[lld] r247925 - [elf2] Combine adjacent compatible OutputSections in PT_LOADs.
Michael Spencer via llvm-commits
llvm-commits at lists.llvm.org
Thu Sep 17 14:23:24 PDT 2015
On Thu, Sep 17, 2015 at 2:05 PM, Rafael Espíndola
<rafael.espindola at gmail.com> wrote:
> On the review thread I wrote:
>
> LGTM on the condition that one extra test is added showing a read
> only section being included in the initial PT_LOAD.
>
> I don't see any such test.
r247947
>
> Also, elf2/dynamic-reloc.s is failing.
r247946
- Michael Spencer
>
>
> On 17 September 2015 at 15:58, Michael J. Spencer via llvm-commits
> <llvm-commits at lists.llvm.org> wrote:
>> Author: mspencer
>> Date: Thu Sep 17 14:58:07 2015
>> New Revision: 247925
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=247925&view=rev
>> Log:
>> [elf2] Combine adjacent compatible OutputSections in PT_LOADs.
>>
>> Added:
>> lld/trunk/test/elf2/program-header-layout.s
>> Modified:
>> lld/trunk/ELF/Writer.cpp
>> lld/trunk/test/elf2/dynamic-reloc.s
>> lld/trunk/test/elf2/relocation.s
>> lld/trunk/test/elf2/shared.s
>>
>> Modified: lld/trunk/ELF/Writer.cpp
>> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=247925&r1=247924&r2=247925&view=diff
>> ==============================================================================
>> --- lld/trunk/ELF/Writer.cpp (original)
>> +++ lld/trunk/ELF/Writer.cpp Thu Sep 17 14:58:07 2015
>> @@ -446,6 +446,57 @@ private:
>> SymbolTable &SymTab;
>> };
>>
>> +static uint32_t convertSectionFlagsToPHDRFlags(uint64_t Flags) {
>> + uint32_t Ret = PF_R;
>> + if (Flags & SHF_WRITE)
>> + Ret |= PF_W;
>> +
>> + if (Flags & SHF_EXECINSTR)
>> + Ret |= PF_X;
>> +
>> + return Ret;
>> +}
>> +
>> +template <bool Is64Bits>
>> +class ProgramHeader {
>> +public:
>> + typedef typename std::conditional<Is64Bits, uint64_t, uint32_t>::type uintX_t;
>> + typedef
>> + typename std::conditional<Is64Bits, Elf64_Phdr, Elf32_Phdr>::type HeaderT;
>> +
>> + ProgramHeader(uintX_t p_type, uintX_t p_flags) {
>> + std::memset(&Header, 0, sizeof(HeaderT));
>> + Header.p_type = p_type;
>> + Header.p_flags = p_flags;
>> + Header.p_align = PageSize;
>> + }
>> +
>> + void setValuesFromSection(OutputSectionBase<Is64Bits> &Sec) {
>> + Header.p_flags = convertSectionFlagsToPHDRFlags(Sec.getFlags());
>> + Header.p_offset = Sec.getFileOff();
>> + Header.p_vaddr = Sec.getVA();
>> + Header.p_paddr = Header.p_vaddr;
>> + Header.p_filesz = Sec.getSize();
>> + Header.p_memsz = Header.p_filesz;
>> + Header.p_align = Sec.getAlign();
>> + }
>> +
>> + template <endianness E>
>> + void writeHeaderTo(typename ELFFile<ELFType<E, Is64Bits>>::Elf_Phdr *PHDR) {
>> + PHDR->p_type = Header.p_type;
>> + PHDR->p_flags = Header.p_flags;
>> + PHDR->p_offset = Header.p_offset;
>> + PHDR->p_vaddr = Header.p_vaddr;
>> + PHDR->p_paddr = Header.p_paddr;
>> + PHDR->p_filesz = Header.p_filesz;
>> + PHDR->p_memsz = Header.p_memsz;
>> + PHDR->p_align = Header.p_align;
>> + }
>> +
>> + HeaderT Header;
>> + bool Closed = false;
>> +};
>> +
>> // The writer writes a SymbolTable result to a file.
