[ELF] Merge relaIplt into relaDyn
`relaIplt` was added so that IRELATIVE relocations are placed at the end
of .rela.dyn (since https://reviews.llvm.org/D65651) or .rela.plt
(--pack-dyn-relocs=android[+relr]). Unfortunately, handling `relaIplt`
requires special cases all over the code base. We can extend
partitionRels/computeRels to partition both RELATIVE and IRELATIVE
relocations, rendering `relaIplt` unneeded.
The change allows IRELATIVE relocations in the DT_ANDROID_REL[A] table
(untested?!), which may be processed before other types of relocations.
This seems acceptable for Bionic's DEFINE_IFUNC_FOR use cases.
In addition, this change simplies changing .rel[a].dyn to a compact
relocation format (CREL).
SHF_INFO_LINK is removed from .rel[a].dyn with IRELATIVE relocations.
(See https://reviews.llvm.org/D89828).
GitOrigin-RevId: 18a49f03aa2b6bfeb073648b9eb75277a2386fc4
diff --git a/ELF/Relocations.cpp b/ELF/Relocations.cpp
index 92a1b9b..33c5013 100644
--- a/ELF/Relocations.cpp
+++ b/ELF/Relocations.cpp
@@ -1620,12 +1620,8 @@
// relatively straightforward. We create a PLT entry in Iplt, which is
// usually at the end of .plt, which makes an indirect call using a
// matching GOT entry in igotPlt, which is usually at the end of .got.plt.
- // The GOT entry is relocated using an IRELATIVE relocation in relaIplt,
- // which is usually at the end of .rela.plt. Unlike most relocations in
- // .rela.plt, which may be evaluated lazily without -z now, dynamic
- // loaders evaluate IRELATIVE relocs eagerly, which means that for
- // IRELATIVE relocs only, GOT-generating relocations can point directly to
- // .got.plt without requiring a separate GOT entry.
+ // The GOT entry is relocated using an IRELATIVE relocation in relaDyn,
+ // which is usually at the end of .rela.dyn.
//
// - Despite the fact that an ifunc does not have a fixed value, compilers
// that are not passed -fPIC will assume that they do, and will emit
@@ -1665,7 +1661,7 @@
// section/value fixed.
auto *directSym = makeDefined(cast<Defined>(sym));
directSym->allocateAux();
- addPltEntry(*in.iplt, *in.igotPlt, *in.relaIplt, target->iRelativeRel,
+ addPltEntry(*in.iplt, *in.igotPlt, *mainPart->relaDyn, target->iRelativeRel,
*directSym);
sym.allocateAux();
symAux.back().pltIdx = symAux[directSym->auxIdx].pltIdx;
diff --git a/ELF/SyntheticSections.cpp b/ELF/SyntheticSections.cpp
index 10eda17..f924756 100644
--- a/ELF/SyntheticSections.cpp
+++ b/ELF/SyntheticSections.cpp
@@ -1267,15 +1267,12 @@
// The output section .rela.dyn may include these synthetic sections:
//
// - part.relaDyn
-// - in.relaIplt: this is included if in.relaIplt is named .rela.dyn
// - in.relaPlt: this is included if a linker script places .rela.plt inside
// .rela.dyn
//
// DT_RELASZ is the total size of the included sections.
