[lld] r338247 - [ELF] - Implement SHT_SYMTAB_SHNDX (.symtab_shndxr) section.
George Rimar via llvm-commits
llvm-commits at lists.llvm.org
Mon Jul 30 05:39:54 PDT 2018
Author: grimar
Date: Mon Jul 30 05:39:54 2018
New Revision: 338247
URL: http://llvm.org/viewvc/llvm-project?rev=338247&view=rev
Log:
[ELF] - Implement SHT_SYMTAB_SHNDX (.symtab_shndxr) section.
This is relative to https://bugs.llvm.org//show_bug.cgi?id=38119.
SHT_SYMTAB section is able to keep symbols with output section indices
up to 0xff00 (SHN_LORESERVE). But if we have indices that are greater
than that (PR shows that it might happen), we need to use
SHT_SYMTAB_SHNDX extended section. It was not supported by LLD.
Description of the SHT_SYMTAB_SHNDX section is here:
https://docs.oracle.com/cd/E19683-01/817-3677/chapter6-94076/index.html.
Differential revision: https://reviews.llvm.org/D49541
Modified:
lld/trunk/ELF/SyntheticSections.cpp
lld/trunk/ELF/SyntheticSections.h
lld/trunk/ELF/Writer.cpp
lld/trunk/test/ELF/linkerscript/orphan-report.s
lld/trunk/test/ELF/relocatable-many-sections.s
Modified: lld/trunk/ELF/SyntheticSections.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/SyntheticSections.cpp?rev=338247&r1=338246&r2=338247&view=diff
==============================================================================
--- lld/trunk/ELF/SyntheticSections.cpp (original)
+++ lld/trunk/ELF/SyntheticSections.cpp Mon Jul 30 05:39:54 2018
@@ -1935,6 +1935,23 @@ SymbolTableSection<ELFT>::SymbolTableSec
this->Entsize = sizeof(Elf_Sym);
}
+static BssSection *getCommonSec(Symbol *Sym) {
+ if (!Config->DefineCommon)
+ if (auto *D = dyn_cast<Defined>(Sym))
+ return dyn_cast_or_null<BssSection>(D->Section);
+ return nullptr;
+}
+
+static uint32_t getSymSectionIndex(Symbol *Sym) {
+ if (getCommonSec(Sym))
+ return SHN_COMMON;
+ if (!isa<Defined>(Sym) || Sym->NeedsPltAddr)
+ return SHN_UNDEF;
+ if (const OutputSection *OS = Sym->getOutputSection())
+ return OS->SectionIndex >= SHN_LORESERVE ? SHN_XINDEX : OS->SectionIndex;
+ return SHN_ABS;
+}
+
// Write the internal symbol table contents to the output symbol table.
template <class ELFT> void SymbolTableSection<ELFT>::writeTo(uint8_t *Buf) {
// The first entry is a null entry as per the ELF spec.
@@ -1956,22 +1973,7 @@ template <class ELFT> void SymbolTableSe
}
ESym->st_name = Ent.StrTabOffset;
-
- // Set a section index.
- BssSection *CommonSec = nullptr;
- if (!Config->DefineCommon)
- if (auto *D = dyn_cast<Defined>(Sym))
- CommonSec = dyn_cast_or_null<BssSection>(D->Section);
- if (CommonSec)
- ESym->st_shndx = SHN_COMMON;
- else if (Sym->NeedsPltAddr)
- ESym->st_shndx = SHN_UNDEF;
- else if (const OutputSection *OutSec = Sym->getOutputSection())
- ESym->st_shndx = OutSec->SectionIndex;
- else if (isa<Defined>(Sym))
- ESym->st_shndx = SHN_ABS;
- else
- ESym->st_shndx = SHN_UNDEF;
+ ESym->st_shndx = getSymSectionIndex(Ent.Sym);
// Copy symbol size if it is a defined symbol. st_size is not significant
// for undefined symbols, so whether copying it or not is up to us if that's
@@ -1986,7 +1988,7 @@ template <class ELFT> void SymbolTableSe
// st_value is usually an address of a symbol, but that has a
// special meaining for uninstantiated common symbols (this can
// occur if -r is given).
- if (CommonSec)
+ if (BssSection *CommonSec = getCommonSec(Ent.Sym))
ESym->st_value = CommonSec->Alignment;
else
ESym->st_value = Sym->getVA();
@@ -2026,6 +2028,44 @@ template <class ELFT> void SymbolTableSe
}
}
+SymtabShndxSection::SymtabShndxSection()
+ : SyntheticSection(0, SHT_SYMTAB_SHNDX, 4, ".symtab_shndxr") {
+ this->Entsize = 4;
+}
+
+void SymtabShndxSection::writeTo(uint8_t *Buf) {
+ // We write an array of 32 bit values, where each value has 1:1 association
+ // with an entry in .symtab. If the corresponding entry contains SHN_XINDEX,
+ // we need to write actual index, otherwise, we must write SHN_UNDEF(0).
