[PATCH] D44259: [LLD][ELF] Use start of .got.plt as the location for _GLOBAL_OFFSET_TABLE_
Rafael Ávila de Espíndola via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Fri Mar 9 10:03:07 PST 2018
rafael added a comment.
LGTM
Peter Smith via Phabricator <reviews at reviews.llvm.org> writes:
> peter.smith updated this revision to Diff 137715.
> peter.smith added a comment.
>
> Thanks for the comment, and apologies for my misreading of the binutils source. I've updated the patch to keep Mips as it was previously.
>
> https://reviews.llvm.org/D44259
>
> Files:
>
> ELF/Arch/Mips.cpp
> ELF/Arch/PPC.cpp
> ELF/Arch/X86.cpp
> ELF/Arch/X86_64.cpp
> ELF/SyntheticSections.cpp
> ELF/SyntheticSections.h
> ELF/Target.h
> ELF/Writer.cpp
> test/ELF/arm-got-relative.s
> test/ELF/dynamic-got.s
> test/ELF/global-offset-table-position-aarch64.s
> test/ELF/global-offset-table-position-arm.s
> test/ELF/global-offset-table-position-i386.s
> test/ELF/global-offset-table-position.s
> test/ELF/global_offset_table_shared.s
> test/ELF/got32x-i386.s
> test/ELF/i386-gotpc.s
>
> Index: test/ELF/i386-gotpc.s
> ===================================================================
>
> - test/ELF/i386-gotpc.s +++ test/ELF/i386-gotpc.s @@ -6,15 +6,23 @@
>
> movl $_GLOBAL_OFFSET_TABLE_, %eax
>
> +// CHECK: Name: .got.plt +// CHECK-NEXT: Type: SHT_PROGBITS +// CHECK-NEXT: Flags [ +// CHECK-NEXT: SHF_ALLOC +// CHECK-NEXT: SHF_WRITE +// CHECK-NEXT: ] +// CHECK-NEXT: Address: 0x2000 + // CHECK: Name: .got // CHECK-NEXT: Type: SHT_PROGBITS // CHECK-NEXT: Flags [ // CHECK-NEXT: SHF_ALLOC // CHECK-NEXT: SHF_WRITE // CHECK-NEXT: ] -// CHECK-NEXT: Address: 0x2030 +// CHECK-NEXT: Address: 0x3030
>
> // DISASM: Disassembly of section .text: // DISASM-NEXT: .text: -// DISASM-NEXT: 1000: {{.*}} movl $4144, %eax -// 0x2030 - 0x1000 = 4144 +// DISASM-NEXT: 1000: {{.*}} movl $8240, %eax +// 0x3030 - 0x1000 = 0x2030 Index: test/ELF/got32x-i386.s ===================================================================
> - test/ELF/got32x-i386.s +++ test/ELF/got32x-i386.s @@ -33,13 +33,13 @@
> 1. 73728 == 0x12000 == ADDR(.got)
> 2. CHECK: _start:
> 3. CHECK-NEXT: 11001: 8b 05 {{.*}} movl 73728, %eax
> 4. CHECK-NEXT: 11007: 8b 1d {{.*}} movl 73728, %ebx +# CHECK-NEXT: 11001: 8b 05 {{.*}} movl 77824, %eax +# CHECK-NEXT: 11007: 8b 1d {{.*}} movl 77824, %ebx
> 5. CHECK-NEXT: 1100d: 8b 80 {{.*}} movl -4(%eax), %eax
> 6. CHECK-NEXT: 11013: 8b 83 {{.*}} movl -4(%ebx), %eax
> 7. CHECK: Sections:
> 8. CHECK: Name Size Address
> 9. CHECK: .got 00000004 0000000000012000 +# CHECK: .got 00000004 0000000000013000
> 10. RUN: not ld.lld %S/Inputs/i386-got32x-baseless.elf -o %t1 -pie 2>&1 | \
> 11. RUN: FileCheck %s --check-prefix=ERR Index: test/ELF/global_offset_table_shared.s ===================================================================
> - test/ELF/global_offset_table_shared.s +++ test/ELF/global_offset_table_shared.s @@ -4,11 +4,11 @@ .long _GLOBAL_OFFSET_TABLE_ - .
