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

diff --git a/lld/ELF/Arch/Mips.cpp b/lld/ELF/Arch/Mips.cpp
index fcf5aff..d8631b5 100644 (file)
--- a/lld/ELF/Arch/Mips.cpp
+++ b/lld/ELF/Arch/Mips.cpp
@@ -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;

diff --git a/lld/ELF/Arch/PPC.cpp b/lld/ELF/Arch/PPC.cpp
index 6af0df3..20cae0e 100644 (file)
--- a/lld/ELF/Arch/PPC.cpp
+++ b/lld/ELF/Arch/PPC.cpp
@@ -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) {

diff --git a/lld/ELF/Arch/X86.cpp b/lld/ELF/Arch/X86.cpp
index 09c16db..e38fc08 100644 (file)
--- a/lld/ELF/Arch/X86.cpp
+++ b/lld/ELF/Arch/X86.cpp
@@ -46,7 +46,6 @@ public:
 } // namespace
 
 X86::X86() {
-  GotBaseSymOff = -1;
   CopyRel = R_386_COPY;
   GotRel = R_386_GLOB_DAT;
   PltRel = R_386_JUMP_SLOT;

diff --git a/lld/ELF/Arch/X86_64.cpp b/lld/ELF/Arch/X86_64.cpp
index 3db391e..476b16c 100644 (file)
--- a/lld/ELF/Arch/X86_64.cpp
+++ b/lld/ELF/Arch/X86_64.cpp
@@ -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;

diff --git a/lld/ELF/SyntheticSections.cpp b/lld/ELF/SyntheticSections.cpp
index 026c162..be8b8b9 100644 (file)
--- a/lld/ELF/SyntheticSections.cpp
+++ b/lld/ELF/SyntheticSections.cpp
@@ -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()

diff --git a/lld/ELF/SyntheticSections.h b/lld/ELF/SyntheticSections.h
index 855b91d..c96ccb6 100644 (file)
--- a/lld/ELF/SyntheticSections.h
+++ b/lld/ELF/SyntheticSections.h
@@ -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;

diff --git a/lld/ELF/Target.h b/lld/ELF/Target.h
index 5e8cfc7..29c7c45 100644 (file)
--- a/lld/ELF/Target.h
+++ b/lld/ELF/Target.h
@@ -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.

diff --git a/lld/ELF/Writer.cpp b/lld/ELF/Writer.cpp
index ccec4e4..a59e19b 100644 (file)
--- a/lld/ELF/Writer.cpp
+++ b/lld/ELF/Writer.cpp
@@ -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;
   }
 

diff --git a/lld/test/ELF/arm-got-relative.s b/lld/test/ELF/arm-got-relative.s
index cf8b0a6..c64969d 100644 (file)
--- a/lld/test/ELF/arm-got-relative.s
+++ b/lld/test/ELF/arm-got-relative.s
@@ -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

diff --git a/lld/test/ELF/dynamic-got.s b/lld/test/ELF/dynamic-got.s
index 385394b..844e4f4 100644 (file)
--- a/lld/test/ELF/dynamic-got.s
+++ b/lld/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:

diff --git a/lld/test/ELF/global-offset-table-position-aarch64.s b/lld/test/ELF/global-offset-table-position-aarch64.s
index 68bc4a4..8e26913 100644 (file)
--- a/lld/test/ELF/global-offset-table-position-aarch64.s
+++ b/lld/test/ELF/global-offset-table-position-aarch64.s
@@ -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

diff --git a/lld/test/ELF/global-offset-table-position-arm.s b/lld/test/ELF/global-offset-table-position-arm.s
index 19619b2..0538129 100644 (file)
--- a/lld/test/ELF/global-offset-table-position-arm.s
+++ b/lld/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 @@ _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

diff --git a/lld/test/ELF/global-offset-table-position-i386.s b/lld/test/ELF/global-offset-table-position-i386.s
index 9f778e1..8d50b49 100644 (file)
--- a/lld/test/ELF/global-offset-table-position-i386.s
+++ b/lld/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,@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

diff --git a/lld/test/ELF/global-offset-table-position.s b/lld/test/ELF/global-offset-table-position.s
index f1195b2..57fe6c8 100644 (file)
--- a/lld/test/ELF/global-offset-table-position.s
+++ b/lld/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,@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

diff --git a/lld/test/ELF/global_offset_table_shared.s b/lld/test/ELF/global_offset_table_shared.s
index 03af02e..06bd7b3 100644 (file)
--- a/lld/test/ELF/global_offset_table_shared.s
+++ b/lld/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

diff --git a/lld/test/ELF/got32x-i386.s b/lld/test/ELF/got32x-i386.s
index 1311472..17c9a1c 100644 (file)
--- a/lld/test/ELF/got32x-i386.s
+++ b/lld/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

diff --git a/lld/test/ELF/i386-gotpc.s b/lld/test/ELF/i386-gotpc.s
index d2c5ef3..af8380b 100644 (file)
--- a/lld/test/ELF/i386-gotpc.s
+++ b/lld/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