime pseudo reloc implementation
// adds 8/16/32/64 bit values to a memory address.
//
// Given a pseudo relocation entry,
//
// typedef struct {
// DWORD sym;
// DWORD target;
// DWORD flags;
// } runtime_pseudo_reloc_item_v2;
//
// the runtime relocation performs this adjustment:
// *(base + .target) += *(base + .sym) - (base + .sym)
//
// This works for both absolute addresses (IMAGE_REL_*_ADDR32/64,
// IMAGE_REL_I386_DIR32, where the memory location initially contains
// the address of the IAT slot, and for relative addresses (IMAGE_REL*_REL32),
// where the memory location originally contains the relative offset to the
// IAT slot.
//
// This requires the target address to be writable, either directly out of
// the image, or temporarily changed at runtime with VirtualProtect.
// Since this only operates on direct address values, it doesn't work for
// ARM/ARM64 relocations, other than the plain ADDR32/ADDR64 relocations.
switch (config->machine) {
case AMD64:
switch (type) {
case IMAGE_REL_AMD64_ADDR64:
return 64;
case IMAGE_REL_AMD64_ADDR32:
case IMAGE_REL_AMD64_REL32:
case IMAGE_REL_AMD64_REL32_1:
case IMAGE_REL_AMD64_REL32_2:
case IMAGE_REL_AMD64_REL32_3:
case IMAGE_REL_AMD64_REL32_4:
case IMAGE_REL_AMD64_REL32_5:
return 32;
default:
return 0;
}
case I386:
switch (type) {
case IMAGE_REL_I386_DIR32:
case IMAGE_REL_I386_REL32:
return 32;
default:
return 0;
}
case ARMNT:
switch (type) {
case IMAGE_REL_ARM_ADDR32:
return 32;
default:
return 0;
}
case ARM64:
switch (type) {
case IMAGE_REL_ARM64_ADDR64:
return 64;
case IMAGE_REL_ARM64_ADDR32:
return 32;
default:
return 0;
}
default:
llvm_unreachable("unknown machine type");
}
}
// MinGW specific.
// Append information to the provided vector about all relocations that
// need to be handled at runtime as runtime pseudo relocations (references
// to a module local variable, which turned out to actually need to be
// imported from another DLL).
void SectionChunk::getRuntimePseudoRelocs(
std::vector<RuntimePseudoReloc> &res) {
for (const coff_relocation &rel : getRelocs()) {
auto *target =
dyn_cast_or_null<Defined>(file->getSymbol(rel.SymbolTableIndex));
if (!target || !target->isRuntimePseudoReloc)
continue;
int sizeInBits = getRuntimePseudoRelocSize(rel.Type);
if (sizeInBits == 0) {
error("unable to automatically import from " + target->getName() +
" with relocation type " +
file->getCOFFObj()->getRelocationTypeName(rel.Type) + " in " +
toString(file));
continue;
}
// sizeInBits is used to initialize the Flags field; currently no
// other flags are defined.
res.emplace_back(
RuntimePseudoReloc(target, this, rel.VirtualAddress, sizeInBits));
}
}
bool SectionChunk::isCOMDAT() const {
return header->Characteristics & IMAGE_SCN_LNK_COMDAT;
}
void SectionChunk::printDiscardedMessage() const {
// Removed by dead-stripping. If it's removed by ICF, ICF already
// printed out the name, so don't repeat that here.
if (sym && this == repl)
message("Discarded " + sym->getName());
}
StringRef SectionChunk::getDebugName() const {
if (sym)
return sym->getName();
return "";
}
ArrayRef<uint8_t> SectionChunk::getContents() const {
ArrayRef<uint8_t> a;
cantFail(file->getCOFFObj()->getSectionContents(header, a));
return a;
}
ArrayRef<uint8_t> SectionChunk::consumeDebugMagic() {
assert(isCodeView());
return consumeDebugMagic(getContents(), getSectionName());
}
ArrayRef<uint8_t> SectionChunk::consumeDebugMagic(ArrayRef<uint8_t> data,
StringRef sectionName) {
if (data.empty())
return {};
// First 4 bytes are section magic.
