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Revert "[lld-macho] Support .subsections_via_symbols" 

Due to build breakage mentioned in https://reviews.llvm.org/D79926.

This reverts commit e270b2f172.
This commit is contained in:
Jez Ng 2020-05-19 08:29:17 -07:00
parent db8559eee4
commit 70fbbcdd34
7 changed files with 80 additions and 278 deletions
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11
lld/MachO/Driver.cpp
View File

@ -326,14 +326,9 @@ bool macho::link(llvm::ArrayRef<const char *> argsArr, bool canExitEarly,
createSyntheticSections();
// Initialize InputSections.
for (InputFile *file : inputFiles) {
for (SubsectionMap &map : file->subsections) {
for (auto &p : map) {
InputSection *isec = p.second;
inputSections.push_back(isec);
}
}
}
for (InputFile *file : inputFiles)
for (InputSection *sec : file->sections)
inputSections.push_back(sec);
// Write to an output file.
writeResult();

212
lld/MachO/InputFiles.cpp
View File

@ -127,13 +127,17 @@ static const load_command *findCommand(const mach_header_64 *hdr,
return nullptr;
}
void InputFile::parseSections(ArrayRef<section_64> sections) {
subsections.reserve(sections.size());
std::vector<InputSection *>
InputFile::parseSections(ArrayRef<section_64> sections) {
std::vector<InputSection *> ret;
ret.reserve(sections.size());
auto *buf = reinterpret_cast<const uint8_t *>(mb.getBufferStart());
for (const section_64 &sec : sections) {
InputSection *isec = make<InputSection>();
isec->file = this;
isec->header = &sec;
isec->name = StringRef(sec.sectname, strnlen(sec.sectname, 16));
isec->segname = StringRef(sec.segname, strnlen(sec.segname, 16));
isec->data = {buf + sec.offset, static_cast<size_t>(sec.size)};
@ -143,185 +147,96 @@ void InputFile::parseSections(ArrayRef<section_64> sections) {
else
isec->align = 1 << sec.align;
isec->flags = sec.flags;
subsections.push_back({{0, isec}});
ret.push_back(isec);
}
}
// Find the subsection corresponding to the greatest section offset that is <=
// that of the given offset.
//
// offset: an offset relative to the start of the original InputSection (before
// any subsection splitting has occurred). It will be updated to represent the
// same location as an offset relative to the start of the containing
// subsection.
static InputSection *findContainingSubsection(SubsectionMap &map,
uint32_t *offset) {
auto it = std::prev(map.upper_bound(*offset));
*offset -= it->first;
return it->second;
return ret;
}
void InputFile::parseRelocations(const section_64 &sec,
SubsectionMap &subsecMap) {
std::vector<Reloc> &relocs) {
auto *buf = reinterpret_cast<const uint8_t *>(mb.getBufferStart());
ArrayRef<any_relocation_info> relInfos(
reinterpret_cast<const any_relocation_info *>(buf + sec.reloff),
sec.nreloc);
for (const any_relocation_info &anyRel : relInfos) {
if (anyRel.r_word0 & R_SCATTERED)
fatal("TODO: Scattered relocations not supported");
auto rel = reinterpret_cast<const relocation_info &>(anyRel);
if (!rel.r_pcrel)
fatal("TODO: Only pcrel relocations are supported");
Reloc r;
r.type = rel.r_type;
uint32_t secRelOffset = rel.r_address;
uint64_t rawAddend =
target->getImplicitAddend(buf + sec.offset + secRelOffset, r.type);
if (rel.r_extern) {
r.target = symbols[rel.r_symbolnum];
r.addend = rawAddend;
if (anyRel.r_word0 & R_SCATTERED) {
error("TODO: Scattered relocations not supported");
} else {
if (rel.r_symbolnum == 0 || rel.r_symbolnum > subsections.size())
fatal("invalid section index in relocation for offset " +
