[lld][LoongArch] Implement TLSDESC GD/LD to IE/LE.

ylzsx · ylzsx · commit 30939363f35f · 2024-12-26T08:56:55.000+08:00
Support TLSDESC to initial-exec or local-exec optimizations.
Introduce a new hook RE_LOONGARCH_RELAX_TLS_GD_TO_IE_PAGE_PC and use
existing R_RELAX_TLS_GD_TO_IE_ABS to support TLSDESC =&gt; IE, while use
existing R_RELAX_TLS_GD_TO_LE to support TLSDESC =&gt; LE.

Different code models correspond to different TLSDESC code sequences.
In normal or medium code model, there are two forms of code sequences:
```
pcalau12i  $a0, %desc_pc_hi20(sym_desc)
addi.d     $a0, $a0, %desc_pc_lo12(sym_desc)
ld.d       $ra, $a0, %desc_ld(sym_desc)
jirl       $ra, $ra, %desc_call(sym_desc)
---
pcaddi     $a0, %desc_pcrel_20(sym_desc)
ld.d       $ra, $a0, %desc_ld(sym_desc)
jirl       $ra, $ra, %desc_call(sym_desc)
```

In extreme code model, there is only one:
```
pcalau12i  $a0, %desc_pc_hi20(sym_desc_large)
addi.d     $a1, $zero, %desc_pc_lo12(sym_desc_large)
lu32i.d    $a1, %desc64_pc_lo20(sym_desc_large)
lu52i.d    $a1, $a1, %desc64_pc_hi12(sym_desc_large)
add.d      $a0, $a0, $a1
ld.d       $ra, $a0, %desc_ld(sym_desc_large)
jirl       $ra, $ra, %desc_call(sym_desc_large)
```

Simplicity, we tend to convert the preceding instructions to NOP in
normal or medium code model, due to both forms of code sequence
(corresponding to relocation combinations:
`R_LARCH_TLS_DESC_PC_HI20+R_LARCH_TLS_DESC_PC_LO12` and `R_LARCH_TLS_DESC_PCREL20_S2`)
have same process.

However, for the extreme code model, IE optimization requires a
temporary register $a1, which exists in the original preceding code
sequence. To avoid additional bookkeeping, in the exterme code model, we
convert the last two instructions to NOP. Fortunately, the extreme code
model only has one form (donot use `R_LARCH_TLS_DESC_PCREL20_S2` relocation),
and it makes this conversion strategy feasible.
diff --git a/lld/ELF/Arch/LoongArch.cpp b/lld/ELF/Arch/LoongArch.cpp
@@ -39,7 +39,15 @@ class LoongArch final : public TargetInfo {
   void relocate(uint8_t *loc, const Relocation &rel,
                 uint64_t val) const override;
   bool relaxOnce(int pass) const override;
+  RelExpr adjustTlsExpr(RelType type, RelExpr expr) const override;
+  void relocateAlloc(InputSectionBase &sec, uint8_t *buf) const override;
   void finalizeRelax(int passes) const override;
+
+private:
+  void tlsdescToIe(uint8_t *loc, const Relocation &rel, uint64_t val,
+                   bool isExtreme) const;
+  void tlsdescToLe(uint8_t *loc, const Relocation &rel, uint64_t val,
+                   bool isExtreme) const;
 };
 } // end anonymous namespace
 
@@ -53,16 +61,23 @@ enum Op {
   ADDI_W = 0x02800000,
   ADDI_D = 0x02c00000,
   ANDI = 0x03400000,
+  ORI = 0x03800000,
+  LU12I_W = 0x14000000,
+  LU32I_D = 0x16000000,
+  LU52I_D = 0x03000000,
+  PCALAU12I = 0x1a000000,
   PCADDU12I = 0x1c000000,
   LD_W = 0x28800000,
   LD_D = 0x28c00000,
+  LDX_D = 0x380c0000,
   JIRL = 0x4c000000,
 };
 
 enum Reg {
   R_ZERO = 0,
   R_RA = 1,
   R_TP = 2,
+  R_A0 = 4,
   R_T0 = 12,
   R_T1 = 13,
   R_T2 = 14,
@@ -131,6 +146,10 @@ static uint32_t extractBits(uint64_t v, uint32_t begin, uint32_t end) {
   return begin == 63 ? v >> end : (v & ((1ULL << (begin + 1)) - 1)) >> end;
 }
 
