[lld] Add target support for SystemZ (s390x) (#75643)

This patch adds full support for linking SystemZ (ELF s390x) object
files. Support should be generally complete:
- All relocation types are supported.
- Full shared library support (DYNAMIC, GOT, PLT, ifunc).
- Relaxation of TLS and GOT relocations where appropriate.
- Platform-specific test cases.

In addition to new platform code and the obvious changes, there were a
few additional changes to common code:

- Add three new RelExpr members (R_GOTPLT_OFF, R_GOTPLT_PC, and
R_PLT_GOTREL) needed to support certain s390x relocations. I chose not
to use a platform-specific name since nothing in the definition of these
relocs is actually platform-specific; it is well possible that other
platforms will need the same.

- A couple of tweaks to TLS relocation handling, as the particular
semantics of the s390x versions differ slightly. See comments in the
code.

This was tested by building and testing >1500 Fedora packages, with only
a handful of failures; as these also have issues when building with LLD
on other architectures, they seem unrelated.

Co-authored-by: Tulio Magno Quites Machado Filho <[email protected]>

Author: uweigand

lld/ELF/Arch/SystemZ.cpp

@@ -33,6 +33,7 @@ add_lld_library(lldELF
   Arch/PPC64.cpp
   Arch/RISCV.cpp
   Arch/SPARCV9.cpp
+  Arch/SystemZ.cpp
   Arch/X86.cpp
   Arch/X86_64.cpp
   ARMErrataFix.cpp

lld/ELF/CMakeLists.txt

@@ -200,6 +200,7 @@ static std::tuple<ELFKind, uint16_t, uint8_t> parseEmulation(StringRef emul) {
           .Case("msp430elf", {ELF32LEKind, EM_MSP430})
           .Case("elf64_amdgpu", {ELF64LEKind, EM_AMDGPU})
           .Case("elf64loongarch", {ELF64LEKind, EM_LOONGARCH})
+          .Case("elf64_s390", {ELF64BEKind, EM_S390})
           .Default({ELFNoneKind, EM_NONE});
 
   if (ret.first == ELFNoneKind)
@@ -1137,7 +1138,7 @@ static SmallVector<StringRef, 0> getSymbolOrderingFile(MemoryBufferRef mb) {
 static bool getIsRela(opt::InputArgList &args) {
   // The psABI specifies the default relocation entry format.
   bool rela = is_contained({EM_AARCH64, EM_AMDGPU, EM_HEXAGON, EM_LOONGARCH,
-                            EM_PPC, EM_PPC64, EM_RISCV, EM_X86_64},
+                            EM_PPC, EM_PPC64, EM_RISCV, EM_S390, EM_X86_64},
                            config->emachine);
   // If -z rel or -z rela is specified, use the last option.
   for (auto *arg : args.filtered(OPT_z)) {

lld/ELF/Driver.cpp

@@ -1614,6 +1614,8 @@ static uint16_t getBitcodeMachineKind(StringRef path, const Triple &t) {
     return EM_RISCV;
   case Triple::sparcv9:
     return EM_SPARCV9;
+  case Triple::systemz:
+    return EM_S390;
   case Triple::x86:
     return t.isOSIAMCU() ? EM_IAMCU : EM_386;
   case Triple::x86_64:

lld/ELF/InputFiles.cpp

@@ -655,6 +655,7 @@ static int64_t getTlsTpOffset(const Symbol &s) {
 
     // Variant 2.
   case EM_HEXAGON:
+  case EM_S390:
   case EM_SPARCV9:
   case EM_386:
   case EM_X86_64:
@@ -717,6 +718,10 @@ uint64_t InputSectionBase::getRelocTargetVA(const InputFile *file, RelType type,
   case R_GOT_PC:
   case R_RELAX_TLS_GD_TO_IE:
     return sym.getGotVA() + a - p;
+  case R_GOTPLT_GOTREL:
+    return sym.getGotPltVA() + a - in.got->getVA();
+  case R_GOTPLT_PC:
+    return sym.getGotPltVA() + a - p;
   case R_LOONGARCH_GOT_PAGE_PC:
     if (sym.hasFlag(NEEDS_TLSGD))
       return getLoongArchPageDelta(in.got->getGlobalDynAddr(sym) + a, p, type);
@@ -808,6 +813,8 @@ uint64_t InputSectionBase::getRelocTargetVA(const InputFile *file, RelType type,
     return getLoongArchPageDelta(sym.getPltVA() + a, p, type);
   case R_PLT_GOTPLT:
     return sym.getPltVA() + a - in.gotPlt->getVA();
+  case R_PLT_GOTREL:
+    return sym.getPltVA() + a - in.got->getVA();
   case R_PPC32_PLTREL:
     // R_PPC_PLTREL24 uses the addend (usually 0 or 0x8000) to indicate r30
     // stores _GLOBAL_OFFSET_TABLE_ or .got2+0x8000. The addend is ignored for

lld/ELF/InputSection.cpp

@@ -203,8 +203,9 @@ static bool isAbsoluteValue(const Symbol &sym) {
 
 // Returns true if Expr refers a PLT entry.
 static bool needsPlt(RelExpr expr) {
-  return oneof<R_PLT, R_PLT_PC, R_PLT_GOTPLT, R_LOONGARCH_PLT_PAGE_PC,
-               R_PPC32_PLTREL, R_PPC64_CALL_PLT>(expr);
+  return oneof<R_PLT, R_PLT_PC, R_PLT_GOTREL, R_PLT_GOTPLT, R_GOTPLT_GOTREL,
+               R_GOTPLT_PC, R_LOONGARCH_PLT_PAGE_PC, R_PPC32_PLTREL,
+               R_PPC64_CALL_PLT>(expr);
 }
 