if (data.size() < 4)
fatal("the section is too short: " + sectionName);
if (!sectionName.startswith(".debug$"))
fatal("invalid section: " + sectionName);
uint32_t magic = support::endian::read32le(data.data());
uint32_t expectedMagic = sectionName == ".debug$H"
? DEBUG_HASHES_SECTION_MAGIC
: DEBUG_SECTION_MAGIC;
if (magic != expectedMagic) {
warn("ignoring section " + sectionName + " with unrecognized magic 0x" +
utohexstr(magic));
return {};
}
return data.slice(4);
}
SectionChunk *SectionChunk::findByName(ArrayRef<SectionChunk *> sections,
StringRef name) {
for (SectionChunk *c : sections)
if (c->getSectionName() == name)
return c;
return nullptr;
}
void SectionChunk::replace(SectionChunk *other) {
p2Align = std::max(p2Align, other->p2Align);
other->repl = repl;
other->live = false;
}
uint32_t SectionChunk::getSectionNumber() const {
DataRefImpl r;
r.p = reinterpret_cast<uintptr_t>(header);
SectionRef s(r, file->getCOFFObj());
return s.getIndex() + 1;
}
CommonChunk::CommonChunk(const COFFSymbolRef s) : sym(s) {
// The value of a common symbol is its size. Align all common symbols smaller
// than 32 bytes naturally, i.e. round the size up to the next power of two.
// This is what MSVC link.exe does.
setAlignment(std::min(32U, uint32_t(PowerOf2Ceil(sym.getValue()))));
hasData = false;
}
uint32_t CommonChunk::getOutputCharacteristics() const {
return IMAGE_SCN_CNT_UNINITIALIZED_DATA | IMAGE_SCN_MEM_READ |
IMAGE_SCN_MEM_WRITE;
}
void StringChunk::writeTo(uint8_t *buf) const {
memcpy(buf, str.data(), str.size());
buf[str.size()] = '\0';
}
ImportThunkChunkX64::ImportThunkChunkX64(Defined *s) : ImportThunkChunk(s) {
// Intel Optimization Manual says that all branch targets
// should be 16-byte aligned. MSVC linker does this too.
setAlignment(16);
}
void ImportThunkChunkX64::writeTo(uint8_t *buf) const {
memcpy(buf, importThunkX86, sizeof(importThunkX86));
// The first two bytes is a JMP instruction. Fill its operand.
write32le(buf + 2, impSymbol->getRVA() - rva - getSize());
}
void ImportThunkChunkX86::getBaserels(std::vector<Baserel> *res) {
res->emplace_back(getRVA() + 2);
}
void ImportThunkChunkX86::writeTo(uint8_t *buf) const {
memcpy(buf, importThunkX86, sizeof(importThunkX86));
// The first two bytes is a JMP instruction. Fill its operand.
write32le(buf + 2,
impSymbol->getRVA() + config->imageBase);
}
void ImportThunkChunkARM::getBaserels(std::vector<Baserel> *res) {
res->emplace_back(getRVA(), IMAGE_REL_BASED_ARM_MOV32T);
}
void ImportThunkChunkARM::writeTo(uint8_t *buf) const {
memcpy(buf, importThunkARM, sizeof(importThunkARM));
// Fix mov.w and mov.t operands.
applyMOV32T(buf, impSymbol->getRVA() + config->imageBase);
}
void ImportThunkChunkARM64::writeTo(uint8_t *buf) const {
int64_t off = impSymbol->getRVA() & 0xfff;
memcpy(buf, importThunkARM64, sizeof(importThunkARM64));
applyArm64Addr(buf, impSymbol->getRVA(), rva, 12);
applyArm64Ldr(buf + 4, off);
}
// A Thumb2, PIC, non-interworking range extension thunk.