+static uint32_t getD5(uint64_t v) { return extractBits(v, 4, 0); }
+
+static uint32_t getJ5(uint64_t v) { return extractBits(v, 9, 5); }
+
 static uint32_t setD5k16(uint32_t insn, uint32_t imm) {
   uint32_t immLo = extractBits(imm, 15, 0);
   uint32_t immHi = extractBits(imm, 20, 16);
@@ -812,6 +831,255 @@ static bool relax(Ctx &ctx, InputSection &sec) {
   return changed;
 }
 
+// Convert TLSDESC GD/LD to IE.
+// The code sequence obtained in the normal or medium code model is as follows:
+//  * pcalau12i $a0, %ie_pc_hi20(sym_ie)
+//  * ld.[wd]   $a0, $a0, %ie_pc_lo12(sym_ie)
+//
+// The code sequence obtained in the extreme code model is as follows:
+//  * pcalau12i $a0, %ie_pc_hi20(sym_ie_large)
+//  * addi.d    $a1, $r0, %ie_pc_lo12(sym_ie_large)
+//  * lu32i.d   $a1, %ie64_pc_lo20(sym_ie_large)
+//  * lu52i.d   $a1, $a1, %ie64_pc_hi12(sym_ie_large)
+//  * ldx.d     $a0, $a0, $a1
+//
+//  The optimization for tlsdescToIe and tlsdescToLe in the extreme code model
+//  always preserves the preceding code sequence and converts the last
+//  instructions to NOP, while the optimization for the normal or medium code
+//  models of tlsdescToIe and tlsdescToLe do the oppsite. This is because, in
+//  the extreme code model, tlsdescToIe requires a temporary register $a1, and
+//  the preceding unoptimized tls.desc code sequence contains this temporary
+//  register, eliminating additional bookkeeping.
+void LoongArch::tlsdescToIe(uint8_t *loc, const Relocation &rel, uint64_t val,
+                            bool isExtreme) const {
+  if (isExtreme) { // extreme
+    const uint32_t currInsn = read32le(loc);
+    switch (rel.type) {
+    case R_LARCH_TLS_DESC_PC_HI20:
+      write32le(loc, insn(PCALAU12I, R_A0, 0, 0)); // pcalau12i $a0, %ie_pc_hi20
+      relocateNoSym(loc, R_LARCH_TLS_IE_PC_HI20, val);
+      break;
+    case R_LARCH_TLS_DESC_PC_LO12:
+      write32le(loc, insn(ADDI_D, getD5(currInsn), R_ZERO,
+                          0)); // addi.d $a1, $r0, %ie_pc_lo12
+      relocateNoSym(loc, R_LARCH_TLS_IE_PC_LO12, val);
+      break;
+    case R_LARCH_TLS_DESC64_PC_LO20:
+      write32le(loc, insn(LU32I_D, getD5(currInsn), 0,
+                          0)); // lu32i.d $a1, %ie64_pc_lo20
+      relocateNoSym(loc, R_LARCH_TLS_IE64_PC_LO20, val);
+      break;
+    case R_LARCH_TLS_DESC64_PC_HI12:
+      write32le(loc, insn(LU52I_D, getD5(currInsn), getJ5(currInsn),
+                          0)); // lu52i.d $a1, $a1, %ie64_pc_hi12
+      relocateNoSym(loc, R_LARCH_TLS_IE64_PC_HI12, val);
+      write32le(loc + 4, insn(LDX_D, R_A0, R_A0,
+                              getD5(currInsn))); // ldx.d $a0, $a0, $a1
+      break;
+    case R_LARCH_TLS_DESC_LD:
+    case R_LARCH_TLS_DESC_CALL:
+      write32le(loc, insn(ANDI, R_ZERO, R_ZERO, 0)); // nop
+      break;
+    default:
+      llvm_unreachable("unsupported relocation for TLSDESC to IE");
+    }
+  } else { // normal or medium
+    switch (rel.type) {
+    case R_LARCH_TLS_DESC_PC_HI20:
+    case R_LARCH_TLS_DESC_PC_LO12:
+    case R_LARCH_TLS_DESC_PCREL20_S2:
+      write32le(loc, insn(ANDI, R_ZERO, R_ZERO, 0)); // nop
+      break;
+    case R_LARCH_TLS_DESC_LD:
+      write32le(loc, insn(PCALAU12I, R_A0, 0, 0)); // pcalau12i $a0, %ie_pc_hi20
+      relocateNoSym(loc, R_LARCH_TLS_IE_PC_HI20, val);
+      break;
+    case R_LARCH_TLS_DESC_CALL:
+      write32le(loc, insn(ctx.arg.is64 ? LD_D : LD_W, R_A0, R_A0,
+                          0)); // ld.[wd] $a0, $a0, %ie_pc_lo12
+      relocateNoSym(loc, R_LARCH_TLS_IE_PC_LO12, val);
+      break;
+    default:
+      llvm_unreachable("unsupported relocation for TLSDESC to IE");
+    }
+  }
+}
+
+// Convert TLSDESC GD/LD to LE.
+// The code sequence obtained in the normal or medium code model is as follows:
+//  * lu12i.w $a0, %le_hi20(sym_le)  # le_hi20 != 0
+//  * ori $a0 $a0, %le_lo12(sym_le)
+//
+// The code sequence obtained in extreme code model is as follows:
+//  * lu12i.w $a0, %le_hi20(sym_le_large)
+//  * ori     $a0, $a0, %le_lo12(sym_le_large)