std::to_string(r.offset) + " in section " + sec.sectname +
" of " + getName());
SubsectionMap &targetSubsecMap = subsections[rel.r_symbolnum - 1];
const section_64 &targetSec = sectionHeaders[rel.r_symbolnum - 1];
// The implicit addend for pcrel section relocations is the pcrel offset
// in terms of the addresses in the input file. Here we adjust it so that
// it describes the offset from the start of the target section.
// TODO: Figure out what to do for non-pcrel section relocations.
// TODO: The offset of 4 is probably not right for ARM64, nor for
// relocations with r_length != 2.
uint32_t targetOffset =
sec.addr + secRelOffset + 4 + rawAddend - targetSec.addr;
r.target = findContainingSubsection(targetSubsecMap, &targetOffset);
r.addend = targetOffset;
auto rel = reinterpret_cast<const relocation_info &>(anyRel);
r.type = rel.r_type;
r.offset = rel.r_address;
r.addend = target->getImplicitAddend(buf + sec.offset + r.offset, r.type);
if (rel.r_extern) {
r.target = symbols[rel.r_symbolnum];
} else {
if (rel.r_symbolnum == 0 || rel.r_symbolnum > sections.size())
fatal("invalid section index in relocation for offset " +
std::to_string(r.offset) + " in section " + sec.sectname +
" of " + getName());
r.target = sections[rel.r_symbolnum - 1];
}
}
InputSection *subsec = findContainingSubsection(subsecMap, &secRelOffset);
r.offset = secRelOffset;
subsec->relocs.push_back(r);
}
}
void InputFile::parseSymbols(ArrayRef<const nlist_64> nList, const char *strtab,
bool subsectionsViaSymbols) {
// resize(), not reserve(), because we are going to create N_ALT_ENTRY symbols
// out-of-sequence.
symbols.resize(nList.size());
std::vector<size_t> altEntrySymIdxs;
auto createDefined = [&](const nlist_64 &sym, InputSection *isec,
uint32_t value) -> Symbol * {
StringRef name = strtab + sym.n_strx;
if (sym.n_type & N_EXT)
// Global defined symbol
return symtab->addDefined(name, isec, value);
else
// Local defined symbol
return make<Defined>(name, isec, value);
};
for (size_t i = 0, n = nList.size(); i < n; ++i) {
const nlist_64 &sym = nList[i];
// Undefined symbol
if (!sym.n_sect) {
StringRef name = strtab + sym.n_strx;
symbols[i] = symtab->addUndefined(name);
continue;
}
const section_64 &sec = sectionHeaders[sym.n_sect - 1];
SubsectionMap &subsecMap = subsections[sym.n_sect - 1];
uint64_t offset = sym.n_value - sec.addr;
// If the input file does not use subsections-via-symbols, all symbols can
// use the same subsection. Otherwise, we must split the sections along
// symbol boundaries.
if (!subsectionsViaSymbols) {
symbols[i] = createDefined(sym, subsecMap[0], offset);
continue;
}
// nList entries aren't necessarily arranged in address order. Therefore,
// we can't create alt-entry symbols at this point because a later symbol
// may split its section, which may affect which subsection the alt-entry
// symbol is assigned to. So we need to handle them in a second pass below.
if (sym.n_desc & N_ALT_ENTRY) {
altEntrySymIdxs.push_back(i);
continue;
}
// Find the subsection corresponding to the greatest section offset that is
// <= that of the current symbol. The subsection that we find either needs
// to be used directly or split in two.
uint32_t firstSize = offset;
InputSection *firstIsec = findContainingSubsection(subsecMap, &firstSize);
if (firstSize == 0) {
// Alias of an existing symbol, or the first symbol in the section. These
// are handled by reusing the existing section.
symbols[i] = createDefined(sym, firstIsec, 0);
continue;
}