>> template <class ELFT> class Writer {
>> public:
>> @@ -487,14 +538,20 @@ private:
>> unsigned getVAStart() const { return Config->Shared ? 0 : VAStart; }
>>
>> std::unique_ptr<llvm::FileOutputBuffer> Buffer;
>> +
>> llvm::SpecificBumpPtrAllocator<OutputSection<ELFT>> CAlloc;
>> std::vector<OutputSectionBase<ELFT::Is64Bits> *> OutputSections;
>> unsigned getNumSections() const { return OutputSections.size() + 1; }
>>
>> + llvm::BumpPtrAllocator PAlloc;
>> + std::vector<ProgramHeader<ELFT::Is64Bits> *> PHDRs;
>> + ProgramHeader<ELFT::Is64Bits> FileHeaderPHDR{PT_LOAD, PF_R};
>> + ProgramHeader<ELFT::Is64Bits> InterpPHDR{PT_INTERP, 0};
>> + ProgramHeader<ELFT::Is64Bits> DynamicPHDR{PT_DYNAMIC, 0};
>> +
>> uintX_t FileSize;
>> uintX_t ProgramHeaderOff;
>> uintX_t SectionHeaderOff;
>> - unsigned NumPhdrs;
>>
>> StringTableSection<ELFT::Is64Bits> StrTabSec = { /*dynamic=*/false };
>> StringTableSection<ELFT::Is64Bits> DynStrSec = { /*dynamic=*/true };
>> @@ -950,12 +1007,13 @@ template <class ELFT> void Writer<ELFT>:
>>
>> template <class ELFT>
>> static bool outputSectionHasPHDR(OutputSectionBase<ELFT::Is64Bits> *Sec) {
>> - return (Sec->getSize() != 0) && (Sec->getFlags() & SHF_ALLOC);
>> + return Sec->getFlags() & SHF_ALLOC;
>> }
>>
>> // Visits all sections to assign incremental, non-overlapping RVAs and
>> // file offsets.
>> template <class ELFT> void Writer<ELFT>::assignAddresses() {
>> + assert(!OutputSections.empty() && "No output sections to layout!");
>> uintX_t VA = getVAStart();
>> uintX_t FileOff = 0;
>>
>> @@ -967,26 +1025,41 @@ template <class ELFT> void Writer<ELFT>:
>> FileOff = RoundUpToAlignment(FileOff, PageSize);
>> VA = RoundUpToAlignment(VA, PageSize);
>>
>> - NumPhdrs = 0;
>> -
>> - // Add a PHDR for PT_INTERP.
>> if (needsInterpSection())
>> - ++NumPhdrs;
>> + PHDRs.push_back(&InterpPHDR);
>>
>> - // Add a PHDR for the elf header and program headers. Some dynamic linkers
>> - // (musl at least) require them to be covered by a PT_LOAD.
>> - ++NumPhdrs;
>> + ProgramHeader<ELFT::Is64Bits> *LastPHDR = &FileHeaderPHDR;
>> + // Create a PHDR for the file header.
>> + PHDRs.push_back(&FileHeaderPHDR);
>> + FileHeaderPHDR.Header.p_vaddr = getVAStart();
>> + FileHeaderPHDR.Header.p_paddr = getVAStart();
>> + FileHeaderPHDR.Header.p_align = PageSize;
>>
>> for (OutputSectionBase<ELFT::Is64Bits> *Sec : OutputSections) {
>> StrTabSec.add(Sec->getName());
>> Sec->finalize();
>>
>> - // Since each output section gets its own PHDR, align each output section to
>> - // a page.
>> - if (outputSectionHasPHDR<ELFT>(Sec)) {
>> - ++NumPhdrs;
>> - VA = RoundUpToAlignment(VA, PageSize);
>> - FileOff = RoundUpToAlignment(FileOff, PageSize);
>> + if (Sec->getSize()) {
>> + uintX_t Flags = convertSectionFlagsToPHDRFlags(Sec->getFlags());
>> + if (LastPHDR->Header.p_flags != Flags ||
>> + !outputSectionHasPHDR<ELFT>(Sec)) {
>> + // Flags changed. End current PHDR and potentially create a new one.
>> + if (!LastPHDR->Closed) {
>> + LastPHDR->Header.p_filesz = FileOff - LastPHDR->Header.p_offset;
>> + LastPHDR->Header.p_memsz = VA - LastPHDR->Header.p_vaddr;
>> + LastPHDR->Closed = true;
>> + }
>> +
>> + if (outputSectionHasPHDR<ELFT>(Sec)) {
>> + LastPHDR = new (PAlloc) ProgramHeader<ELFT::Is64Bits>(PT_LOAD, Flags);
>> + PHDRs.push_back(LastPHDR);
>> + VA = RoundUpToAlignment(VA, PageSize);
>> + FileOff = RoundUpToAlignment(FileOff, PageSize);
>> + LastPHDR->Header.p_offset = FileOff;
>> + LastPHDR->Header.p_vaddr = VA;
>> + LastPHDR->Header.p_paddr = VA;
>> + }
>> + }
>> }
>>
>> uintX_t Align = Sec->getAlign();
>> @@ -1004,7 +1077,7 @@ template <class ELFT> void Writer<ELFT>:
>>
>> // Add a PHDR for the dynamic table.
>> if (needsDynamicSections())
>> - ++NumPhdrs;
>> + PHDRs.push_back(&DynamicPHDR);
>>
>> FileOff += OffsetToAlignment(FileOff, ELFT::Is64Bits ? 8 : 4);
>>
>> @@ -1014,29 +1087,6 @@ template <class ELFT> void Writer<ELFT>:
>> FileSize = FileOff;
>> }
>>
>> -static uint32_t convertSectionFlagsToPHDRFlags(uint64_t Flags) {
>> - uint32_t Ret = PF_R;
>> - if (Flags & SHF_WRITE)
>> - Ret |= PF_W;
>> -
>> - if (Flags & SHF_EXECINSTR)
>> - Ret |= PF_X;
>> -
>> - return Ret;
>> -}
>> -
>> -template <class ELFT>
>> -static void setValuesFromSection(typename ELFFile<ELFT>::Elf_Phdr &P,
>> - OutputSectionBase<ELFT::Is64Bits> &S) {
>> - P.p_flags = convertSectionFlagsToPHDRFlags(S.getFlags());
>> - P.p_offset = S.getFileOff();
>> - P.p_vaddr = S.getVA();
>> - P.p_paddr = P.p_vaddr;
>> - P.p_filesz = S.getSize();
>> - P.p_memsz = P.p_filesz;
>> - P.p_align = S.getAlign();
>> -}
>> -
>> template <class ELFT> void Writer<ELFT>::writeHeader() {
>> uint8_t *Buf = Buffer->getBufferStart();
>> auto *EHdr = reinterpret_cast<Elf_Ehdr *>(Buf);
>> @@ -1065,46 +1115,24 @@ template <class ELFT> void Writer<ELFT>:
>> EHdr->e_shoff = SectionHeaderOff;
>> EHdr->e_ehsize = sizeof(Elf_Ehdr);
>> EHdr->e_phentsize = sizeof(Elf_Phdr);
>> - EHdr->e_phnum = NumPhdrs;
>> + EHdr->e_phnum = PHDRs.size();
>> EHdr->e_shentsize = sizeof(Elf_Shdr);
>> EHdr->e_shnum = getNumSections();
>> EHdr->e_shstrndx = StrTabSec.getSectionIndex();
>>
>> - auto PHdrs = reinterpret_cast<Elf_Phdr *>(Buf + EHdr->e_phoff);
>> - if (needsInterpSection()) {
>> - PHdrs->p_type = PT_INTERP;
>> - setValuesFromSection<ELFT>(*PHdrs, InterpSec);
>> - ++PHdrs;
>> - }
>> -
>> - PHdrs->p_type = PT_LOAD;
>> - PHdrs->p_flags = PF_R;
>> - PHdrs->p_offset = 0;
>> - PHdrs->p_vaddr = getVAStart();
>> - PHdrs->p_paddr = PHdrs->p_vaddr;
>> - PHdrs->p_filesz = ProgramHeaderOff + NumPhdrs * sizeof(Elf_Phdr);
>> - PHdrs->p_memsz = PHdrs->p_filesz;
>> - PHdrs->p_align = PageSize;
>> - ++PHdrs;
>> + // If nothing was merged into the file header PT_LOAD, set the size correctly.
>> + if (FileHeaderPHDR.Header.p_filesz == PageSize)
>> + FileHeaderPHDR.Header.p_filesz = FileHeaderPHDR.Header.p_memsz =
>> + sizeof(Elf_Ehdr) + sizeof(Elf_Phdr) * PHDRs.size();
>>
>> - for (OutputSectionBase<ELFT::Is64Bits> *Sec : OutputSections) {
>> - if (!outputSectionHasPHDR<ELFT>(Sec))
>> - continue;
>> - PHdrs->p_type = PT_LOAD;
>> - PHdrs->p_flags = convertSectionFlagsToPHDRFlags(Sec->getFlags());
>> - PHdrs->p_offset = Sec->getFileOff();
>> - PHdrs->p_vaddr = Sec->getVA();
>> - PHdrs->p_paddr = PHdrs->p_vaddr;
>> - PHdrs->p_filesz = Sec->getType() == SHT_NOBITS ? 0 : Sec->getSize();
>> - PHdrs->p_memsz = Sec->getSize();
>> - PHdrs->p_align = PageSize;
>> - ++PHdrs;
>> - }
>> + if (needsInterpSection())
>> + InterpPHDR.setValuesFromSection(InterpSec);
>> + if (needsDynamicSections())
>> + DynamicPHDR.setValuesFromSection(DynamicSec);
>>
>> - if (needsDynamicSections()) {
>> - PHdrs->p_type = PT_DYNAMIC;
>> - setValuesFromSection<ELFT>(*PHdrs, DynamicSec);
>> - }
>> + auto PHdrs = reinterpret_cast<Elf_Phdr *>(Buf + EHdr->e_phoff);
>> + for (ProgramHeader<ELFT::Is64Bits> *PHDR : PHDRs)
>> + PHDR->template writeHeaderTo<ELFT::TargetEndianness>(PHdrs++);
>>
>> auto SHdrs = reinterpret_cast<Elf_Shdr *>(Buf + EHdr->e_shoff);
>> // First entry is null.
>>
>> Modified: lld/trunk/test/elf2/dynamic-reloc.s
>> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/elf2/dynamic-reloc.s?rev=247925&r1=247924&r2=247925&view=diff
>> ==============================================================================
>> --- lld/trunk/test/elf2/dynamic-reloc.s (original)
>> +++ lld/trunk/test/elf2/dynamic-reloc.s Thu Sep 17 14:58:07 2015
>> @@ -22,7 +22,7 @@
>> // CHECK-NEXT: SHF_ALLOC
>> // CHECK-NEXT: ]
>> // CHECK-NEXT: Address: [[RELAADDR:.*]]
>> -// CHECK-NEXT: Offset: 0x6000
>> +// CHECK-NEXT: Offset: 0x4058
>> // CHECK-NEXT: Size: [[RELASIZE:.*]]
>> // CHECK-NEXT: Link: 4
>> // CHECK-NEXT: Info: 0
>>
>> Added: lld/trunk/test/elf2/program-header-layout.s
>> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/elf2/program-header-layout.s?rev=247925&view=auto
>> ==============================================================================
>> --- lld/trunk/test/elf2/program-header-layout.s (added)
>> +++ lld/trunk/test/elf2/program-header-layout.s Thu Sep 17 14:58:07 2015
>> @@ -0,0 +1,46 @@
>> +# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
>> +# RUN: lld -flavor gnu2 %t -o %t2
>> +# RUN: llvm-readobj -program-headers %t2 | FileCheck %s
>> +# REQUIRES: x86
>> +
>> +# Check that different output sections with the same flags are merged into a
>> +# single Read/Write PT_LOAD.
>> +
>> +.section .r,"a"
>> +.globl _start
>> +_start:
>> +.quad 0
>> +
>> +.section .a,"aw"
>> +.quad 1
>> +
>> +.section .b,"aw"
>> +.quad 2
>> +
>> +# CHECK: ProgramHeaders [
>> +# CHECK-NEXT: ProgramHeader {
>> +# CHECK-NEXT: Type: PT_LOAD
>> +# CHECK-NEXT: Offset: 0x0
>> +# CHECK-NEXT: VirtualAddress:
>> +# CHECK-NEXT: PhysicalAddress:
>> +# CHECK-NEXT: FileSize:
>> +# CHECK-NEXT: MemSize:
>> +# CHECK-NEXT: Flags [
>> +# CHECK-NEXT: PF_R
>> +# CHECK-NEXT: ]
>> +# CHECK-NEXT: Alignment:
>> +# CHECK-NEXT: }
>> +# CHECK-NEXT: ProgramHeader {
>> +# CHECK-NEXT: Type: PT_LOAD
>> +# CHECK-NEXT: Offset:
>> +# CHECK-NEXT: VirtualAddress:
>> +# CHECK-NEXT: PhysicalAddress:
>> +# CHECK-NEXT: FileSize: 16
>> +# CHECK-NEXT: MemSize: 16
>> +# CHECK-NEXT: Flags [
>> +# CHECK-NEXT: PF_R
>> +# CHECK-NEXT: PF_W
>> +# CHECK-NEXT: ]
>> +# CHECK-NEXT: Alignment:
>> +# CHECK-NEXT: }
>> +# CHECK-NEXT: ]
>>
>> Modified: lld/trunk/test/elf2/relocation.s
>> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/elf2/relocation.s?rev=247925&r1=247924&r2=247925&view=diff
>> ==============================================================================
>> --- lld/trunk/test/elf2/relocation.s (original)
>> +++ lld/trunk/test/elf2/relocation.s Thu Sep 17 14:58:07 2015
>> @@ -33,7 +33,7 @@ R_X86_64_32:
>> // constants in hex.
>> // CHECK: Disassembly of section .text2:
>> // CHECK-NEXT: R_X86_64_32:
>> -// CHECK-NEXT: 12000: {{.*}} movl $73728, %edx
>> +// CHECK-NEXT: 1100c: {{.*}} movl $69644, %edx
>>
>> .section .R_X86_64_32S,"ax", at progbits
>> .global R_X86_64_32S
>> @@ -50,4 +50,4 @@ R_X86_64_64:
>> .quad R_X86_64_64
>>
>> // CHECK: Contents of section .R_X86_64_64:
>> -// CHECK-NEXT: 14000 00400100 00000000
>> +// CHECK-NEXT: 12000 00200100 00000000
>>
>> Modified: lld/trunk/test/elf2/shared.s
>> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/elf2/shared.s?rev=247925&r1=247924&r2=247925&view=diff
>> ==============================================================================
>> --- lld/trunk/test/elf2/shared.s (original)
>> +++ lld/trunk/test/elf2/shared.s Thu Sep 17 14:58:07 2015
>> @@ -12,7 +12,7 @@
>> // SO-NEXT: Flags [
>> // SO-NEXT: ]
>> // SO-NEXT: Address:
>> -// SO-NEXT: Offset: 0x400C
>> +// SO-NEXT: Offset: 0x300C
>> // SO-NEXT: Size:
>> // SO-NEXT: Link:
>> // SO-NEXT: Info:
>> @@ -44,7 +44,7 @@
>> // CHECK-NEXT: SHF_ALLOC
>> // CHECK-NEXT: ]
>> // CHECK-NEXT: Address: [[DYNSYMADDR:.*]]
>> -// CHECK-NEXT: Offset: 0x3000
>> +// CHECK-NEXT: Offset: 0x201C
>> // CHECK-NEXT: Size: 48
>> // CHECK-NEXT: Link: [[DYNSTR:.*]]
>> // CHECK-NEXT: Info: 1
>>
>>
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