+//  * lu32i.d $a0, %le64_lo20(sym_le_large)
+//  * lu52i.d $a0, $a0, %le64_hi20(sym_le_large)
+//
+// Note: In the extreme code model, it is possible for the generated code
+// sequence to include NOPs at both beginning and the end. Likely,
+//  * nop; ori $a0, $r0, %le_lo12; nop; nop
+// This occurs because the four instructions are used to assemble each part of a
+// 64-bit value independently, without affecting each other. Therefore, to
+// obtain an efficient code sequence, NOPs are used as much as possible.
+// Additionally, the extreme code model does not participate in relaxation
+// optimization.
+void LoongArch::tlsdescToLe(uint8_t *loc, const Relocation &rel, uint64_t val,
+                            bool isExtreme) const {
+  if (isExtreme) { // extreme
+    switch (rel.type) {
+    case R_LARCH_TLS_DESC_PC_HI20:
+      if (uint32_t hi20 = extractBits(val, 31, 12))
+        write32le(loc,
+                  insn(LU12I_W, R_A0, hi20, 0)); // lu12i.w $a0, $a0, %le_hi20
+      else
+        write32le(loc, insn(ANDI, R_ZERO, R_ZERO, 0)); // nop
+      break;
+    case R_LARCH_TLS_DESC_PC_LO12:
+      if (extractBits(val, 31, 12))
+        write32le(loc,
+                  insn(ORI, R_A0, R_A0, lo12(val))); // ori $a0, $a0, %le_lo12
+      else
+        write32le(loc,
+                  insn(ORI, R_A0, R_ZERO, lo12(val))); // ori $a0, $r0, %le_lo12
+      break;
+    case R_LARCH_TLS_DESC64_PC_LO20:
+      // If val[31] is 1, lu12i.w will set $a0[51-32]. So, clear it.
+      if (uint32_t lo20 = extractBits(val, 51, 32) || extractBits(val, 31, 31))
+        write32le(loc, insn(LU32I_D, R_A0, lo20, 0)); // lu32i.d $a0, %le64_lo20
+      else
+        write32le(loc, insn(ANDI, R_ZERO, R_ZERO, 0)); // nop
+      break;
+    case R_LARCH_TLS_DESC64_PC_HI12:
+      // If val[31] is 1, lu12i.w will set $a0[63-52]. So, clear it.
+      if (uint32_t hi12 =
+              extractBits(val, 63, 52) || extractBits(val, 31, 31)) {
+        write32le(loc, insn(LU52I_D, R_A0, R_A0,
+                            hi12)); // lu52i.d $a0, $a0, %le64_hi20
+        // Due to add.d does not include relocation, an additional NOP needs to
+        // be generated.
+        write32le(loc + 4, insn(ANDI, R_ZERO, R_ZERO, 0)); // nop
+      } else {
+        write32le(loc, insn(ANDI, R_ZERO, R_ZERO, 0));     // nop
+        write32le(loc + 4, insn(ANDI, R_ZERO, R_ZERO, 0)); // nop
+      }
+      break;
+    case R_LARCH_TLS_DESC_LD:
+    case R_LARCH_TLS_DESC_CALL:
+      write32le(loc, insn(ANDI, R_ZERO, R_ZERO, 0)); // nop
+      break;
+    default:
+      llvm_unreachable("unsupported relocation for TLSDESC to LE");
+    }
+  } else { // normal or medium
+    switch (rel.type) {
+    case R_LARCH_TLS_DESC_PC_HI20:
+    case R_LARCH_TLS_DESC_PC_LO12:
+    case R_LARCH_TLS_DESC_PCREL20_S2:
+      write32le(loc, insn(ANDI, R_ZERO, R_ZERO, 0)); // nop
+      break;
+    case R_LARCH_TLS_DESC_LD:
+      if (isUInt<12>(val))
+        write32le(loc, insn(ANDI, R_ZERO, R_ZERO, 0)); // nop
+      else if (isInt<32>(val))
+        write32le(loc, insn(LU12I_W, R_A0, extractBits(val, 31, 12),
+                            0)); // lu12i.w $a0, %le_hi20
+      else
+        Err(ctx) << val
+                 << " exceeds the range of medium code model in tlsdescToLe";
+      break;
+    case R_LARCH_TLS_DESC_CALL:
+      if (isUInt<12>(val))
+        write32le(loc, insn(ORI, R_A0, R_ZERO, val)); // ori $a0, $r0, %le_lo12
+      else if (isInt<32>(val))
+        write32le(loc,
+                  insn(ORI, R_A0, R_A0, lo12(val))); // ori $a0, $a0, %le_lo12
+      else
+        Err(ctx) << val
+                 << " exceeds the range of medium code model in tlsdescToLe";
+      break;
+    default:
+      llvm_unreachable("unsupported relocation for TLSDESC to LE");
+    }
+  }
+}
+
+// During GD_TO_IE, the converted code sequence always includes an instruction
+// related to the Lo12 relocation (ld.[wd] or addi.d). To obtain correct val in
+// `getRelocTargetVA`, expr of this instruction should be adjusted to