>
> // CHECK: Name: _GLOBAL_OFFSET_TABLE_ -// CHECK-NEXT: Value: 0x2060 +// CHECK-NEXT: Value: 0x2000 // CHECK-NEXT: Size: 0 // CHECK-NEXT: Binding: Local // CHECK-NEXT: Type: None // CHECK-NEXT: Other [ (0x2) // CHECK-NEXT: STV_HIDDEN (0x2) // CHECK-NEXT: ] -// CHECK-NEXT: Section: .got +// CHECK-NEXT: Section: .got.plt Index: test/ELF/global-offset-table-position.s ===================================================================
> - test/ELF/global-offset-table-position.s +++ test/ELF/global-offset-table-position.s @@ -3,7 +3,8 @@ // RUN: llvm-readobj -t %t2 | FileCheck %s // REQUIRES: x86
>
> -// The X86_64 _GLOBAL_OFFSET_TABLE_ is defined at the end of the .got section. +// The X86_64 _GLOBAL_OFFSET_TABLE_ is defined at the start of the .got.plt +// section. .globl a .type a, at object .comm a,4,4 @@ -21,11 +22,11 @@ .long _GLOBAL_OFFSET_TABLE_ - .
>
> // CHECK: Name: _GLOBAL_OFFSET_TABLE_ -// CHECK-NEXT: Value: 0x30D8 +// CHECK-NEXT: Value: 0x2008 // CHECK-NEXT: Size: 0 // CHECK-NEXT: Binding: Local // CHECK-NEXT: Type: None (0x0) // CHECK-NEXT: Other [ // CHECK-NEXT: STV_HIDDEN // CHECK-NEXT: ] -// CHECK-NEXT: Section: .got +// CHECK-NEXT: Section: .got.plt Index: test/ELF/global-offset-table-position-i386.s ===================================================================
> - test/ELF/global-offset-table-position-i386.s +++ test/ELF/global-offset-table-position-i386.s @@ -3,7 +3,8 @@ // RUN: llvm-readobj -t %t2 | FileCheck %s // REQUIRES: x86
>
> -// The X86 _GLOBAL_OFFSET_TABLE_ is defined at the end of the .got section. +// The X86 _GLOBAL_OFFSET_TABLE_ is defined at the start of the .got.plt +// section. .globl a .type a, at object .comm a,4,4 @@ -21,11 +22,11 @@ calll f at PLT
>
> // CHECK: Name: _GLOBAL_OFFSET_TABLE_ (1) -// CHECK-NEXT: Value: 0x306C +// CHECK-NEXT: Value: 0x2000 // CHECK-NEXT: Size: 0 // CHECK-NEXT: Binding: Local (0x0) // CHECK-NEXT: Type: None (0x0) // CHECK-NEXT: Other [ (0x2) // CHECK-NEXT: STV_HIDDEN (0x2) // CHECK-NEXT: ] -// CHECK-NEXT: Section: .got (0xA) +// CHECK-NEXT: Section: .got.plt Index: test/ELF/global-offset-table-position-arm.s ===================================================================
> - test/ELF/global-offset-table-position-arm.s +++ test/ELF/global-offset-table-position-arm.s @@ -3,7 +3,8 @@ // RUN: llvm-readobj -t %t2 | FileCheck %s // REQUIRES: arm
>
> -// The ARM _GLOBAL_OFFSET_TABLE_ should be defined at the start of the .got +// The ARM _GLOBAL_OFFSET_TABLE_ should be defined at the start of the +// .got.plt section. .globl a .type a,%object .comm a,4,4 @@ -25,11 +26,11 @@ .data
>
> // CHECK: Name: _GLOBAL_OFFSET_TABLE_ -// CHECK-NEXT: Value: 0x3068 +// CHECK-NEXT: Value: 0x2000 // CHECK-NEXT: Size: 0 // CHECK-NEXT: Binding: Local // CHECK-NEXT: Type: None // CHECK-NEXT: Other [ (0x2) // CHECK-NEXT: STV_HIDDEN (0x2) // CHECK-NEXT: ] -// CHECK-NEXT: Section: .got +// CHECK-NEXT: Section: .got.plt Index: test/ELF/global-offset-table-position-aarch64.s ===================================================================
> - test/ELF/global-offset-table-position-aarch64.s +++ test/ELF/global-offset-table-position-aarch64.s @@ -20,11 +20,11 @@ .long _GLOBAL_OFFSET_TABLE_ - .
