[ELF][PPC32] Implement IPLT code sequence for non-preemptible IFUNC

[MaskRay]

Summary

Similar to D71509 (EM_PPC64), on EM_PPC, the IPLT code sequence should
be similar to a PLT call stub. Unlike EM_PPC64, EM_PPC -msecure-plt has
small/large PIC model differences.

• -fpic/-fpie: R_PPC_PLTREL24 r_addend=0. The call stub loads an address relative to _GLOBAL_OFFSET_TABLE_.
• -fPIC/-fPIE: R_PPC_PLTREL24 r_addend=0x8000. (A partial linked object file may have an addend larger than 0x8000.) The call stub loads an address relative to .got2+0x8000.

Just assume large PIC model for now. This patch makes:

// clang -fuse-ld=lld -fno-pie -no-pie a.c
// clang -fuse-ld=lld -fPIE -pie a.c
#include <stdio.h>
static void impl(void) { puts("meow"); }
void thefunc(void) __attribute__((ifunc("resolver")));
void *resolver(void) { return &impl; }
int main(void) {
  thefunc();
  void (*theptr)(void) = &thefunc;
  theptr();
}

work. -fpie will crash.

[MaskRay]

Make -fPIE -pie work

[MaskRay]

Rebase

[MaskRay]

Properly rebase on top of D71509

[MaskRay]

Add tests

lld/ELF/Arch/PPC.cpp

 //===- PPC.cpp ------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "OutputSections.h"
 #include "Symbols.h"
 #include "SyntheticSections.h"
 #include "Target.h"
+#include "Thunks.h"
 #include "lld/Common/ErrorHandler.h"
 #include "llvm/Support/Endian.h"
 
 using namespace llvm;
 using namespace llvm::support::endian;
 using namespace llvm::ELF;
 
 namespace lld {
public:
   void writeGotHeader(uint8_t *buf) const override;
   void writePltHeader(uint8_t *buf) const override {
     llvm_unreachable("should call writePPC32GlinkSection() instead");
   }
   void writePlt(uint8_t *buf, const Symbol &sym,
                 uint64_t pltEntryAddr) const override {
     llvm_unreachable("should call writePPC32GlinkSection() instead");
   }
+  void writeIplt(uint8_t *buf, const Symbol &sym,
+                 uint64_t pltEntryAddr) const override;
   void writeGotPlt(uint8_t *buf, const Symbol &s) const override;
   bool needsThunk(RelExpr expr, RelType relocType, const InputFile *file,
                   uint64_t branchAddr, const Symbol &s,
                   int64_t a) const override;
   uint32_t getThunkSectionSpacing() const override;
   bool inBranchRange(RelType type, uint64_t src, uint64_t dst) const override;
   void relocateOne(uint8_t *loc, RelType type, uint64_t val) const override;
   RelExpr adjustRelaxExpr(RelType type, const uint8_t *data,
PPC::PPC() {
   relativeRel = R_PPC_RELATIVE;
   iRelativeRel = R_PPC_IRELATIVE;
   symbolicRel = R_PPC_ADDR32;
   gotBaseSymInGotPlt = false;
   gotHeaderEntriesNum = 3;
   gotPltHeaderEntriesNum = 0;
   pltHeaderSize = 64; // size of PLTresolve in .glink
   pltEntrySize = 4;
-  ipltEntrySize = 4;
+  ipltEntrySize = 16;
 
   needsThunks = true;
 
   tlsModuleIndexRel = R_PPC_DTPMOD32;
   tlsOffsetRel = R_PPC_DTPREL32;
   tlsGotRel = R_PPC_TPREL32;
 
   defaultMaxPageSize = 65536;
   defaultImageBase = 0x10000000;
 
   write32(trapInstr.data(), 0x7fe00008);
 }
 
+void PPC::writeIplt(uint8_t *buf, const Symbol &sym,
+                    uint64_t /*pltEntryAddr*/) const {
+  // In -pie or -shared mode, assume r30 points to .got2+0x8000, and use a
+  // .got2.plt_pic32. thunk.
+  writePPC32PltCallStub(buf, sym.getGotPltVA(), sym.file, 0x8000);
+}
+
 void PPC::writeGotHeader(uint8_t *buf) const {
   // _GLOBAL_OFFSET_TABLE_[0] = _DYNAMIC
   // glibc stores _dl_runtime_resolve in _GLOBAL_OFFSET_TABLE_[1],
   // link_map in _GLOBAL_OFFSET_TABLE_[2].
   write32(buf, mainPart->dynamic->getVA());
 }
 
 void PPC::writeGotPlt(uint8_t *buf, const Symbol &s) const {

lld/ELF/Thunks.h

 //===- Thunks.h --------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLD_ELF_THUNKS_H
 #define LLD_ELF_THUNKS_H
 