+// R_RELAX_TLS_GD_TO_IE_ABS, while expr of other valid instructions (not NOP)
+// should be adjusted to RE_LOONGARCH_RELAX_TLS_GD_TO_IE_PAGE_PC.
+// See the comment in tlsdescToIe for detailed information.
+//
+// Specifically, in the normal or medium code model, the instruction with
+// relocation R_LARCH_TLS_DESC_CALL is the candidate of Lo12 relocation. And in
+// the extreme code model, the instruction with R_LARCH_TLS_DESC_PC_LO12 is the
+// candidate. Meanwhile, in the normal or medium code model, the instruction
+// with R_LARCH_TLS_DESC_PC_LO12 will always be converted to NOP. Similarly, in
+// the extreme code model, the instruction with R_LARCH_TLS_DESC_CALL will be
+// converted to NOP. Therefore, the adjustment of the expr here is safe.
+RelExpr LoongArch::adjustTlsExpr(RelType type, RelExpr expr) const {
+  if (expr == R_RELAX_TLS_GD_TO_IE) {
+    if (type != R_LARCH_TLS_DESC_PC_LO12 && type != R_LARCH_TLS_DESC_CALL)
+      return RE_LOONGARCH_RELAX_TLS_GD_TO_IE_PAGE_PC;
+    return R_RELAX_TLS_GD_TO_IE_ABS;
+  }
+  return expr;
+}
+
+void LoongArch::relocateAlloc(InputSectionBase &sec, uint8_t *buf) const {
+  const unsigned bits = ctx.arg.is64 ? 64 : 32;
+  uint64_t secAddr = sec.getOutputSection()->addr;
+  if (auto *s = dyn_cast<InputSection>(&sec))
+    secAddr += s->outSecOff;
+  else if (auto *ehIn = dyn_cast<EhInputSection>(&sec))
+    secAddr += ehIn->getParent()->outSecOff;
+  bool isExtreme = false;
+  const ArrayRef<Relocation> relocs = sec.relocs();
+  for (size_t i = 0, size = relocs.size(); i != size; ++i) {
+    const Relocation &rel = relocs[i];
+    uint8_t *loc = buf + rel.offset;
+    const uint64_t val = SignExtend64(
+        sec.getRelocTargetVA(ctx, rel, secAddr + rel.offset), bits);
+
+    switch (rel.expr) {
+    case R_RELAX_HINT:
+      continue;
+    case RE_LOONGARCH_RELAX_TLS_GD_TO_IE_PAGE_PC:
+      if (rel.type == R_LARCH_TLS_DESC_PC_HI20) {
+        // The relocation sequence in the extreme code model is as follows:
+        //
+        //  * i   -- R_LARCH_TLS_DESC_PC_HI20
+        //  * i+1 -- R_LARCH_TLS_DESC_PC_LO12
+        //  * i+2 -- R_LARCH_TLS_DESC64_PC_LO20
+        //  * i+3 -- R_LARCH_TLS_DESC64_PC_HI12
+        isExtreme =
+            (i + 2 < size && relocs[i + 2].type == R_LARCH_TLS_DESC64_PC_LO20);
+      }
+      [[fallthrough]];
+    case R_RELAX_TLS_GD_TO_IE_ABS:
+      tlsdescToIe(loc, rel, val, isExtreme);
+      continue;
+    case R_RELAX_TLS_GD_TO_LE:
+      if (rel.type == R_LARCH_TLS_DESC_PC_HI20) {
+        // The relocation sequence in the extreme code model is as follows:
+        //
+        //  * i   -- R_LARCH_TLS_DESC_PC_HI20
+        //  * i+1 -- R_LARCH_TLS_DESC_PC_LO12
+        //  * i+2 -- R_LARCH_TLS_DESC64_PC_LO20
+        //  * i+3 -- R_LARCH_TLS_DESC64_PC_HI12
+        isExtreme =
+            (i + 2 < size && relocs[i + 2].type == R_LARCH_TLS_DESC64_PC_LO20);
+      }
+      tlsdescToLe(loc, rel, val, isExtreme);
+      continue;
+    default:
+      break;
+    }
+    relocate(loc, rel, val);
+  }
+}
+
 // When relaxing just R_LARCH_ALIGN, relocDeltas is usually changed only once in
 // the absence of a linker script. For call and load/store R_LARCH_RELAX, code
 // shrinkage may reduce displacement and make more relocations eligible for
diff --git a/lld/ELF/InputSection.cpp b/lld/ELF/InputSection.cpp
@@ -825,6 +825,7 @@ uint64_t InputSectionBase::getRelocTargetVA(Ctx &ctx, const Relocation &r,
   case R_GOTPLT_PC:
     return r.sym->getGotPltVA(ctx) + a - p;
   case RE_LOONGARCH_GOT_PAGE_PC:
+  case RE_LOONGARCH_RELAX_TLS_GD_TO_IE_PAGE_PC:
     if (r.sym->hasFlag(NEEDS_TLSGD))
       return getLoongArchPageDelta(ctx.in.got->getGlobalDynAddr(*r.sym) + a, p,
                                    r.type);
diff --git a/lld/ELF/Relocations.cpp b/lld/ELF/Relocations.cpp
@@ -1316,22 +1316,10 @@ unsigned RelocationScanner::handleTlsRelocation(RelExpr expr, RelType type,
   if (ctx.arg.emachine == EM_MIPS)
     return handleMipsTlsRelocation(ctx, type, sym, *sec, offset, addend, expr);
 