static uint64_t addRelaSz(const RelocationBaseSection &relaDyn) {
size_t size = relaDyn.getSize();
- if (in.relaIplt->getParent() == relaDyn.getParent())
- size += in.relaIplt->getSize();
if (in.relaPlt->getParent() == relaDyn.getParent())
size += in.relaPlt->getSize();
return size;
@@ -1372,9 +1369,7 @@
if (!config->shared && !config->relocatable && !config->zRodynamic)
addInt(DT_DEBUG, 0);
- if (part.relaDyn->isNeeded() ||
- (in.relaIplt->isNeeded() &&
- part.relaDyn->getParent() == in.relaIplt->getParent())) {
+ if (part.relaDyn->isNeeded()) {
addInSec(part.relaDyn->dynamicTag, *part.relaDyn);
entries.emplace_back(part.relaDyn->sizeDynamicTag,
addRelaSz(*part.relaDyn));
@@ -1657,10 +1652,6 @@
getParent()->flags |= ELF::SHF_INFO_LINK;
getParent()->info = in.gotPlt->getParent()->sectionIndex;
}
- if (in.relaIplt.get() == this && in.igotPlt->getParent()) {
- getParent()->flags |= ELF::SHF_INFO_LINK;
- getParent()->info = in.igotPlt->getParent()->sectionIndex;
- }
}
void DynamicReloc::computeRaw(SymbolTableBaseSection *symtab) {
@@ -1674,6 +1665,11 @@
SymbolTableBaseSection *symTab = getPartition().dynSymTab.get();
parallelForEach(relocs,
[symTab](DynamicReloc &rel) { rel.computeRaw(symTab); });
+
+ auto irelative = std::partition(
+ relocs.begin() + numRelativeRelocs, relocs.end(),
+ [t = target->iRelativeRel](auto &r) { return r.type != t; });
+
// 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.
@@ -1682,7 +1678,7 @@
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.
- llvm::sort(nonRelative, relocs.end(), [&](auto &a, auto &b) {
+ llvm::sort(nonRelative, irelative, [&](auto &a, auto &b) {
return std::tie(a.r_sym, a.r_offset) < std::tie(b.r_sym, b.r_offset);
});
}
@@ -3843,7 +3839,6 @@
ppc32Got2.reset();
ibtPlt.reset();
relaPlt.reset();
- relaIplt.reset();
shStrTab.reset();
strTab.reset();
symTab.reset();
diff --git a/ELF/SyntheticSections.h b/ELF/SyntheticSections.h
index b41e694..fa21b80 100644
--- a/ELF/SyntheticSections.h
+++ b/ELF/SyntheticSections.h
@@ -1358,7 +1358,6 @@
std::unique_ptr<PPC32Got2Section> ppc32Got2;
std::unique_ptr<IBTPltSection> ibtPlt;
std::unique_ptr<RelocationBaseSection> relaPlt;
- std::unique_ptr<RelocationBaseSection> relaIplt;
std::unique_ptr<StringTableSection> shStrTab;
std::unique_ptr<StringTableSection> strTab;
std::unique_ptr<SymbolTableBaseSection> symTab;
diff --git a/ELF/Writer.cpp b/ELF/Writer.cpp
index 4eca7b2..40d617b 100644
--- a/ELF/Writer.cpp
+++ b/ELF/Writer.cpp
@@ -449,8 +449,8 @@
add(*part.dynamic);
add(*part.dynStrTab);
- add(*part.relaDyn);
}
+ add(*part.relaDyn);
if (config->relrPackDynRelocs) {
part.relrDyn = std::make_unique<RelrSection<ELFT>>(threadCount);
@@ -550,17 +550,6 @@
/*threadCount=*/1);
add(*in.relaPlt);
- // The relaIplt immediately follows .rel[a].dyn to ensure that the IRelative
- // relocations are processed last by the dynamic loader. We cannot place the
- // iplt section in .rel.dyn when Android relocation packing is enabled because
- // that would cause a section type mismatch. However, because the Android
- // dynamic loader reads .rel.plt after .rel.dyn, we can get the desired
- // behaviour by placing the iplt section in .rel.plt.
