diff options
| -rw-r--r-- | lld/ELF/Writer.cpp | 44 |
1 files changed, 31 insertions, 13 deletions
diff --git a/lld/ELF/Writer.cpp b/lld/ELF/Writer.cpp index 4f764593b6b..8d45f9f598f 100644 --- a/lld/ELF/Writer.cpp +++ b/lld/ELF/Writer.cpp @@ -556,9 +556,11 @@ static bool includeInSymtab(const Symbol &B) { if (!Sec) return true; Sec = Sec->Repl; + // Exclude symbols pointing to garbage-collected sections. if (isa<InputSectionBase>(Sec) && !Sec->Live) return false; + if (auto *S = dyn_cast<MergeInputSection>(Sec)) if (!S->getSectionPiece(D->Value)->Live) return false; @@ -594,11 +596,11 @@ template <class ELFT> void Writer<ELFT>::copyLocalSymbols() { } } +// Create a section symbol for each output section so that we can represent +// relocations that point to the section. If we know that no relocation is +// referring to a section (that happens if the section is a synthetic one), we +// don't create a section symbol for that section. template <class ELFT> void Writer<ELFT>::addSectionSymbols() { - // Create a section symbol for each output section so that we can represent - // relocations that point to the section. If we know that no relocation is - // referring to a section (that happens if the section is a synthetic one), we - // don't create a section symbol for that section. for (BaseCommand *Base : Script->SectionCommands) { auto *Sec = dyn_cast<OutputSection>(Base); if (!Sec) @@ -863,8 +865,10 @@ static unsigned getSectionRank(const OutputSection *Sec) { static bool compareSections(const BaseCommand *ACmd, const BaseCommand *BCmd) { const OutputSection *A = cast<OutputSection>(ACmd); const OutputSection *B = cast<OutputSection>(BCmd); + if (A->SortRank != B->SortRank) return A->SortRank < B->SortRank; + if (!(A->SortRank & RF_NOT_ADDR_SET)) return Config->SectionStartMap.lookup(A->Name) < Config->SectionStartMap.lookup(B->Name); @@ -1110,6 +1114,7 @@ static DenseMap<const InputSectionBase *, int> buildSectionOrder() { } } }; + // We want both global and local symbols. We get the global ones from the // symbol table and iterate the object files for the local ones. for (Symbol *Sym : Symtab->getSymbols()) @@ -1354,10 +1359,12 @@ static bool compareByFilePosition(InputSection *A, InputSection *B) { if (A->kind() == InputSectionBase::Synthetic || B->kind() == InputSectionBase::Synthetic) return A->kind() != InputSectionBase::Synthetic; + InputSection *LA = A->getLinkOrderDep(); InputSection *LB = B->getLinkOrderDep(); OutputSection *AOut = LA->getParent(); OutputSection *BOut = LB->getParent(); + if (AOut != BOut) return AOut->SectionIndex < BOut->SectionIndex; return LA->OutSecOff < LB->OutSecOff; @@ -1404,6 +1411,7 @@ static bool isDuplicateArmExidxSec(InputSection *Prev, InputSection *Cur) { for (const ExidxEntry Entry : Cur->getDataAs<ExidxEntry>()) if (IsExtabRef(Entry.Unwind) || Entry.Unwind != PrevEntry.Unwind) return false; + // All table entries in this .ARM.exidx Section can be merged into the // previous Section. return true; @@ -1435,18 +1443,19 @@ template <class ELFT> void Writer<ELFT>::resolveShfLinkOrder() { assert(Sections.size() >= 2 && "We should create a sentinel section only if there are " "alive regular exidx sections."); + // The last executable section is required to fill the sentinel. // Remember it here so that we don't have to find it again. Sentinel->Highest = Sections[Sections.size() - 2]->getLinkOrderDep(); } + // The EHABI for the Arm Architecture permits consecutive identical + // table entries to be merged. We use a simple implementation that + // removes a .ARM.exidx Input Section if it can be merged into the + // previous one. This does not require any rewriting of InputSection + // contents but misses opportunities for fine grained deduplication + // where only a subset of the InputSection contents can be merged. if (Config->MergeArmExidx) { - // The EHABI for the Arm Architecture permits consecutive identical - // table entries to be merged. We use a simple implementation that - // removes a .ARM.exidx Input Section if it can be merged into the - // previous one. This does not require any rewriting of InputSection - // contents but misses opportunities for fine grained deduplication - // where only a subset of the InputSection contents can be merged. size_t Prev = 0; // The last one is a sentinel entry which should not be removed. for (size_t I = 1; I < Sections.size() - 1; ++I) { @@ -1743,7 +1752,7 @@ template <class ELFT> void Writer<ELFT>::finalizeSections() { // layouts (that are needed to determine if jump targets are in range). maybeAddThunks(); - // createThunks may have added local symbols to the static symbol table + // maybeAddThunks may have added local symbols to the static symbol table. finalizeSynthetic(In.SymTab); // Fill other section headers. The dynamic table is finalized @@ -2012,14 +2021,17 @@ template <class ELFT> void Writer<ELFT>::fixSectionAlignments() { for (const PhdrEntry *P : Phdrs) { if (P->p_type != PT_GNU_RELRO) continue; + if (P->FirstSec) PageAlign(P->FirstSec); + // Find the first section after PT_GNU_RELRO. If it is in a PT_LOAD we // have to align it to a page. auto End = OutputSections.end(); auto I = std::find(OutputSections.begin(), End, P->LastSec); if (I == End || (I + 1) == End) continue; + OutputSection *Cmd = (*(I + 1)); if (needsPtLoad(Cmd)) PageAlign(Cmd); @@ -2090,6 +2102,7 @@ template <class ELFT> void Writer<ELFT>::assignFileOffsets() { Off = setFileOffset(Sec, Off); if (Script->HasSectionsCommand) continue; + // If this is a last section of the last executable segment and that // segment is the last loadable segment, align the offset of the // following section to avoid loading non-segments parts of the file. @@ -2125,19 +2138,23 @@ template <class ELFT> void Writer<ELFT>::setPhdrs() { for (PhdrEntry *P : Phdrs) { OutputSection *First = P->FirstSec; OutputSection *Last = P->LastSec; + if (First) { P->p_filesz = Last->Offset - First->Offset; if (Last->Type != SHT_NOBITS) P->p_filesz += Last->Size; + P->p_memsz = Last->Addr + Last->Size - First->Addr; P->p_offset = First->Offset; P->p_vaddr = First->Addr; + if (!P->HasLMA) P->p_paddr = First->getLMA(); } - if (P->p_type == PT_LOAD) + + if (P->p_type == PT_LOAD) { P->p_align = std::max<uint64_t>(P->p_align, Config->MaxPageSize); - else if (P->p_type == PT_GNU_RELRO) { + } else if (P->p_type == PT_GNU_RELRO) { P->p_align = 1; // The glibc dynamic loader rounds the size down, so we need to round up // to protect the last page. This is a no-op on FreeBSD which always @@ -2294,6 +2311,7 @@ static uint8_t getAbiVersion() { template <class ELFT> void Writer<ELFT>::writeHeader() { uint8_t *Buf = Buffer->getBufferStart(); + // For executable segments, the trap instructions are written before writing // the header. Setting Elf header bytes to zero ensures that any unused bytes // in header are zero-cleared, instead of having trap instructions. |