 #include "Relocations.h"
 
 namespace lld {
 namespace elf {
 class Defined;
+class InputFile;
 class Symbol;
 class ThunkSection;
 // Class to describe an instance of a Thunk.
 // A Thunk is a code-sequence inserted by the linker in between a caller and
 // the callee. The relocation to the callee is redirected to the Thunk, which
 // after executing transfers control to the callee. Typical uses of Thunks
 // include transferring control from non-pi to pi and changing state on
 // targets like ARM.
public:
   // typical code section alignment.
   uint32_t alignment = 4;
 };
 
 // For a Relocation to symbol S create a Thunk to be added to a synthetic
 // ThunkSection.
 Thunk *addThunk(const InputSection &isec, Relocation &rel);
 
+void writePPC32PltCallStub(uint8_t *buf, uint64_t gotPltVA,
+                           const InputFile *file, int64_t addend);
 void writePPC64LoadAndBranch(uint8_t *buf, int64_t offset);
 
 } // namespace elf
 } // namespace lld
 
 #endif

lld/ELF/Thunks.cpp

void MicroMipsR6Thunk::addSymbols(ThunkSection &isec) {
   d->stOther |= STO_MIPS_MICROMIPS;
 }
 
 InputSection *MicroMipsR6Thunk::getTargetInputSection() const {
   auto &dr = cast<Defined>(destination);
   return dyn_cast<InputSection>(dr.section);
 }
 
-void PPC32PltCallStub::writeTo(uint8_t *buf) {
+void writePPC32PltCallStub(uint8_t *buf, uint64_t gotPltVA,
+                           const InputFile *file, int64_t addend) {
   if (!config->isPic) {
-    uint64_t va = destination.getGotPltVA();
-    write32(buf + 0, 0x3d600000 | (va + 0x8000) >> 16); // lis r11,ha
-    write32(buf + 4, 0x816b0000 | (uint16_t)va);        // lwz r11,l(r11)
-    write32(buf + 8, 0x7d6903a6);                       // mtctr r11
-    write32(buf + 12, 0x4e800420);                      // bctr
+    write32(buf + 0, 0x3d600000 | (gotPltVA + 0x8000) >> 16); // lis r11,ha
+    write32(buf + 4, 0x816b0000 | (uint16_t)gotPltVA);        // lwz r11,l(r11)
+    write32(buf + 8, 0x7d6903a6);                             // mtctr r11
+    write32(buf + 12, 0x4e800420);                            // bctr
     return;
   }
   uint32_t offset;
   if (addend >= 0x8000) {
     // The stub loads an address relative to r30 (.got2+Addend). Addend is
     // almost always 0x8000. The address of .got2 is different in another object
     // file, so a stub cannot be shared.
-    offset = destination.getGotPltVA() - (in.ppc32Got2->getParent()->getVA() +
-                                          file->ppc32Got2OutSecOff + addend);
+    offset = gotPltVA - (in.ppc32Got2->getParent()->getVA() +
   } else {
     // The stub loads an address relative to _GLOBAL_OFFSET_TABLE_ (which is
     // currently the address of .got).
-    offset = destination.getGotPltVA() - in.got->getVA();
+    offset = gotPltVA - in.got->getVA();
   }
   uint16_t ha = (offset + 0x8000) >> 16, l = (uint16_t)offset;
   if (ha == 0) {
     write32(buf + 0, 0x817e0000 | l); // lwz r11,l(r30)
     write32(buf + 4, 0x7d6903a6);     // mtctr r11
     write32(buf + 8, 0x4e800420);     // bctr
     write32(buf + 12, 0x60000000);    // nop
   } else {
     write32(buf + 0, 0x3d7e0000 | ha); // addis r11,r30,ha
     write32(buf + 4, 0x816b0000 | l);  // lwz r11,l(r11)
     write32(buf + 8, 0x7d6903a6);      // mtctr r11
     write32(buf + 12, 0x4e800420);     // bctr
   }
 }
 
+void PPC32PltCallStub::writeTo(uint8_t *buf) {
+  writePPC32PltCallStub(buf, destination.getGotPltVA(), file, addend);
+}
+
 void PPC32PltCallStub::addSymbols(ThunkSection &isec) {
   std::string buf;
   raw_string_ostream os(buf);
   os << format_hex_no_prefix(addend, 8);
   if (!config->isPic)
     os << ".plt_call32.";
   else if (addend >= 0x8000)
     os << ".got2.plt_pic32.";

lld/test/ELF/ppc32-ifunc-nonpreemptible-nopic.s

-# REQUIRES: ppc, asserts
-# XFAIL: *
+# REQUIRES: ppc
 # RUN: llvm-mc -filetype=obj -triple=powerpc %s -o %t.o
 # RUN: ld.lld %t.o -o %t
 # RUN: llvm-readobj -r %t | FileCheck --check-prefix=RELOC %s
 # RUN: llvm-readelf -s %t | FileCheck --check-prefix=SYM %s
-# RUN: llvm-readelf -x .got2 %t | FileCheck --check-prefix=HEX %s
 # RUN: llvm-objdump -d --no-show-raw-insn %t | FileCheck %s
 
