[PATCH] D44259: [LLD][ELF] Use start of .got.plt as the location for _GLOBAL_OFFSET_TABLE_
Rafael Avila de Espindola via llvm-commits
llvm-commits at lists.llvm.org
Fri Mar 9 10:02:56 PST 2018
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 @@
>
> ## 73728 == 0x12000 == ADDR(.got)
> # CHECK: _start:
> -# CHECK-NEXT: 11001: 8b 05 {{.*}} movl 73728, %eax
> -# CHECK-NEXT: 11007: 8b 1d {{.*}} movl 73728, %ebx
> +# CHECK-NEXT: 11001: 8b 05 {{.*}} movl 77824, %eax
> +# CHECK-NEXT: 11007: 8b 1d {{.*}} movl 77824, %ebx
> # CHECK-NEXT: 1100d: 8b 80 {{.*}} movl -4(%eax), %eax
> # CHECK-NEXT: 11013: 8b 83 {{.*}} movl -4(%ebx), %eax
> # CHECK: Sections:
> # CHECK: Name Size Address
> -# CHECK: .got 00000004 0000000000012000
> +# CHECK: .got 00000004 0000000000013000
>
> # RUN: not ld.lld %S/Inputs/i386-got32x-baseless.elf -o %t1 -pie 2>&1 | \
> # 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;
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