+ Buf += 4; // Ignore .symtab[0] entry.
+ for (const SymbolTableEntry &Entry : InX::SymTab->getSymbols()) {
+ if (getSymSectionIndex(Entry.Sym) == SHN_XINDEX)
+ write32(Buf, Entry.Sym->getOutputSection()->SectionIndex);
+ Buf += 4;
+ }
+}
+
+bool SymtabShndxSection::empty() const {
+ // SHT_SYMTAB can hold symbols with section indices values up to
+ // SHN_LORESERVE. If we need more, we want to use extension SHT_SYMTAB_SHNDX
+ // section. Problem is that we reveal the final section indices a bit too
+ // late, and we do not know them here. For simplicity, we just always create
+ // a .symtab_shndxr section when the amount of output sections is huge.
+ size_t Size = 0;
+ for (BaseCommand *Base : Script->SectionCommands)
+ if (isa<OutputSection>(Base))
+ ++Size;
+ return Size < SHN_LORESERVE;
+}
+
+void SymtabShndxSection::finalizeContents() {
+ getParent()->Link = InX::SymTab->getParent()->SectionIndex;
+}
+
+size_t SymtabShndxSection::getSize() const {
+ return InX::SymTab->getNumSymbols() * 4;
+}
+
// .hash and .gnu.hash sections contain on-disk hash tables that map
// symbol names to their dynamic symbol table indices. Their purpose
// is to help the dynamic linker resolve symbols quickly. If ELF files
@@ -3025,6 +3065,7 @@ RelocationBaseSection *InX::RelaIplt;
StringTableSection *InX::ShStrTab;
StringTableSection *InX::StrTab;
SymbolTableBaseSection *InX::SymTab;
+SymtabShndxSection *InX::SymTabShndx;
template GdbIndexSection *GdbIndexSection::create<ELF32LE>();
template GdbIndexSection *GdbIndexSection::create<ELF32BE>();
Modified: lld/trunk/ELF/SyntheticSections.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/SyntheticSections.h?rev=338247&r1=338246&r2=338247&view=diff
==============================================================================
--- lld/trunk/ELF/SyntheticSections.h (original)
+++ lld/trunk/ELF/SyntheticSections.h Mon Jul 30 05:39:54 2018
@@ -588,6 +588,16 @@ public:
void writeTo(uint8_t *Buf) override;
};
+class SymtabShndxSection final : public SyntheticSection {
+public:
+ SymtabShndxSection();
+
+ void writeTo(uint8_t *Buf) override;
+ size_t getSize() const override;
+ bool empty() const override;
+ void finalizeContents() override;
+};
+
// Outputs GNU Hash section. For detailed explanation see:
// https://blogs.oracle.com/ali/entry/gnu_hash_elf_sections
class GnuHashTableSection final : public SyntheticSection {
@@ -992,6 +1002,7 @@ struct InX {
static StringTableSection *ShStrTab;
static StringTableSection *StrTab;
static SymbolTableBaseSection *SymTab;
+ static SymtabShndxSection* SymTabShndx;
};
template <class ELFT> struct In {
Modified: lld/trunk/ELF/Writer.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=338247&r1=338246&r2=338247&view=diff
==============================================================================
--- lld/trunk/ELF/Writer.cpp (original)
+++ lld/trunk/ELF/Writer.cpp Mon Jul 30 05:39:54 2018
@@ -287,6 +287,7 @@ template <class ELFT> static void create
if (Config->Strip != StripPolicy::All) {
InX::StrTab = make<StringTableSection>(".strtab", false);
InX::SymTab = make<SymbolTableSection<ELFT>>(*InX::StrTab);
+ InX::SymTabShndx = make<SymtabShndxSection>();
}
if (Config->BuildId != BuildIdKind::None) {
@@ -409,6 +410,8 @@ template <class ELFT> static void create
if (InX::SymTab)
Add(InX::SymTab);
+ if (InX::SymTabShndx)
+ Add(InX::SymTabShndx);
Add(InX::ShStrTab);
if (InX::StrTab)
Add(InX::StrTab);
@@ -1639,12 +1642,13 @@ template <class ELFT> void Writer<ELFT>:
// Dynamic section must be the last one in this list and dynamic
// symbol table section (DynSymTab) must be the first one.