const uint8_t armThunk[] = {
0x40, 0xf2, 0x00, 0x0c, // P: movw ip,:lower16:S - (P + (L1-P) + 4)
0xc0, 0xf2, 0x00, 0x0c, // movt ip,:upper16:S - (P + (L1-P) + 4)
0xe7, 0x44, // L1: add pc, ip
};
size_t RangeExtensionThunkARM::getSize() const {
assert(config->machine == ARMNT);
return sizeof(armThunk);
}
void RangeExtensionThunkARM::writeTo(uint8_t *buf) const {
assert(config->machine == ARMNT);
uint64_t offset = target->getRVA() - rva - 12;
memcpy(buf, armThunk, sizeof(armThunk));
applyMOV32T(buf, uint32_t(offset));
}
// A position independent ARM64 adrp+add thunk, with a maximum range of
// +/- 4 GB, which is enough for any PE-COFF.
const uint8_t arm64Thunk[] = {
0x10, 0x00, 0x00, 0x90, // adrp x16, Dest
0x10, 0x02, 0x00, 0x91, // add x16, x16, :lo12:Dest
0x00, 0x02, 0x1f, 0xd6, // br x16
};
size_t RangeExtensionThunkARM64::getSize() const {
assert(config->machine == ARM64);
return sizeof(arm64Thunk);
}
void RangeExtensionThunkARM64::writeTo(uint8_t *buf) const {
assert(config->machine == ARM64);
memcpy(buf, arm64Thunk, sizeof(arm64Thunk));
applyArm64Addr(buf + 0, target->getRVA(), rva, 12);
applyArm64Imm(buf + 4, target->getRVA() & 0xfff, 0);
}
void LocalImportChunk::getBaserels(std::vector<Baserel> *res) {
res->emplace_back(getRVA());
}
size_t LocalImportChunk::getSize() const { return config->wordsize; }
void LocalImportChunk::writeTo(uint8_t *buf) const {
if (config->is64()) {
write64le(buf, sym->getRVA() + config->imageBase);
} else {
write32le(buf, sym->getRVA() + config->imageBase);
}
}
void RVATableChunk::writeTo(uint8_t *buf) const {
ulittle32_t *begin = reinterpret_cast<ulittle32_t *>(buf);
size_t cnt = 0;
for (const ChunkAndOffset &co : syms)
begin[cnt++] = co.inputChunk->getRVA() + co.offset;
std::sort(begin, begin + cnt);
assert(std::unique(begin, begin + cnt) == begin + cnt &&
"RVA tables should be de-duplicated");
}
void RVAFlagTableChunk::writeTo(uint8_t *buf) const {
struct RVAFlag {
ulittle32_t rva;
uint8_t flag;
};
auto flags =
makeMutableArrayRef(reinterpret_cast<RVAFlag *>(buf), syms.size());
for (auto t : zip(syms, flags)) {
const auto &sym = std::get<0>(t);
auto &flag = std::get<1>(t);
flag.rva = sym.inputChunk->getRVA() + sym.offset;
flag.flag = 0;
}
llvm::sort(flags,
[](const RVAFlag &a, const RVAFlag &b) { return a.rva < b.rva; });
assert(llvm::unique(flags, [](const RVAFlag &a,
const RVAFlag &b) { return a.rva == b.rva; }) ==
flags.end() &&
"RVA tables should be de-duplicated");
}
// MinGW specific, for the "automatic import of variables from DLLs" feature.
size_t PseudoRelocTableChunk::getSize() const {
if (relocs.empty())
return 0;
return 12 + 12 * relocs.size();
}
// MinGW specific.
void PseudoRelocTableChunk::writeTo(uint8_t *buf) const {
if (relocs.empty())
return;
ulittle32_t *table = reinterpret_cast<ulittle32_t *>(buf);
// This is the list header, to signal the runtime pseudo relocation v2
// format.
table[0] = 0;
table[1] = 0;
table[2] = 1;
size_t idx = 3;
for (const RuntimePseudoReloc &rpr : relocs) {
table[idx + 0] = rpr.sym->getRVA();
table[idx + 1] = rpr.target->getRVA() + rpr.targetOffset;
table[idx + 2] = rpr.flags;
idx += 3;
}
}
// Windows-specific. This class represents a block in .reloc section.
// The format is described here.
//
// On Windows, each DLL is linked against a fixed base address and
// usually loaded to that address. However, if there's already another
// DLL that overlaps, the loader has to relocate it. To do that, DLLs
// contain .reloc sections which contain offsets that need to be fixed
// up at runtime. If the loader finds that a DLL cannot be loaded to its
// desired base address, it loads it to somewhere else, and add <actual
// base address> - <desired base address> to each offset that is
// specified by the .reloc section. In ELF terms, .reloc sections
// contain relative relocations in REL format (as opposed to RELA.)
