Skip to content

Commit

Permalink
[ELF] Refactor -z combreloc
Browse files Browse the repository at this point in the history 
* `RelocationBaseSection::addReloc` increases `numRelativeRelocs`, which
  duplicates the work done by RelocationSection<ELFT>::writeTo.
* --pack-dyn-relocs=android has inappropropriate DT_RELACOUNT.
  AndroidPackedRelocationSection does not necessarily place relative relocations
  in the front and DT_RELACOUNT might cause semantics error (though our
  implementation doesn't and Android bionic doesn't use DT_RELACOUNT anyway.)

Move `llvm::partition` to a new function `partitionRels` and compute
`numRelativeRelocs` there. Now `RelocationBaseSection::addReloc` is trivial and
can be moved to the header to enable inlining.

The rest of DynamicReloc and `-z combreloc` handling is moved to the
non-template `RelocationBaseSection::computeRels` to decrease code size. My
x86-64 lld executable is 44+KiB smaller.

While here, rename `sort` to `combreloc`.
  • Loading branch information
@MaskRay
MaskRay committed Jan 29, 2022
1 parent 460830a commit da0e5b8
Show file tree
Hide file tree
Showing 4 changed files with 101 additions and 94 deletions.
74 changes: 37 additions & 37 deletions lld/ELF/SyntheticSections.cpp
View file
Expand Up @@ -1589,9 +1589,11 @@ uint32_t DynamicReloc::getSymIndex(SymbolTableBaseSection *symTab) const {

RelocationBaseSection::RelocationBaseSection(StringRef name, uint32_t type,
int32_t dynamicTag,
int32_t sizeDynamicTag)
int32_t sizeDynamicTag,
bool combreloc)
: SyntheticSection(SHF_ALLOC, type, config->wordsize, name),
dynamicTag(dynamicTag), sizeDynamicTag(sizeDynamicTag) {}
dynamicTag(dynamicTag), sizeDynamicTag(sizeDynamicTag),
combreloc(combreloc) {}

void RelocationBaseSection::addSymbolReloc(RelType dynType,
InputSectionBase &isec,
Expand Down Expand Up @@ -1640,10 +1642,13 @@ void RelocationBaseSection::addReloc(DynamicReloc::Kind kind, RelType dynType,
addReloc({dynType, &inputSec, offsetInSec, kind, sym, addend, expr});
}

void RelocationBaseSection::addReloc(const DynamicReloc &reloc) {
if (reloc.type == target->relativeRel)
++numRelativeRelocs;
relocs.push_back(reloc);
void RelocationBaseSection::partitionRels() {
if (!combreloc)
return;
const RelType relativeRel = target->relativeRel;
numRelativeRelocs =
llvm::partition(relocs, [=](auto &r) { return r.type == relativeRel; }) -
relocs.begin();
}

void RelocationBaseSection::finalizeContents() {
Expand All @@ -1667,69 +1672,64 @@ void RelocationBaseSection::finalizeContents() {
}
}

RelrBaseSection::RelrBaseSection()
: SyntheticSection(SHF_ALLOC,
config->useAndroidRelrTags ? SHT_ANDROID_RELR : SHT_RELR,
config->wordsize, ".relr.dyn") {}

template <class ELFT>
static void encodeDynamicReloc(typename ELFT::Rela *p,
const DynamicReloc &rel) {
p->r_offset = rel.r_offset;
p->setSymbolAndType(rel.r_sym, rel.type, config->isMips64EL);
if (config->isRela)
p->r_addend = rel.addend;
}

void DynamicReloc::computeRaw(SymbolTableBaseSection *symtab) {
r_offset = getOffset();
r_sym = getSymIndex(symtab);
addend = computeAddend();
kind = AddendOnly; // Catch errors
}

template <class ELFT>
RelocationSection<ELFT>::RelocationSection(StringRef name, bool sort)
: RelocationBaseSection(name, config->isRela ? SHT_RELA : SHT_REL,
config->isRela ? DT_RELA : DT_REL,
config->isRela ? DT_RELASZ : DT_RELSZ),
sort(sort) {
this->entsize = config->isRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
}

template <class ELFT> void RelocationSection<ELFT>::writeTo(uint8_t *buf) {
void RelocationBaseSection::computeRels() {
SymbolTableBaseSection *symTab = getPartition().dynSymTab.get();

parallelForEach(relocs,
[symTab](DynamicReloc &rel) { rel.computeRaw(symTab); });
// Sort by (!IsRelative,SymIndex,r_offset). DT_REL[A]COUNT requires us to
// place R_*_RELATIVE first. SymIndex is to improve locality, while r_offset
// is to make results easier to read.
if (sort) {
const RelType relativeRel = target->relativeRel;
auto nonRelative =
llvm::partition(relocs, [=](auto &r) { return r.type == relativeRel; });
if (combreloc) {
auto nonRelative = relocs.begin() + numRelativeRelocs;
parallelSort(relocs.begin(), nonRelative,
[&](auto &a, auto &b) { return a.r_offset < b.r_offset; });
// Non-relative relocations are few, so don't bother with parallelSort.
std::sort(nonRelative, relocs.end(), [&](auto &a, auto &b) {
return std::tie(a.r_sym, a.r_offset) < std::tie(b.r_sym, b.r_offset);
});
}
}

template <class ELFT>
RelocationSection<ELFT>::RelocationSection(StringRef name, bool combreloc)
: RelocationBaseSection(name, config->isRela ? SHT_RELA : SHT_REL,
config->isRela ? DT_RELA : DT_REL,
config->isRela ? DT_RELASZ : DT_RELSZ, combreloc) {
this->entsize = config->isRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
}

template <class ELFT> void RelocationSection<ELFT>::writeTo(uint8_t *buf) {
computeRels();
for (const DynamicReloc &rel : relocs) {
encodeDynamicReloc<ELFT>(reinterpret_cast<Elf_Rela *>(buf), rel);
auto *p = reinterpret_cast<Elf_Rela *>(buf);
p->r_offset = rel.r_offset;
p->setSymbolAndType(rel.r_sym, rel.type, config->isMips64EL);
if (config->isRela)
p->r_addend = rel.addend;
buf += config->isRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
}
}

RelrBaseSection::RelrBaseSection()
: SyntheticSection(SHF_ALLOC,
config->useAndroidRelrTags ? SHT_ANDROID_RELR : SHT_RELR,
config->wordsize, ".relr.dyn") {}

template <class ELFT>
AndroidPackedRelocationSection<ELFT>::AndroidPackedRelocationSection(
StringRef name)
: RelocationBaseSection(
name, config->isRela ? SHT_ANDROID_RELA : SHT_ANDROID_REL,
config->isRela ? DT_ANDROID_RELA : DT_ANDROID_REL,
config->isRela ? DT_ANDROID_RELASZ : DT_ANDROID_RELSZ) {
config->isRela ? DT_ANDROID_RELASZ : DT_ANDROID_RELSZ,
/*combreloc=*/false) {
this->entsize = 1;
}

Expand Down
14 changes: 7 additions & 7 deletions lld/ELF/SyntheticSections.h
View file
Expand Up @@ -515,11 +515,11 @@ template <class ELFT> class DynamicSection final : public SyntheticSection {
class RelocationBaseSection : public SyntheticSection {
public:
RelocationBaseSection(StringRef name, uint32_t type, int32_t dynamicTag,
int32_t sizeDynamicTag);
int32_t sizeDynamicTag, bool combreloc);
/// Add a dynamic relocation without writing an addend to the output section.
/// This overload can be used if the addends are written directly instead of
/// using relocations on the input section (e.g. MipsGotSection::writeTo()).
void addReloc(const DynamicReloc &reloc);
void addReloc(const DynamicReloc &reloc) { relocs.push_back(reloc); }
/// Add a dynamic relocation against \p sym with an optional addend.
void addSymbolReloc(RelType dynType, InputSectionBase &isec,
uint64_t offsetInSec, Symbol &sym, int64_t addend = 0,
Expand All @@ -541,6 +541,7 @@ class RelocationBaseSection : public SyntheticSection {
bool isNeeded() const override { return !relocs.empty(); }
size_t getSize() const override { return relocs.size() * this->entsize; }
size_t getRelativeRelocCount() const { return numRelativeRelocs; }
void partitionRels();
void finalizeContents() override;
static bool classof(const SectionBase *d) {
return SyntheticSection::classof(d) &&
Expand All @@ -551,7 +552,9 @@ class RelocationBaseSection : public SyntheticSection {
SmallVector<DynamicReloc, 0> relocs;

protected:
size_t numRelativeRelocs = 0;
void computeRels();
size_t numRelativeRelocs = 0; // used by -z combreloc
bool combreloc;
};

template <class ELFT>
Expand All @@ -560,11 +563,8 @@ class RelocationSection final : public RelocationBaseSection {
using Elf_Rela = typename ELFT::Rela;

public:
RelocationSection(StringRef name, bool sort);
RelocationSection(StringRef name, bool combreloc);
void writeTo(uint8_t *buf) override;

private:
bool sort;
};

template <class ELFT>
Expand Down
7 changes: 6 additions & 1 deletion lld/ELF/Writer.cpp
View file
Expand Up @@ -2086,11 +2086,16 @@ template <class ELFT> void Writer<ELFT>::finalizeSections() {
// Dynamic section must be the last one in this list and dynamic
// symbol table section (dynSymTab) must be the first one.
for (Partition &part : partitions) {
if (part.relaDyn) {
// Compute DT_RELACOUNT to be used by part.dynamic.
part.relaDyn->partitionRels();
finalizeSynthetic(part.relaDyn.get());
}

finalizeSynthetic(part.dynSymTab.get());
finalizeSynthetic(part.gnuHashTab.get());
finalizeSynthetic(part.hashTab.get());
finalizeSynthetic(part.verDef.get());
finalizeSynthetic(part.relaDyn.get());
finalizeSynthetic(part.relrDyn.get());
finalizeSynthetic(part.ehFrameHdr.get());
finalizeSynthetic(part.verSym.get());
Expand Down
100 changes: 51 additions & 49 deletions lld/test/ELF/pack-dyn-relocs.s
View file
Expand Up @@ -77,42 +77,43 @@
/// by the larger groups of relative relocations (i.e. the 8 and 9 followed
/// by the 7.)
// ANDROID32: Section ({{.+}}) .rel.dyn {
// ANDROID32-NEXT: 0x3024C R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x30250 R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x30254 R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x30258 R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x3025C R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x30260 R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x30264 R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x30268 R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x3026C R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x30270 R_ARM_RELATIVE -

// ANDROID32-NEXT: 0x30294 R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x30298 R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x3029C R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x302A0 R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x302A4 R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x302A8 R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x302AC R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x302B0 R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x302B4 R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x302B8 R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x302BC R_ARM_RELATIVE -

// ANDROID32-NEXT: 0x30270 R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x30274 R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x30278 R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x3027C R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x30280 R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x30284 R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x30288 R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x3028C R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x30290 R_ARM_RELATIVE -
// ANDROID32-NEXT: 0x302C1 R_ARM_RELATIVE -

// ANDROID32-NEXT: 0x30274 R_ARM_ABS32 bar2
// ANDROID32-NEXT: 0x30298 R_ARM_ABS32 bar2
// ANDROID32-NEXT: 0x302B9 R_ARM_RELATIVE -

// ANDROID32-NEXT: 0x3026C R_ARM_ABS32 bar2
// ANDROID32-NEXT: 0x30290 R_ARM_ABS32 bar2
// ANDROID32-NEXT: 0x302BD R_ARM_ABS32 bar2
// ANDROID32-NEXT: 0x302C1 R_ARM_ABS32 bar2
// ANDROID32-NEXT: 0x302C5 R_ARM_ABS32 bar2
// ANDROID32-NEXT: 0x302C9 R_ARM_ABS32 bar2
// ANDROID32-NEXT: 0x302CD R_ARM_ABS32 bar2
// ANDROID32-NEXT: 0x302D1 R_ARM_ABS32 bar2
// ANDROID32-NEXT: 0x302D5 R_ARM_ABS32 bar2

// ANDROID32-NEXT: 0x30294 R_ARM_ABS32 zed2 0x0
// ANDROID32-NEXT: 0x3028C R_ARM_ABS32 zed2
// ANDROID32-NEXT: }

// RUN: ld.lld -pie --pack-dyn-relocs=relr %t.a32.o %t.a32.so -o %t4.a32
Expand Down Expand Up @@ -225,6 +226,7 @@
// UNPACKED64-NEXT: 0x30760 R_AARCH64_RELATIVE - 0x9

// UNPACKED64-NEXT: 0x30769 R_AARCH64_RELATIVE - 0xA

// UNPACKED64-NEXT: 0x306D0 R_AARCH64_ABS64 bar2 0x1
// UNPACKED64-NEXT: 0x30718 R_AARCH64_ABS64 bar2 0x0
// UNPACKED64-NEXT: 0x30771 R_AARCH64_ABS64 bar2 0x0
Expand Down Expand Up @@ -259,42 +261,42 @@
// ANDROID64-HEADERS: 0x0000000060000012 ANDROID_RELASZ [[SIZE]]

// ANDROID64: Section ({{.+}}) .rela.dyn {
// ANDROID64-NEXT: 0x303F0 R_AARCH64_RELATIVE - 0x1
// ANDROID64-NEXT: 0x303F8 R_AARCH64_RELATIVE - 0x2
// ANDROID64-NEXT: 0x30400 R_AARCH64_RELATIVE - 0x3
// ANDROID64-NEXT: 0x30408 R_AARCH64_RELATIVE - 0x4
// ANDROID64-NEXT: 0x30410 R_AARCH64_RELATIVE - 0x5
// ANDROID64-NEXT: 0x30418 R_AARCH64_RELATIVE - 0x6
// ANDROID64-NEXT: 0x30420 R_AARCH64_RELATIVE - 0x7
// ANDROID64-NEXT: 0x30428 R_AARCH64_RELATIVE - 0x8

// ANDROID64-NEXT: 0x30480 R_AARCH64_RELATIVE - 0x1
// ANDROID64-NEXT: 0x30488 R_AARCH64_RELATIVE - 0x2
// ANDROID64-NEXT: 0x30490 R_AARCH64_RELATIVE - 0x3
// ANDROID64-NEXT: 0x30498 R_AARCH64_RELATIVE - 0x4
// ANDROID64-NEXT: 0x304A0 R_AARCH64_RELATIVE - 0x5
// ANDROID64-NEXT: 0x304A8 R_AARCH64_RELATIVE - 0x6
// ANDROID64-NEXT: 0x304B0 R_AARCH64_RELATIVE - 0x7
// ANDROID64-NEXT: 0x304B8 R_AARCH64_RELATIVE - 0x8
// ANDROID64-NEXT: 0x304C0 R_AARCH64_RELATIVE - 0x9

// ANDROID64-NEXT: 0x30438 R_AARCH64_RELATIVE - 0x1
// ANDROID64-NEXT: 0x30440 R_AARCH64_RELATIVE - 0x2
// ANDROID64-NEXT: 0x30448 R_AARCH64_RELATIVE - 0x3
// ANDROID64-NEXT: 0x30450 R_AARCH64_RELATIVE - 0x4
// ANDROID64-NEXT: 0x30458 R_AARCH64_RELATIVE - 0x5
// ANDROID64-NEXT: 0x30460 R_AARCH64_RELATIVE - 0x6
// ANDROID64-NEXT: 0x30468 R_AARCH64_RELATIVE - 0x7
// ANDROID64-NEXT: 0x304C9 R_AARCH64_RELATIVE - 0xA

