[PPC64] Set the number of relocations processed for R_PPC64_TLS[GL]D to 2

Summary:
R_PPC64_TLSGD and R_PPC64_TLSLD are used as markers on TLS code sequences. After GD-to-IE or GD-to-LE relaxation, the next relocation R_PPC64_REL24 should be skipped to not create a false dependency on __tls_get_addr. When linking statically, the false dependency may cause an "undefined symbol: __tls_get_addr" error.

R_PPC64_GOT_TLSGD16_HA
R_PPC64_GOT_TLSGD16_LO
R_PPC64_TLSGD R_TLSDESC_CALL
R_PPC64_REL24 __tls_get_addr

Reviewers: ruiu, sfertile, syzaara, espindola

Reviewed By: sfertile

Subscribers: emaste, nemanjai, arichardson, kbarton, jsji, llvm-commits, tamur

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D57673

llvm-svn: 353262

lld/ELF/Arch/PPC64.cpp

@@ -111,6 +111,7 @@ namespace {
 class PPC64 final : public TargetInfo {
 public:
   PPC64();
+  int getTlsGdRelaxSkip(RelType Type) const override;
   uint32_t calcEFlags() const override;
   RelExpr getRelExpr(RelType Type, const Symbol &S,
                      const uint8_t *Loc) const override;
@@ -241,6 +242,20 @@ PPC64::PPC64() {
   write32(TrapInstr.data(), 0x7fe00008);
 }
 
+int PPC64::getTlsGdRelaxSkip(RelType Type) const {
+  // A __tls_get_addr call instruction is marked with 2 relocations:
+  //
+  //   R_PPC64_TLSGD / R_PPC64_TLSLD: marker relocation
+  //   R_PPC64_REL24: __tls_get_addr
+  //
+  // After the relaxation we no longer call __tls_get_addr and should skip both
+  // relocations to not create a false dependence on __tls_get_addr being
+  // defined.
+  if (Type == R_PPC64_TLSGD || Type == R_PPC64_TLSLD)
+    return 2;
+  return 1;
+}
+
 static uint32_t getEFlags(InputFile *File) {
   if (Config->EKind == ELF64BEKind)
     return cast<ObjFile<ELF64BE>>(File)->getObj().getHeader()->e_flags;

lld/ELF/Arch/X86.cpp

@@ -23,6 +23,7 @@ namespace {
 class X86 : public TargetInfo {
 public:
   X86();
+  int getTlsGdRelaxSkip(RelType Type) const override;
   RelExpr getRelExpr(RelType Type, const Symbol &S,
                      const uint8_t *Loc) const override;
   int64_t getImplicitAddend(const uint8_t *Buf, RelType Type) const override;
@@ -58,7 +59,6 @@ X86::X86() {
   GotPltEntrySize = 4;
   PltEntrySize = 16;
   PltHeaderSize = 16;
-  TlsGdRelaxSkip = 2;
   TrapInstr = {0xcc, 0xcc, 0xcc, 0xcc}; // 0xcc = INT3
 
   // Align to the non-PAE large page size (known as a superpage or huge page).
@@ -66,6 +66,10 @@ X86::X86() {
   DefaultImageBase = 0x400000;
 }
 
+int X86::getTlsGdRelaxSkip(RelType Type) const {
+  return 2;
+}
+
 RelExpr X86::getRelExpr(RelType Type, const Symbol &S,
                         const uint8_t *Loc) const {
   switch (Type) {

lld/ELF/Arch/X86_64.cpp

@@ -25,6 +25,7 @@ namespace {
 template <class ELFT> class X86_64 : public TargetInfo {
 public:
   X86_64();
+  int getTlsGdRelaxSkip(RelType Type) const override;
   RelExpr getRelExpr(RelType Type, const Symbol &S,
                      const uint8_t *Loc) const override;
   RelType getDynRel(RelType Type) const override;
@@ -65,7 +66,6 @@ template <class ELFT> X86_64<ELFT>::X86_64() {
   GotPltEntrySize = 8;
   PltEntrySize = 16;
   PltHeaderSize = 16;
-  TlsGdRelaxSkip = 2;
   TrapInstr = {0xcc, 0xcc, 0xcc, 0xcc}; // 0xcc = INT3
 
   // Align to the large page size (known as a superpage or huge page).
@@ -73,6 +73,11 @@ template <class ELFT> X86_64<ELFT>::X86_64() {
   DefaultImageBase = 0x200000;
 }
 
+template <class ELFT>
+int X86_64<ELFT>::getTlsGdRelaxSkip(RelType Type) const {
+  return 2;
+}
+
 template <class ELFT>
 RelExpr X86_64<ELFT>::getRelExpr(RelType Type, const Symbol &S,
                                  const uint8_t *Loc) const {

lld/ELF/Relocations.cpp

@@ -205,7 +205,7 @@ handleTlsRelocation(RelType Type, Symbol &Sym, InputSectionBase &C,
       C.Relocations.push_back(
           {Target->adjustRelaxExpr(Type, nullptr, R_RELAX_TLS_LD_TO_LE), Type,
            Offset, Addend, &Sym});
-      return Target->TlsGdRelaxSkip;
+      return Target->getTlsGdRelaxSkip(Type);
     }
     if (Expr == R_TLSLD_HINT)
       return 1;
@@ -278,7 +278,7 @@ handleTlsRelocation(RelType Type, Symbol &Sym, InputSectionBase &C,
           {Target->adjustRelaxExpr(Type, nullptr, R_RELAX_TLS_GD_TO_LE), Type,
            Offset, Addend, &Sym});
     }
-    return Target->TlsGdRelaxSkip;
+    return Target->getTlsGdRelaxSkip(Type);
   }
 
   // Initial-Exec relocs can be relaxed to Local-Exec if the symbol is locally

lld/ELF/Target.h

@@ -32,6 +32,7 @@ public:
   virtual void writeGotPlt(uint8_t *Buf, const Symbol &S) const {};
   virtual void writeIgotPlt(uint8_t *Buf, const Symbol &S) const;
   virtual int64_t getImplicitAddend(const uint8_t *Buf, RelType Type) const;
+  virtual int getTlsGdRelaxSkip(RelType Type) const { return 1; }
 
   // If lazy binding is supported, the first entry of the PLT has code
   // to call the dynamic linker to resolve PLT entries the first time
@@ -80,7 +81,6 @@ public:
 
   virtual ~TargetInfo();
 
-  unsigned TlsGdRelaxSkip = 1;
   unsigned PageSize = 4096;
   unsigned DefaultMaxPageSize = 4096;
 

lld/test/ELF/ppc64-gd-to-ie.s

@@ -69,10 +69,6 @@ other_reg:
         mtlr 0
         blr
 
-        .globl __tls_get_addr
-        .type __tls_get_addr,@function
-__tls_get_addr:
-
 
 # CheckGot: .got          00000018 00000000100200c0 DATA
 # .got is at 0x100200c0 so the toc-base is 100280c0.

lld/test/ELF/ppc64-tls-gd-le.s

@@ -50,10 +50,6 @@ _start:                                   # @_start
 .Lfunc_end0:
 	.size	_start, .Lfunc_end0-.Lfunc_begin0
 
-.globl __tls_get_addr
-.type __tls_get_addr,@function
-__tls_get_addr:
-
                                         # -- End function
 	.type	a,@object               # @a
 	.section	.tdata,"awT",@progbits