>
> // CHECK: Name: _GLOBAL_OFFSET_TABLE_ (11) -// CHECK-NEXT: Value: 0x30090 +// CHECK-NEXT: Value: 0x20008 // CHECK-NEXT: Size: 0 // CHECK-NEXT: Binding: Local (0x0) // CHECK-NEXT: Type: None (0x0) // CHECK-NEXT: Other [ (0x2) // CHECK-NEXT: STV_HIDDEN (0x2) // CHECK-NEXT: ] -// CHECK-NEXT: Section: .got +// CHECK-NEXT: Section: .got.plt Index: test/ELF/dynamic-got.s ===================================================================
> - test/ELF/dynamic-got.s +++ test/ELF/dynamic-got.s @@ -3,6 +3,23 @@ // RUN: ld.lld --hash-style=sysv %t.o -o %t.so -shared // RUN: llvm-readobj -s -l -section-data -r %t.so | FileCheck %s
>
> +// CHECK: Name: .got.plt +// CHECK-NEXT: Type: SHT_PROGBITS +// CHECK-NEXT: Flags [ +// CHECK-NEXT: SHF_ALLOC +// CHECK-NEXT: SHF_WRITE +// CHECK-NEXT: ] +// CHECK-NEXT: Address: +// CHECK-NEXT: Offset: +// CHECK-NEXT: Size: +// CHECK-NEXT: Link: +// CHECK-NEXT: Info: +// CHECK-NEXT: AddressAlignment: +// CHECK-NEXT: EntrySize: +// CHECK-NEXT: SectionData ( +// CHECK-NEXT: 0000: 00300000 00000000 00000000 +// CHECK-NEXT: ) + // CHECK: Name: .got // CHECK-NEXT: Type: SHT_PROGBITS // CHECK-NEXT: Flags [ @@ -17,19 +34,19 @@ // CHECK-NEXT: AddressAlignment: // CHECK-NEXT: EntrySize: // CHECK-NEXT: SectionData ( -// CHECK-NEXT: 0000: 00200000 | +// CHECK-NEXT: 0000: 00300000 // CHECK-NEXT: )
>
> // CHECK: Relocations [ // CHECK-NEXT: Section ({{.*}}) .rel.dyn { -// CHECK-NEXT: 0x2050 R_386_RELATIVE - 0x0 +// CHECK-NEXT: 0x3050 R_386_RELATIVE - 0x0 // CHECK-NEXT: } // CHECK-NEXT: ]
>
> // CHECK: Type: PT_DYNAMIC -// CHECK-NEXT: Offset: 0x2000 -// CHECK-NEXT: VirtualAddress: 0x2000 -// CHECK-NEXT: PhysicalAddress: 0x2000 +// CHECK-NEXT: Offset: 0x3000 +// CHECK-NEXT: VirtualAddress: 0x3000 +// CHECK-NEXT: PhysicalAddress: 0x3000
>
> calll .L0$pb .L0$pb: Index: test/ELF/arm-got-relative.s ===================================================================
> - test/ELF/arm-got-relative.s +++ test/ELF/arm-got-relative.s @@ -28,26 +28,26 @@ bx lr
>
> // CHECK: Dynamic Relocations { -// CHECK-NEXT: 0x2048 R_ARM_GLOB_DAT function 0x0 +// CHECK-NEXT: 0x3048 R_ARM_GLOB_DAT function 0x0
>
> // CHECK: Name: _GLOBAL_OFFSET_TABLE_ -// CHECK-NEXT: Value: 0x2048 +// CHECK-NEXT: Value: 0x2000 // CHECK-NEXT: Size: // CHECK-NEXT: Binding: Local // CHECK-NEXT: Type: None // CHECK-NEXT: Other [ // CHECK-NEXT: STV_HIDDEN // CHECK-NEXT: ] -// CHECK-NEXT: Section: .got +// CHECK-NEXT: Section: .got.plt
>
> // CODE: Disassembly of section .text: // CODE-NEXT: _start: // CODE-NEXT: 1000: 08 30 9f e5 ldr r3, [pc, #8] // CODE-NEXT: 1004: 08 20 9f e5 ldr r2, [pc, #8] // CODE-NEXT: 1008: 03 00 8f e0 add r0, pc, r3 // CODE-NEXT: 100c: 1e ff 2f e1 bx lr // CODE:$d.1: -// (_GLOBAL_OFFSET_TABLE_ = 0x2048) - (0x1008 + 8) 0x1038 -// CODE-NEXT: 1010: 38 10 00 00 +// (_GLOBAL_OFFSET_TABLE_ = 0x2000) - (0x1008 + 8) = 0xff0 +// CODE-NEXT: 1010: f0 0f 00 00 // (Got(function) - GotBase = 0x0 // CODE-NEXT: 1014: 00 00 00 00 Index: ELF/Writer.cpp ===================================================================
> - ELF/Writer.cpp +++ ELF/Writer.cpp @@ -868,11 +868,12 @@ // defining these symbols explicitly in the linker script. template <class ELFT> void Writer<ELFT>::setReservedSymbolSections() { if (ElfSym::GlobalOffsetTable) {
> - // The _GLOBAL_OFFSET_TABLE_ symbol is defined by target convention to
> - // be at some offset from the base of the .got section, usually 0 or the end
> - // of the .got
> - InputSection *GotSection = InX::MipsGot ? cast<InputSection>(InX::MipsGot)
> - : cast<InputSection>(InX::Got); + // The _GLOBAL_OFFSET_TABLE_ symbol is defined by target convention usually + // to the start of the .got or .got.plt section. + InputSection *GotSection = InX::GotPlt; + if (!Target->GotBaseSymInGotPlt) + GotSection = InX::MipsGot ? cast<InputSection>(InX::MipsGot) + : cast<InputSection>(InX::Got); ElfSym::GlobalOffsetTable->Section = GotSection; }
>