- in.relaIplt = std::make_unique<RelocationSection<ELFT>>(
- config->androidPackDynRelocs ? in.relaPlt->name : relaDynName,
- /*sort=*/false, /*threadCount=*/1);
- add(*in.relaIplt);
-
if ((config->emachine == EM_386 || config->emachine == EM_X86_64) &&
(config->andFeatures & GNU_PROPERTY_X86_FEATURE_1_IBT)) {
in.ibtPlt = std::make_unique<IBTPltSection>();
@@ -1071,20 +1060,18 @@
sec->ptLoad = this;
}
-// The beginning and the ending of .rel[a].plt section are marked
-// with __rel[a]_iplt_{start,end} symbols if it is a statically linked
-// executable. The runtime needs these symbols in order to resolve
-// all IRELATIVE relocs on startup. For dynamic executables, we don't
-// need these symbols, since IRELATIVE relocs are resolved through GOT
-// and PLT. For details, see http://www.airs.com/blog/archives/403.
+// A statically linked position-dependent executable should only contain
+// IRELATIVE relocations and no other dynamic relocations. Encapsulation symbols
+// __rel[a]_iplt_{start,end} will be defined for .rel[a].dyn, to be
+// processed by the libc runtime. Other executables or DSOs use dynamic tags
+// instead.
template <class ELFT> void Writer<ELFT>::addRelIpltSymbols() {
if (config->isPic)
return;
- // By default, __rela_iplt_{start,end} belong to a dummy section 0
- // because .rela.plt might be empty and thus removed from output.
- // We'll override Out::elfHeader with In.relaIplt later when we are
- // sure that .rela.plt exists in output.
+ // __rela_iplt_{start,end} are initially defined relative to dummy section 0.
+ // We'll override Out::elfHeader with relaDyn later when we are sure that
+ // .rela.dyn will be present in the output.
ElfSym::relaIpltStart = addOptionalRegular(
config->isRela ? "__rela_iplt_start" : "__rel_iplt_start",
Out::elfHeader, 0, STV_HIDDEN);
@@ -1110,11 +1097,11 @@
ElfSym::globalOffsetTable->section = sec;
}
- // .rela_iplt_{start,end} mark the start and the end of in.relaIplt.
- if (ElfSym::relaIpltStart && in.relaIplt->isNeeded()) {
- ElfSym::relaIpltStart->section = in.relaIplt.get();
- ElfSym::relaIpltEnd->section = in.relaIplt.get();
- ElfSym::relaIpltEnd->value = in.relaIplt->getSize();
+ // .rela_iplt_{start,end} mark the start and the end of .rel[a].dyn.
+ if (ElfSym::relaIpltStart && mainPart->relaDyn->isNeeded()) {
+ ElfSym::relaIpltStart->section = mainPart->relaDyn.get();
+ ElfSym::relaIpltEnd->section = mainPart->relaDyn.get();
+ ElfSym::relaIpltEnd->value = mainPart->relaDyn->getSize();
}
PhdrEntry *last = nullptr;
@@ -1470,14 +1457,6 @@
if (name == ".init" || name == ".fini")
return;
- // IRelative relocations that usually live in the .rel[a].dyn section should
- // be processed last by the dynamic loader. To achieve that we add synthetic
- // sections in the required order from the beginning so that the in.relaIplt
- // section is placed last in an output section. Here we just do not apply
- // sorting for an output section which holds the in.relaIplt section.