 bool lld::elf::needsGot(RelExpr expr) {
@@ -233,6 +234,8 @@ static RelExpr toPlt(RelExpr expr) {
     return R_PLT_PC;
   case R_ABS:
     return R_PLT;
+  case R_GOTREL:
+    return R_PLT_GOTREL;
   default:
     return expr;
   }
@@ -253,6 +256,8 @@ static RelExpr fromPlt(RelExpr expr) {
     return R_ABS;
   case R_PLT_GOTPLT:
     return R_GOTPLTREL;
+  case R_PLT_GOTREL:
+    return R_GOTREL;
   default:
     return expr;
   }
@@ -979,10 +984,10 @@ bool RelocationScanner::isStaticLinkTimeConstant(RelExpr e, RelType type,
   if (oneof<R_GOTPLT, R_GOT_OFF, R_RELAX_HINT, R_MIPS_GOT_LOCAL_PAGE,
             R_MIPS_GOTREL, R_MIPS_GOT_OFF, R_MIPS_GOT_OFF32, R_MIPS_GOT_GP_PC,
             R_AARCH64_GOT_PAGE_PC, R_GOT_PC, R_GOTONLY_PC, R_GOTPLTONLY_PC,
-            R_PLT_PC, R_PLT_GOTPLT, R_PPC32_PLTREL, R_PPC64_CALL_PLT,
-            R_PPC64_RELAX_TOC, R_RISCV_ADD, R_AARCH64_GOT_PAGE,
-            R_LOONGARCH_PLT_PAGE_PC, R_LOONGARCH_GOT, R_LOONGARCH_GOT_PAGE_PC>(
-          e))
+            R_PLT_PC, R_PLT_GOTREL, R_PLT_GOTPLT, R_GOTPLT_GOTREL, R_GOTPLT_PC,
+            R_PPC32_PLTREL, R_PPC64_CALL_PLT, R_PPC64_RELAX_TOC, R_RISCV_ADD,
+            R_AARCH64_GOT_PAGE, R_LOONGARCH_PLT_PAGE_PC, R_LOONGARCH_GOT,
+            R_LOONGARCH_GOT_PAGE_PC>(e))
     return true;
 
   // These never do, except if the entire file is position dependent or if
@@ -1374,8 +1379,8 @@ static unsigned handleTlsRelocation(RelType type, Symbol &sym,
             R_LOONGARCH_GOT_PAGE_PC, R_GOT_OFF, R_TLSIE_HINT>(expr)) {
     ctx.hasTlsIe.store(true, std::memory_order_relaxed);
     // Initial-Exec relocs can be optimized to Local-Exec if the symbol is
-    // locally defined.
-    if (execOptimize && isLocalInExecutable) {
+    // locally defined.  This is not supported on SystemZ.
+    if (execOptimize && isLocalInExecutable && config->emachine != EM_S390) {
       c.addReloc({R_RELAX_TLS_IE_TO_LE, type, offset, addend, &sym});
     } else if (expr != R_TLSIE_HINT) {
       sym.setFlags(NEEDS_TLSIE);
@@ -1534,8 +1539,10 @@ void RelocationScanner::scan(ArrayRef<RelTy> rels) {
   // For EhInputSection, OffsetGetter expects the relocations to be sorted by
   // r_offset. In rare cases (.eh_frame pieces are reordered by a linker
   // script), the relocations may be unordered.
+  // On SystemZ, all sections need to be sorted by r_offset, to allow TLS
+  // relaxation to be handled correctly - see SystemZ::getTlsGdRelaxSkip.
   SmallVector<RelTy, 0> storage;
-  if (isa<EhInputSection>(sec))
+  if (isa<EhInputSection>(sec) || config->emachine == EM_S390)
     rels = sortRels(rels, storage);
 
   end = static_cast<const void *>(rels.end());

lld/ELF/Relocations.cpp

@@ -40,11 +40,14 @@ enum RelExpr {
   R_GOTPLT,
   R_GOTPLTREL,
   R_GOTREL,
+  R_GOTPLT_GOTREL,
+  R_GOTPLT_PC,
   R_NONE,
   R_PC,
   R_PLT,
   R_PLT_PC,
   R_PLT_GOTPLT,
+  R_PLT_GOTREL,
   R_RELAX_HINT,
   R_RELAX_GOT_PC,
   R_RELAX_GOT_PC_NOPIC,

lld/ELF/Relocations.h

@@ -445,6 +445,7 @@ static std::pair<ELFKind, uint16_t> parseBfdName(StringRef s) {
       .Case("elf32-msp430", {ELF32LEKind, EM_MSP430})
       .Case("elf32-loongarch", {ELF32LEKind, EM_LOONGARCH})
       .Case("elf64-loongarch", {ELF64LEKind, EM_LOONGARCH})
+      .Case("elf64-s390", {ELF64BEKind, EM_S390})
       .Default({ELFNoneKind, EM_NONE});
 }
 

lld/ELF/ScriptParser.cpp

@@ -1419,6 +1419,9 @@ DynamicSection<ELFT>::computeContents() {
     case EM_MIPS:
       addInSec(DT_MIPS_PLTGOT, *in.gotPlt);
       break;
+    case EM_S390:
+      addInSec(DT_PLTGOT, *in.got);
+      break;
     case EM_SPARCV9:
       addInSec(DT_PLTGOT, *in.plt);
       break;

lld/ELF/SyntheticSections.cpp

@@ -87,6 +87,8 @@ TargetInfo *elf::getTarget() {
     return getRISCVTargetInfo();
   case EM_SPARCV9:
     return getSPARCV9TargetInfo();
+  case EM_S390:
+    return getSystemZTargetInfo();
   case EM_X86_64:
     return getX86_64TargetInfo();
   default: