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For most Targets the _GLOBAL_OFFSET_TABLE_ symbol is expected to be at 

the start of the .got.plt section so that _GLOBAL_OFFSET_TABLE_[0] =
reserved value that is by convention the address of the dynamic section.
Previously we had defined _GLOBAL_OFFSET_TABLE_ as either the start or end
of the .got section with the intention that the .got.plt section would
follow the .got. However this does not always hold with the current
default section ordering so _GLOBAL_OFFSET_TABLE_[0] may not be consistent
with the reserved first entry of the .got.plt.

X86, X86_64, Arm and AArch64 will use the .got.plt. Mips and Power use .got

Fixes PR36555

Differential Revision: https://reviews.llvm.org/D44259

llvm-svn: 327248
This commit is contained in:
Peter Smith 2018-03-11 20:58:18 +00:00
parent d09cc9c62c
commit 18aa0be36e
17 changed files with 85 additions and 42 deletions
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1
lld/ELF/Arch/Mips.cpp
View File

@ -50,6 +50,7 @@ template <class ELFT> MIPS<ELFT>::MIPS() {
DefaultMaxPageSize = 65536;
GotEntrySize = sizeof(typename ELFT::uint);
GotPltEntrySize = sizeof(typename ELFT::uint);
GotBaseSymInGotPlt = false;
PltEntrySize = 16;
PltHeaderSize = 32;
CopyRel = R_MIPS_COPY;

7
lld/ELF/Arch/PPC.cpp
View File

@ -21,13 +21,18 @@ using namespace lld::elf;
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) {

1
lld/ELF/Arch/X86.cpp
View File

@ -46,7 +46,6 @@ public:
} // namespace
X86::X86() {
GotBaseSymOff = -1;
CopyRel = R_386_COPY;
GotRel = R_386_GLOB_DAT;
PltRel = R_386_JUMP_SLOT;

1
lld/ELF/Arch/X86_64.cpp
View File

@ -51,7 +51,6 @@ private:
} // 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;

13
lld/ELF/SyntheticSections.cpp
View File

@ -626,8 +626,9 @@ void GotSection::finalizeContents() { Size = NumEntries * Config->Wordsize; }
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) {
@ -898,6 +899,14 @@ void GotPltSection::writeTo(uint8_t *Buf) {
}
}
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()

2
lld/ELF/SyntheticSections.h
View File

@ -269,7 +269,7 @@ public:
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;

5
lld/ELF/Target.h
View File

@ -71,9 +71,10 @@ public:
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.

11
lld/ELF/Writer.cpp
View File

@ -868,11 +868,12 @@ void Writer<ELFT>::forEachRelSec(std::function<void(InputSectionBase &)> Fn) {
// 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;
}

10
lld/test/ELF/arm-got-relative.s
View File

@ -28,17 +28,17 @@ function:
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:
@ -47,7 +47,7 @@ function:
// 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

27
lld/test/ELF/dynamic-got.s
View File

@ -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:

4
lld/test/ELF/global-offset-table-position-aarch64.s
View File

@ -20,11 +20,11 @@ _start:
.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

7
lld/test/ELF/global-offset-table-position-arm.s
View File

@ -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 @@ _start:
.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

7
lld/test/ELF/global-offset-table-position-i386.s
View File

@ -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,@object
.comm a,4,4
@ -21,11 +22,11 @@ addl $_GLOBAL_OFFSET_TABLE_, %eax
calll f@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

7
lld/test/ELF/global-offset-table-position.s
View File

@ -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,@object
.comm a,4,4
@ -21,11 +22,11 @@ callq f@PLT
.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

4
lld/test/ELF/global_offset_table_shared.s
View File

@ -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

6
lld/test/ELF/got32x-i386.s
View File

@ -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

14
lld/test/ELF/i386-gotpc.s
View File

@ -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