> Index: ELF/Target.h ===================================================================
> - ELF/Target.h +++ ELF/Target.h @@ -71,9 +71,10 @@
>
> uint64_t getImageBase();
> - // Offset of _GLOBAL_OFFSET_TABLE_ from base of .got section. Use -1 for
> - // end of .got + // Offset of _GLOBAL_OFFSET_TABLE_ from base of .got or .got.plt section. uint64_t GotBaseSymOff = 0; + // True if _GLOBAL_OFFSET_TABLE_ is relative to .got.plt, false if .got. + bool GotBaseSymInGotPlt = true;
>
> // On systems with range extensions we place collections of Thunks at // regular spacings that enable the majority of branches reach the Thunks. Index: ELF/SyntheticSections.h ===================================================================
> - ELF/SyntheticSections.h +++ ELF/SyntheticSections.h @@ -269,7 +269,7 @@ void addEntry(Symbol &Sym); size_t getSize() const override; void writeTo(uint8_t *Buf) override;
> - bool empty() const override { return Entries.empty(); } + bool empty() const override;
>
> private: std::vector<const Symbol *> Entries; Index: ELF/SyntheticSections.cpp ===================================================================
> - ELF/SyntheticSections.cpp +++ ELF/SyntheticSections.cpp @@ -628,8 +628,9 @@ bool GotSection::empty() const { // We need to emit a GOT even if it's empty if there's a relocation that is // relative to GOT(such as GOTOFFREL) or there's a symbol that points to a GOT
> - // (i.e. _GLOBAL_OFFSET_TABLE_).
> - return NumEntries == 0 && !HasGotOffRel && !ElfSym::GlobalOffsetTable; + // (i.e. _GLOBAL_OFFSET_TABLE_) that the target defines relative to the .got. + return NumEntries == 0 && !HasGotOffRel && + !(ElfSym::GlobalOffsetTable && !Target->GotBaseSymInGotPlt); }
>
> void GotSection::writeTo(uint8_t *Buf) { @@ -900,6 +901,14 @@ } }
>
> +bool GotPltSection::empty() const { + // We need to emit a GOT.PLT even if it's empty if there's a symbol that + // references the _GLOBAL_OFFSET_TABLE_ and the Target defines the symbol + // relative to the .got.plt section. + return Entries.empty() && + !(ElfSym::GlobalOffsetTable && Target->GotBaseSymInGotPlt); +} + // On ARM the IgotPltSection is part of the GotSection, on other Targets it is // part of the .got.plt IgotPltSection::IgotPltSection() Index: ELF/Arch/X86_64.cpp ===================================================================
> - ELF/Arch/X86_64.cpp +++ ELF/Arch/X86_64.cpp @@ -51,7 +51,6 @@ } // namespace
>
> template <class ELFT> X86_64<ELFT>::X86_64() {
> - GotBaseSymOff = -1; CopyRel = R_X86_64_COPY; GotRel = R_X86_64_GLOB_DAT; PltRel = R_X86_64_JUMP_SLOT; Index: ELF/Arch/X86.cpp ===================================================================
> - ELF/Arch/X86.cpp +++ ELF/Arch/X86.cpp @@ -46,7 +46,6 @@ } // namespace
>
> X86::X86() {
> - GotBaseSymOff = -1; CopyRel = R_386_COPY; GotRel = R_386_GLOB_DAT; PltRel = R_386_JUMP_SLOT; Index: ELF/Arch/PPC.cpp ===================================================================
> - ELF/Arch/PPC.cpp +++ ELF/Arch/PPC.cpp @@ -21,13 +21,18 @@ namespace { class PPC final : public TargetInfo { public:
> - PPC() { GotBaseSymOff = 0x8000; } + PPC(); void relocateOne(uint8_t *Loc, RelType Type, uint64_t Val) const override; RelExpr getRelExpr(RelType Type, const Symbol &S, const uint8_t *Loc) const override; }; } // namespace
>
> +PPC::PPC() { + GotBaseSymOff = 0x8000; + GotBaseSymInGotPlt = false; +} + RelExpr PPC::getRelExpr(RelType Type, const Symbol &S, const uint8_t *Loc) const { switch (Type) { Index: ELF/Arch/Mips.cpp ===================================================================
> - ELF/Arch/Mips.cpp +++ ELF/Arch/Mips.cpp @@ -50,6 +50,7 @@ DefaultMaxPageSize = 65536; GotEntrySize = sizeof(typename ELFT::uint); GotPltEntrySize = sizeof(typename ELFT::uint); + GotBaseSymInGotPlt = false; PltEntrySize = 16; PltHeaderSize = 32; CopyRel = R_MIPS_COPY;
https://reviews.llvm.org/D44259
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