// ANDROID64-NEXT: 0x30478 R_AARCH64_ABS64 bar2 0x0
// ANDROID64-NEXT: 0x304D1 R_AARCH64_ABS64 bar2 0x0
// ANDROID64-NEXT: 0x304D9 R_AARCH64_ABS64 bar2 0x0
// ANDROID64-NEXT: 0x304F1 R_AARCH64_ABS64 bar2 0x0
// ANDROID64-NEXT: 0x30430 R_AARCH64_ABS64 bar2 0x1
// ANDROID64-NEXT: 0x30470 R_AARCH64_ABS64 zed2 0x0
// ANDROID64-NEXT: 0x304E1 R_AARCH64_ABS64 bar2 0x1
// ANDROID64-NEXT: 0x304E9 R_AARCH64_ABS64 bar2 0x1
// ANDROID64-NEXT: 0x303E0 R_AARCH64_RELATIVE - 0x1
// ANDROID64-NEXT: 0x303E8 R_AARCH64_RELATIVE - 0x2
// ANDROID64-NEXT: 0x303F0 R_AARCH64_RELATIVE - 0x3
// ANDROID64-NEXT: 0x303F8 R_AARCH64_RELATIVE - 0x4
// ANDROID64-NEXT: 0x30400 R_AARCH64_RELATIVE - 0x5
// ANDROID64-NEXT: 0x30408 R_AARCH64_RELATIVE - 0x6
// ANDROID64-NEXT: 0x30410 R_AARCH64_RELATIVE - 0x7
// ANDROID64-NEXT: 0x30418 R_AARCH64_RELATIVE - 0x8
// ANDROID64-NEXT: 0x30470 R_AARCH64_RELATIVE - 0x1
// ANDROID64-NEXT: 0x30478 R_AARCH64_RELATIVE - 0x2
// ANDROID64-NEXT: 0x30480 R_AARCH64_RELATIVE - 0x3
// ANDROID64-NEXT: 0x30488 R_AARCH64_RELATIVE - 0x4
// ANDROID64-NEXT: 0x30490 R_AARCH64_RELATIVE - 0x5
// ANDROID64-NEXT: 0x30498 R_AARCH64_RELATIVE - 0x6
// ANDROID64-NEXT: 0x304A0 R_AARCH64_RELATIVE - 0x7
// ANDROID64-NEXT: 0x304A8 R_AARCH64_RELATIVE - 0x8
// ANDROID64-NEXT: 0x304B0 R_AARCH64_RELATIVE - 0x9

// ANDROID64-NEXT: 0x30428 R_AARCH64_RELATIVE - 0x1
// ANDROID64-NEXT: 0x30430 R_AARCH64_RELATIVE - 0x2
// ANDROID64-NEXT: 0x30438 R_AARCH64_RELATIVE - 0x3
// ANDROID64-NEXT: 0x30440 R_AARCH64_RELATIVE - 0x4
// ANDROID64-NEXT: 0x30448 R_AARCH64_RELATIVE - 0x5
// ANDROID64-NEXT: 0x30450 R_AARCH64_RELATIVE - 0x6
// ANDROID64-NEXT: 0x30458 R_AARCH64_RELATIVE - 0x7

// ANDROID64-NEXT: 0x304B9 R_AARCH64_RELATIVE - 0xA

// ANDROID64-NEXT: 0x30468 R_AARCH64_ABS64 bar2 0x0
// ANDROID64-NEXT: 0x304C1 R_AARCH64_ABS64 bar2 0x0
// ANDROID64-NEXT: 0x304C9 R_AARCH64_ABS64 bar2 0x0
// ANDROID64-NEXT: 0x304E1 R_AARCH64_ABS64 bar2 0x0
// ANDROID64-NEXT: 0x30420 R_AARCH64_ABS64 bar2 0x1
// ANDROID64-NEXT: 0x30460 R_AARCH64_ABS64 zed2 0x0
// ANDROID64-NEXT: 0x304D1 R_AARCH64_ABS64 bar2 0x1
// ANDROID64-NEXT: 0x304D9 R_AARCH64_ABS64 bar2 0x1
// ANDROID64-NEXT: }

// RUN: ld.lld -pie --pack-dyn-relocs=relr %t.a64.o %t.a64.so -o %t4.a64
Expand Down

0 comments on commit da0e5b8

Please sign in to comment.