-  // LoongArch does not yet implement transition from TLSDESC to LE/IE, so
-  // generate TLSDESC dynamic relocation for the dynamic linker to handle.
-  if (ctx.arg.emachine == EM_LOONGARCH &&
-      oneof<RE_LOONGARCH_TLSDESC_PAGE_PC, R_TLSDESC, R_TLSDESC_PC,
-            R_TLSDESC_CALL>(expr)) {
-    if (expr != R_TLSDESC_CALL) {
-      sym.setFlags(NEEDS_TLSDESC);
-      sec->addReloc({expr, type, offset, addend, &sym});
-    }
-    return 1;
-  }
-
   bool isRISCV = ctx.arg.emachine == EM_RISCV;
 
   if (oneof<RE_AARCH64_TLSDESC_PAGE, R_TLSDESC, R_TLSDESC_CALL, R_TLSDESC_PC,
-            R_TLSDESC_GOTPLT>(expr) &&
+            R_TLSDESC_GOTPLT, RE_LOONGARCH_TLSDESC_PAGE_PC>(expr) &&
       ctx.arg.shared) {
     // R_RISCV_TLSDESC_{LOAD_LO12,ADD_LO12_I,CALL} reference a label. Do not
     // set NEEDS_TLSDESC on the label.
@@ -1350,7 +1338,10 @@ unsigned RelocationScanner::handleTlsRelocation(RelExpr expr, RelType type,
   // optimization as well.
   bool execOptimize =
       !ctx.arg.shared && ctx.arg.emachine != EM_ARM &&
-      ctx.arg.emachine != EM_HEXAGON && ctx.arg.emachine != EM_LOONGARCH &&
+      ctx.arg.emachine != EM_HEXAGON &&
+      !(ctx.arg.emachine == EM_LOONGARCH &&
+        expr != RE_LOONGARCH_TLSDESC_PAGE_PC && expr != R_TLSDESC &&
+        expr != R_TLSDESC_PC && expr != R_TLSDESC_CALL) &&
       !(isRISCV && expr != R_TLSDESC_PC && expr != R_TLSDESC_CALL) &&
       !sec->file->ppc64DisableTLSRelax;
 