 # RELOC:      .rela.dyn {
-# RELOC-NEXT:   0x10020108 R_PPC_IRELATIVE - 0x100100E0
+# RELOC-NEXT:   0x10020110 R_PPC_IRELATIVE - 0x100100E0
 # RELOC-NEXT: }
 
 # SYM: 10010100 0 FUNC GLOBAL DEFAULT {{.*}} func
-# HEX: 0x10020104 10010100
+# HEX: 0x10020110 10010100
 
-.section .got2,"aw"
-.long func
-
-# CHECK:      func_resolver:
+# CHECK:      Disassembly of section .text:
+# CHECK:      .text:
 # CHECK-NEXT: 100100e0: blr
 # CHECK:      _start:
 # CHECK-NEXT:   bl .+12
 # CHECK-NEXT:   lis 9, 4097
 # CHECK-NEXT:   addi 9, 9, 256
 # CHECK-EMPTY:
 # CHECK-NEXT: 00000000.plt_call32.func:
-## 0x10020108 = 65536*4098+264
+## 0x10020110 = 65536*4098+272
 # CHECK-NEXT:   lis 11, 4098
-# CHECK-NEXT:   lwz 11, 264(11)
+# CHECK-NEXT:   lwz 11, 272(11)
 
 .text
 .globl func
 .type func, @gnu_indirect_function
 func:
-.globl func_resolver
-.type func_resolver, @function
-func_resolver:
   blr
 
 .globl _start
 _start:
   bl func
 
   lis 9, func@ha
   la 9, func@l(9)

lld/test/ELF/ppc32-ifunc-nonpreemptible-pic.s

-# REQUIRES: ppc, asserts
-# XFAIL: *
+# REQUIRES: ppc
 # RUN: llvm-mc -filetype=obj -triple=powerpc %s -o %t.o
-# RUN: ld.lld %t.o -o %t
+# RUN: ld.lld -pie %t.o -o %t
 # RUN: llvm-readobj -r %t | FileCheck --check-prefix=RELOC %s
 # RUN: llvm-readelf -s %t | FileCheck --check-prefix=SYM %s
 # RUN: llvm-readelf -x .got2 %t | FileCheck --check-prefix=HEX %s
 # RUN: llvm-objdump -d --no-show-raw-insn %t | FileCheck %s
 
 # RELOC:      .rela.dyn {
-# RELOC-NEXT:   0x10020108 R_PPC_IRELATIVE - 0x100100E0
+# RELOC-NEXT:   0x30240 R_PPC_RELATIVE - 0x101A8
+# RELOC-NEXT:   0x30244 R_PPC_IRELATIVE - 0x10188
 # RELOC-NEXT: }
 
-# SYM: 10010100 0 FUNC GLOBAL DEFAULT {{.*}} func
-# HEX: 0x10020104 10010100
+# SYM: 000101a8 0 FUNC GLOBAL DEFAULT {{.*}} func
+# HEX: 0x00030240 00000000
 
 .section .got2,"aw"
 .long func
 
-# CHECK:      func_resolver:
-# CHECK-NEXT: 100100e0: blr
+# CHECK:      Disassembly of section .text:
+# CHECK:      .text:
+# CHECK-NEXT: 10188: blr
 # CHECK:      _start:
 # CHECK-NEXT:   bl .+12
-# CHECK-NEXT:   lis 9, 4097
-# CHECK-NEXT:   addi 9, 9, 256
+# CHECK-NEXT:   lis 9, 1
+# CHECK-NEXT:   addi 9, 9, 424
 # CHECK-EMPTY:
-# CHECK-NEXT: 00000000.plt_call32.func:
-## 0x10020108 = 65536*4098+264
-# CHECK-NEXT:   lis 11, 4098
-# CHECK-NEXT:   lwz 11, 264(11)
+# CHECK-NEXT: 00008000.got2.plt_pic32.func:
+## 0x10020114 = 65536*4098+276
+# CHECK-NEXT:   lwz 11, -32764(30)
+# CHECK-NEXT:   mtctr 11
+# CHECK-NEXT:   bctr
+# CHECK-NEXT:   nop
 
 .text
 .globl func
 .type func, @gnu_indirect_function
 func:
-.globl func_resolver
-.type func_resolver, @function
-func_resolver:
   blr
 
 .globl _start
 _start:
-  bl func
+  bl func+0x8000@plt
 
   lis 9, func@ha
   la 9, func@l(9)