//
// This already significantly reduces the size of relocations compared
// to ELF .rel.dyn, but Windows does more to reduce it (probably because
// it was invented for PCs in the late '80s or early '90s.) Offsets in
// .reloc are grouped by page where the page size is 12 bits, and
// offsets sharing the same page address are stored consecutively to
// represent them with less space. This is very similar to the page
// table which is grouped by (multiple stages of) pages.
//
// For example, let's say we have 0x00030, 0x00500, 0x00700, 0x00A00,
// 0x20004, and 0x20008 in a .reloc section for x64. The uppermost 4
// bits have a type IMAGE_REL_BASED_DIR64 or 0xA. In the section, they
// are represented like this:
//
// 0x00000 -- page address (4 bytes)
// 16 -- size of this block (4 bytes)
// 0xA030 -- entries (2 bytes each)
// 0xA500
// 0xA700
// 0xAA00
// 0x20000 -- page address (4 bytes)
// 12 -- size of this block (4 bytes)
// 0xA004 -- entries (2 bytes each)
// 0xA008
//
// Usually we have a lot of relocations for each page, so the number of
// bytes for one .reloc entry is close to 2 bytes on average.
BaserelChunk::BaserelChunk(uint32_t page, Baserel *begin, Baserel *end) {
// Block header consists of 4 byte page RVA and 4 byte block size.
// Each entry is 2 byte. Last entry may be padding.
data.resize(alignTo((end - begin) * 2 + 8, 4));
uint8_t *p = data.data();
write32le(p, page);
write32le(p + 4, data.size());
p += 8;
for (Baserel *i = begin; i != end; ++i) {
write16le(p, (i->type << 12) | (i->rva - page));
p += 2;
}
}
void BaserelChunk::writeTo(uint8_t *buf) const {
memcpy(buf, data.data(), data.size());
}
uint8_t Baserel::getDefaultType() {
switch (config->machine) {
case AMD64:
case ARM64:
return IMAGE_REL_BASED_DIR64;
case I386:
case ARMNT:
return IMAGE_REL_BASED_HIGHLOW;
default:
llvm_unreachable("unknown machine type");
}
}
MergeChunk::MergeChunk(uint32_t alignment)
: builder(StringTableBuilder::RAW, alignment) {
setAlignment(alignment);
}
void MergeChunk::addSection(COFFLinkerContext &ctx, SectionChunk *c) {
assert(isPowerOf2_32(c->getAlignment()));
uint8_t p2Align = llvm::Log2_32(c->getAlignment());
assert(p2Align < array_lengthof(ctx.mergeChunkInstances));
auto *&mc = ctx.mergeChunkInstances[p2Align];
if (!mc)
mc = make<MergeChunk>(c->getAlignment());
mc->sections.push_back(c);
}
void MergeChunk::finalizeContents() {
assert(!finalized && "should only finalize once");
for (SectionChunk *c : sections)
if (c->live)
builder.add(toStringRef(c->getContents()));
builder.finalize();
finalized = true;
}
void MergeChunk::assignSubsectionRVAs() {
for (SectionChunk *c : sections) {
if (!c->live)
continue;
size_t off = builder.getOffset(toStringRef(c->getContents()));
c->setRVA(rva + off);
}
}
uint32_t MergeChunk::getOutputCharacteristics() const {
return IMAGE_SCN_MEM_READ | IMAGE_SCN_CNT_INITIALIZED_DATA;
}
size_t MergeChunk::getSize() const {
return builder.getSize();
}
void MergeChunk::writeTo(uint8_t *buf) const {
builder.write(buf);
}
// MinGW specific.
size_t AbsolutePointerChunk::getSize() const { return config->wordsize; }
void AbsolutePointerChunk::writeTo(uint8_t *buf) const {
if (config->is64()) {
write64le(buf, value);
} else {
write32le(buf, value);
}
}
} // namespace coff
} // namespace lld
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