applySynthetic(
- {InX::DynSymTab, InX::Bss, InX::BssRelRo, InX::GnuHashTab,
- InX::HashTab, InX::SymTab, InX::ShStrTab, InX::StrTab,
- In<ELFT>::VerDef, InX::DynStrTab, InX::Got, InX::MipsGot,
- InX::IgotPlt, InX::GotPlt, InX::RelaDyn, InX::RelrDyn,
- InX::RelaIplt, InX::RelaPlt, InX::Plt, InX::Iplt,
- InX::EhFrameHdr, In<ELFT>::VerSym, In<ELFT>::VerNeed, InX::Dynamic},
+ {InX::DynSymTab, InX::Bss, InX::BssRelRo, InX::GnuHashTab,
+ InX::HashTab, InX::SymTab, InX::SymTabShndx, InX::ShStrTab,
+ InX::StrTab, In<ELFT>::VerDef, InX::DynStrTab, InX::Got,
+ InX::MipsGot, InX::IgotPlt, InX::GotPlt, InX::RelaDyn,
+ InX::RelrDyn, InX::RelaIplt, InX::RelaPlt, InX::Plt,
+ InX::Iplt, InX::EhFrameHdr, In<ELFT>::VerSym, In<ELFT>::VerNeed,
+ InX::Dynamic},
[](SyntheticSection *SS) { SS->finalizeContents(); });
if (!Script->HasSectionsCommand && !Config->Relocatable)
Modified: lld/trunk/test/ELF/linkerscript/orphan-report.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/linkerscript/orphan-report.s?rev=338247&r1=338246&r2=338247&view=diff
==============================================================================
--- lld/trunk/test/ELF/linkerscript/orphan-report.s (original)
+++ lld/trunk/test/ELF/linkerscript/orphan-report.s Mon Jul 30 05:39:54 2018
@@ -36,6 +36,7 @@
# REPORT-NEXT: <internal>:(.plt) is being placed in '.plt'
# REPORT-NEXT: <internal>:(.eh_frame) is being placed in '.eh_frame'
# REPORT-NEXT: <internal>:(.symtab) is being placed in '.symtab'
+# REPORT-NEXT: <internal>:(.symtab_shndxr) is being placed in '.symtab_shndxr'
# REPORT-NEXT: <internal>:(.shstrtab) is being placed in '.shstrtab'
# REPORT-NEXT: <internal>:(.strtab) is being placed in '.strtab'
Modified: lld/trunk/test/ELF/relocatable-many-sections.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/relocatable-many-sections.s?rev=338247&r1=338246&r2=338247&view=diff
==============================================================================
--- lld/trunk/test/ELF/relocatable-many-sections.s (original)
+++ lld/trunk/test/ELF/relocatable-many-sections.s Mon Jul 30 05:39:54 2018
@@ -1,20 +1,32 @@
# REQUIRES: x86
# RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o %t.o
# RUN: ld.lld -r %t.o -o %t
-# RUN: llvm-readobj -file-headers %t | FileCheck %s
-## Check we are able to emit a valid ELF header when
+## Check we are able to link against relocatable file produced.
+# RUN: ld.lld %t -o %t.out
+
+## Check we emit a valid ELF header when
## sections amount is greater than SHN_LORESERVE.
-# CHECK: ElfHeader {
-# CHECK: SectionHeaderCount: 0 (65541)
-# CHECK-NEXT: StringTableSectionIndex: 65535 (65539)
-
-## Check that 65539 is really the index of .shstrtab section.
-# RUN: llvm-objdump -section-headers -section=.shstrtab %t \
-# RUN: | FileCheck %s --check-prefix=SHSTRTAB
-# SHSTRTAB: Sections:
-# SHSTRTAB-NEXT: Idx Name
-# SHSTRTAB-NEXT: 65539 .shstrtab
+# RUN: llvm-readobj -file-headers %t | FileCheck %s --check-prefix=HDR
+# HDR: ElfHeader {
+# HDR: SectionHeaderCount: 0 (65543)
+# HDR-NEXT: StringTableSectionIndex: 65535 (65541)
+
+## Check that:
+## 1) 65541 is the index of .shstrtab section.
+## 2) .symtab_shndxr is linked with .symtab.
+## 3) .symtab_shndxr entry size and alignment == 4.
+## 4) .symtab_shndxr has size equal to
+## (sizeof(.symtab) / entsize(.symtab)) * entsize(.symtab_shndxr) = 0x4 * 0x180048 / 0x18 == 0x04000c
+# RUN: llvm-readelf -sections -symbols %t | FileCheck %s
+## [Nr] Name Type Address Off Size ES Flg Lk Inf Al
+# CHECK: [65538] .bar
+# CHECK-NEXT: [65539] .symtab SYMTAB 0000000000000000 000040 180078 18 65542 65539 8
+# CHECK-NEXT: [65540] .symtab_shndxr SYMTAB SECTION INDICES 0000000000000000 1800b8 040014 04 65539 0 4
+# CHECK-NEXT: [65541] .shstrtab STRTAB 0000000000000000 1c00cc 0f0035 00 0 0 1
+# CHECK-NEXT: [65542] .strtab STRTAB 0000000000000000 2b0101 00000c 00
+# 5) Check we are able to represent symbol foo with section (.bar) index > 0xFF00 (SHN_LORESERVE).
+# CHECK: GLOBAL DEFAULT 65538 foo
.macro gen_sections4 x
.section a\x
@@ -88,5 +100,10 @@ gen_sections16384 b
gen_sections16384 c
gen_sections16384 d
+.section .bar
+.global foo
+foo:
+
+.section .text, "ax"
.global _start
_start:
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