@@ -1401,7 +1392,7 @@ unsigned RelocationScanner::handleTlsRelocation(RelExpr expr, RelType type,
 
   if (oneof<RE_AARCH64_TLSDESC_PAGE, R_TLSDESC, R_TLSDESC_CALL, R_TLSDESC_PC,
             R_TLSDESC_GOTPLT, R_TLSGD_GOT, R_TLSGD_GOTPLT, R_TLSGD_PC,
-            RE_LOONGARCH_TLSGD_PAGE_PC>(expr)) {
+            RE_LOONGARCH_TLSGD_PAGE_PC, RE_LOONGARCH_TLSDESC_PAGE_PC>(expr)) {
     if (!execOptimize) {
       sym.setFlags(NEEDS_TLSGD);
       sec->addReloc({expr, type, offset, addend, &sym});
diff --git a/lld/ELF/Relocations.h b/lld/ELF/Relocations.h
@@ -128,6 +128,7 @@ enum RelExpr {
   RE_LOONGARCH_GOT,
   RE_LOONGARCH_GOT_PAGE_PC,
   RE_LOONGARCH_TLSGD_PAGE_PC,
+  RE_LOONGARCH_RELAX_TLS_GD_TO_IE_PAGE_PC,
   RE_LOONGARCH_TLSDESC_PAGE_PC,
 };
 