// We saw a symbol definition at a new offset. Split the section into two
// subsections. The new symbol uses the second subsection.
auto *secondIsec = make<InputSection>(*firstIsec);
secondIsec->data = firstIsec->data.slice(firstSize);
firstIsec->data = firstIsec->data.slice(0, firstSize);
// TODO: ld64 appears to preserve the original alignment as well as each
// subsection's offset from the last aligned address. We should consider
// emulating that behavior.
secondIsec->align = MinAlign(firstIsec->align, offset);
subsecMap[offset] = secondIsec;
// By construction, the symbol will be at offset zero in the new section.
symbols[i] = createDefined(sym, secondIsec, 0);
}
for (size_t idx : altEntrySymIdxs) {
const nlist_64 &sym = nList[idx];
SubsectionMap &subsecMap = subsections[sym.n_sect - 1];
uint32_t off = sym.n_value - sectionHeaders[sym.n_sect - 1].addr;
InputSection *subsec = findContainingSubsection(subsecMap, &off);
symbols[idx] = createDefined(sym, subsec, off);
relocs.push_back(r);
}
}
ObjFile::ObjFile(MemoryBufferRef mb) : InputFile(ObjKind, mb) {
auto *buf = reinterpret_cast<const uint8_t *>(mb.getBufferStart());
auto *hdr = reinterpret_cast<const mach_header_64 *>(mb.getBufferStart());
ArrayRef<section_64> objSections;
if (const load_command *cmd = findCommand(hdr, LC_SEGMENT_64)) {
auto *c = reinterpret_cast<const segment_command_64 *>(cmd);
sectionHeaders = ArrayRef<section_64>{
objSections = ArrayRef<section_64>{
reinterpret_cast<const section_64 *>(c + 1), c->nsects};
parseSections(sectionHeaders);
sections = parseSections(objSections);
}
// TODO: Error on missing LC_SYMTAB?
if (const load_command *cmd = findCommand(hdr, LC_SYMTAB)) {
auto *c = reinterpret_cast<const symtab_command *>(cmd);
const char *strtab = reinterpret_cast<const char *>(buf) + c->stroff;
ArrayRef<const nlist_64> nList(
reinterpret_cast<const nlist_64 *>(buf + c->symoff), c->nsyms);
const char *strtab = reinterpret_cast<const char *>(buf) + c->stroff;
bool subsectionsViaSymbols = hdr->flags & MH_SUBSECTIONS_VIA_SYMBOLS;
parseSymbols(nList, strtab, subsectionsViaSymbols);
symbols.reserve(c->nsyms);
for (const nlist_64 &sym : nList) {
StringRef name = strtab + sym.n_strx;
// Undefined symbol
if (!sym.n_sect) {
symbols.push_back(symtab->addUndefined(name));
continue;
}
InputSection *isec = sections[sym.n_sect - 1];
const section_64 &objSec = objSections[sym.n_sect - 1];
uint64_t value = sym.n_value - objSec.addr;
// Global defined symbol
if (sym.n_type & N_EXT) {
symbols.push_back(symtab->addDefined(name, isec, value));
continue;
}
// Local defined symbol
symbols.push_back(make<Defined>(name, isec, value));
}
}
// The relocations may refer to the symbols, so we parse them after we have
// parsed all the symbols.
for (size_t i = 0, n = subsections.size(); i < n; ++i)
parseRelocations(sectionHeaders[i], subsections[i]);
// the symbols loaded.
if (!sections.empty()) {
auto it = sections.begin();
for (const section_64 &sec : objSections) {
parseRelocations(sec, (*it)->relocs);
++it;
}
}
}
DylibFile::DylibFile(MemoryBufferRef mb, DylibFile *umbrella)
@ -409,8 +324,7 @@ void ArchiveFile::fetch(const object::Archive::Symbol &sym) {
sym.getName());
auto file = make<ObjFile>(mb);
symbols.insert(symbols.end(), file->symbols.begin(), file->symbols.end());
subsections.insert(subsections.end(), file->subsections.begin(),
file->subsections.end());
sections.insert(sections.end(), file->sections.begin(), file->sections.end());
}
// Returns "<internal>" or "baz.o".

18
lld/MachO/InputFiles.h
View File

@ -14,8 +14,6 @@
#include "llvm/BinaryFormat/MachO.h"
#include "llvm/Object/Archive.h"
#include "llvm/Support/MemoryBuffer.h"
#include <map>
#include <vector>
namespace lld {
@ -25,11 +23,6 @@ class InputSection;
class Symbol;
struct Reloc;
// If .subsections_via_symbols is set, each InputSection will be split along
// symbol boundaries. The keys of a SubsectionMap represent the offsets of
// each subsection from the start of the original pre-split InputSection.
using SubsectionMap = std::map<uint32_t, InputSection *>;
class InputFile {
public:
enum Kind {
@ -44,18 +37,15 @@ public:
MemoryBufferRef mb;
std::vector<Symbol *> symbols;
ArrayRef<llvm::MachO::section_64> sectionHeaders;
std::vector<SubsectionMap> subsections;
std::vector<InputSection *> sections;
protected:
InputFile(Kind kind, MemoryBufferRef mb) : mb(mb), fileKind(kind) {}
void parseSections(ArrayRef<llvm::MachO::section_64>);
std::vector<InputSection *> parseSections(ArrayRef<llvm::MachO::section_64>);
void parseSymbols(ArrayRef<const llvm::MachO::nlist_64> nList,
const char *strtab, bool subsectionsViaSymbols);
void parseRelocations(const llvm::MachO::section_64 &, SubsectionMap &);
void parseRelocations(const llvm::MachO::section_64 &,
std::vector<Reloc> &relocs);
private:
const Kind fileKind;

9
lld/MachO/InputSection.cpp
View File

@ -32,6 +32,7 @@ void InputSection::writeTo(uint8_t *buf) {
for (Reloc &r : relocs) {
uint64_t va = 0;
uint64_t addend = r.addend;
if (auto *s = r.target.dyn_cast<Symbol *>()) {
if (auto *dylibSymbol = dyn_cast<DylibSymbol>(s)) {
va = target->getDylibSymbolVA(*dylibSymbol, r.type);
@ -40,9 +41,15 @@ void InputSection::writeTo(uint8_t *buf) {
}
} else if (auto *isec = r.target.dyn_cast<InputSection *>()) {
va = isec->getVA();
// The implicit addend for pcrel section relocations is the pcrel offset
// in terms of the addresses in the input file. Here we adjust it so that
// it describes the offset from the start of the target section.
// TODO: Figure out what to do for non-pcrel section relocations.
// TODO: The offset of 4 is probably not right for ARM64.
addend -= isec->header->addr - (header->addr + r.offset + 4);
}
uint64_t val = va + r.addend;
uint64_t val = va + addend;
if (1) // TODO: handle non-pcrel relocations
val -= getVA() + r.offset;
target->relocateOne(buf + r.offset, r.type, val);

6
lld/MachO/InputSection.h
View File

@ -24,11 +24,7 @@ class Symbol;
struct Reloc {
uint8_t type;
// Adding this offset to the address of the target symbol or subsection gives
// the destination that this relocation refers to.
uint32_t addend;
// The offset from the start of the subsection that this relocation belongs
// to.
uint32_t offset;
llvm::PointerUnion<Symbol *, InputSection *> target;
};
@ -46,6 +42,8 @@ public:
InputFile *file = nullptr;
StringRef name;
StringRef segname;
// This provides access to the address of the section in the input file.
const llvm::MachO::section_64 *header;
OutputSection *parent = nullptr;
uint64_t outSecOff = 0;

47
lld/test/MachO/subsections-section-relocs.s
View File

@ -1,47 +0,0 @@
# REQUIRES: x86
# RUN: mkdir -p %t
# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t/test.o
# RUN: echo "_bar_str" > %t/order-file
# RUN: echo "_foo_str" >> %t/order-file
# RUN: lld -flavor darwinnew -o %t/test %t/test.o -order_file %t/order-file
# RUN: llvm-objdump --section-headers -d --no-show-raw-insn %t/test | FileCheck %s
# CHECK-LABEL: Sections:
# CHECK: __cstring {{[^ ]*}} {{0*}}[[#%x, CSTRING_ADDR:]]
# CHECK-LABEL: Disassembly of section __TEXT,__text:
## L._str should end up at CSTRING_ADDR + 4, and leaq is 7 bytes long so we
## have RIP = ADDR + 7
# CHECK: [[#%x, ADDR:]]: leaq
# CHECK-SAME: [[#%u, CSTRING_ADDR + 4 - ADDR - 7]](%rip), %rsi {{.*}} <_bar_str+0x4>
# RUN: llvm-readobj --string-dump=__cstring %t/test | FileCheck %s --check-prefix=STRINGS
# STRINGS: bar
# STRINGS: Private symbol
# STRINGS: foo
.text
.globl _main, _foo_str, _bar_str
_main:
leaq L_.str(%rip), %rsi
mov $0, %rax
ret
.section __TEXT,__cstring
_foo_str:
.asciz "foo"
_bar_str:
.asciz "bar"
## References to this generate a section relocation
## N.B.: ld64 doesn't actually reorder symbols in __cstring based on the order
## file. Only our implementation does. However, I'm not sure how else to
## test section relocations that target an address inside a relocated
## symbol: using a non-__cstring section would cause llvm-mc to emit a
## symbol relocation instead using the nearest symbol.
L_.str:
.asciz "Private symbol"
.subsections_via_symbols

55
lld/test/MachO/subsections-symbol-relocs.s
View File

@ -1,55 +0,0 @@
# REQUIRES: x86
# RUN: mkdir -p %t
# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t/test.o
# RUN: echo "_bar" > %t/order-file-1
# RUN: echo "_foo" >> %t/order-file-1
# RUN: echo "_main" >> %t/order-file-1
## _qux is marked as .alt_entry, so it should not create a new subsection and
## its contents should move with _bar to the start of the output despite the
## order file listing it at the end.
# RUN: echo "_qux" >> %t/order-file-1
## _bar and _baz point to the same address, so both order files should achieve
## the same result.
# RUN: echo "_baz" > %t/order-file-2
# RUN: echo "_foo" >> %t/order-file-2
# RUN: echo "_main" >> %t/order-file-2
# RUN: echo "_qux" >> %t/order-file-2
# RUN: lld -flavor darwinnew -o %t/test-1 %t/test.o -order_file %t/order-file-1
# RUN: llvm-objdump -d --no-show-raw-insn %t/test-1 | FileCheck %s
# RUN: lld -flavor darwinnew -o %t/test-2 %t/test.o -order_file %t/order-file-2
# RUN: llvm-objdump -d --no-show-raw-insn %t/test-2 | FileCheck %s
# CHECK-LABEL: Disassembly of section __TEXT,__text:
# CHECK: <_bar>:
# CHECK-NEXT: callq {{.*}} <_foo>
# CHECK-EMPTY:
# CHECK-NEXT: <_qux>:
# CHECK-NEXT: retq
# CHECK: <_foo>:
# CHECK-NEXT: retq
# CHECK: <_main>:
# CHECK-NEXT: callq {{.*}} <_bar>
# CHECK-NEXT: movq $0, %rax
# CHECK-NEXT: retq
.text
.globl _main, _foo, _bar, _qux
.alt_entry _qux
_foo:
retq
_main:
callq _bar
movq $0, %rax
retq
_bar:
_baz:
callq _foo
_qux:
retq
.subsections_via_symbols