- if (in.relaIplt->getParent() == &osec)
- return;
-
// Sort input sections by priority using the list provided by
// --symbol-ordering-file or --shuffle-sections=. This is a least significant
// digit radix sort. The sections may be sorted stably again by a more
@@ -2196,7 +2175,6 @@
finalizeSynthetic(in.mipsGot.get());
finalizeSynthetic(in.igotPlt.get());
finalizeSynthetic(in.gotPlt.get());
- finalizeSynthetic(in.relaIplt.get());
finalizeSynthetic(in.relaPlt.get());
finalizeSynthetic(in.plt.get());
finalizeSynthetic(in.iplt.get());
diff --git a/test/ELF/aarch64-gnu-ifunc.s b/test/ELF/aarch64-gnu-ifunc.s
index dee2477..d76b54e 100644
--- a/test/ELF/aarch64-gnu-ifunc.s
+++ b/test/ELF/aarch64-gnu-ifunc.s
@@ -11,13 +11,12 @@
// CHECK-NEXT: Type: SHT_RELA
// CHECK-NEXT: Flags [
// CHECK-NEXT: SHF_ALLOC
-// CHECK-NEXT: SHF_INFO_LINK
// CHECK-NEXT: ]
// CHECK-NEXT: Address: [[RELA:.*]]
// CHECK-NEXT: Offset: 0x158
// CHECK-NEXT: Size: 48
// CHECK-NEXT: Link: 0
-// CHECK-NEXT: Info: 4
+// CHECK-NEXT: Info: 0
// CHECK-NEXT: AddressAlignment: 8
// CHECK-NEXT: EntrySize: 24
// CHECK-NEXT: }
diff --git a/test/ELF/arm-gnu-ifunc.s b/test/ELF/arm-gnu-ifunc.s
index 5624782..d49ca18 100644
--- a/test/ELF/arm-gnu-ifunc.s
+++ b/test/ELF/arm-gnu-ifunc.s
@@ -30,13 +30,12 @@
// CHECK-NEXT: Type: SHT_REL
// CHECK-NEXT: Flags [
// CHECK-NEXT: SHF_ALLOC
-// CHECK-NEXT: SHF_INFO_LINK
// CHECK-NEXT: ]
// CHECK-NEXT: Address: 0x100F4
// CHECK-NEXT: Offset: 0xF4
// CHECK-NEXT: Size: 16
// CHECK-NEXT: Link:
-// CHECK-NEXT: Info: 4
+// CHECK-NEXT: Info: 0
// CHECK: Name: .iplt
// CHECK-NEXT: Type: SHT_PROGBITS
// CHECK-NEXT: Flags [
diff --git a/test/ELF/gnu-ifunc-i386.s b/test/ELF/gnu-ifunc-i386.s
index b502fd6..43b19b2 100644
--- a/test/ELF/gnu-ifunc-i386.s
+++ b/test/ELF/gnu-ifunc-i386.s
@@ -11,13 +11,12 @@
// CHECK-NEXT: Type: SHT_REL
// CHECK-NEXT: Flags [
// CHECK-NEXT: SHF_ALLOC
-// CHECK-NEXT: SHF_INFO_LINK
// CHECK-NEXT: ]
// CHECK-NEXT: Address: [[RELA:.*]]
// CHECK-NEXT: Offset: 0xD4
// CHECK-NEXT: Size: 16
// CHECK-NEXT: Link: 0
-// CHECK-NEXT: Info: 4
+// CHECK-NEXT: Info: 0
// CHECK-NEXT: AddressAlignment: 4
// CHECK-NEXT: EntrySize: 8
// CHECK-NEXT: }
diff --git a/test/ELF/systemz-ifunc-nonpreemptible.s b/test/ELF/systemz-ifunc-nonpreemptible.s
index 5056db3..892bbde 100644
--- a/test/ELF/systemz-ifunc-nonpreemptible.s
+++ b/test/ELF/systemz-ifunc-nonpreemptible.s
@@ -10,7 +10,7 @@
# CHECK: Section Headers:
# CHECK-NEXT: [Nr] Name Type Address Off Size ES Flg Lk Inf Al
# CHECK-NEXT: [ 0] NULL 0000000000000000 000000 000000 00 0 0 0
-# CHECK-NEXT: [ 1] .rela.dyn RELA 0000000001000158 000158 000030 18 AI 0 4 8
+# CHECK-NEXT: [ 1] .rela.dyn RELA 0000000001000158 000158 000030 18 A 0 0 8
# CHECK-NEXT: [ 2] .text PROGBITS 0000000001001188 000188 00001c 00 AX 0 0 4
# CHECK-NEXT: [ 3] .iplt PROGBITS 00000000010011b0 0001b0 000040 00 AX 0 0 16
# CHECK-NEXT: [ 4] .got.plt PROGBITS 00000000010021f0 0001f0 000010 00 WA 0 0 8
