[RISCV] Use OS-specific stack-guard ABI for Fuchsia

Fuchsia provides a slot relative to tp for the stack-guard value,
which is cheaper to materialize than the default GOT load.

Reviewed By: phosek

Differential Revision: https://reviews.llvm.org/D143353

Author: frobtech

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -14221,6 +14221,25 @@ bool RISCVTargetLowering::preferScalarizeSplat(unsigned Opc) const {
   return true;
 }
 
+static Value *useTpOffset(IRBuilderBase &IRB, unsigned Offset) {
+  Module *M = IRB.GetInsertBlock()->getParent()->getParent();
+  Function *ThreadPointerFunc =
+      Intrinsic::getDeclaration(M, Intrinsic::thread_pointer);
+  return IRB.CreatePointerCast(
+      IRB.CreateConstGEP1_32(IRB.getInt8Ty(),
+                             IRB.CreateCall(ThreadPointerFunc), Offset),
+      IRB.getInt8PtrTy()->getPointerTo(0));
+}
+
+Value *RISCVTargetLowering::getIRStackGuard(IRBuilderBase &IRB) const {
+  // Fuchsia provides a fixed TLS slot for the stack cookie.
+  // <zircon/tls.h> defines ZX_TLS_STACK_GUARD_OFFSET with this value.
+  if (Subtarget.isTargetFuchsia())
+    return useTpOffset(IRB, -0x10);
+
+  return TargetLowering::getIRStackGuard(IRB);
+}
+
 #define GET_REGISTER_MATCHER
 #include "RISCVGenAsmMatcher.inc"
 

llvm/lib/Target/RISCV/RISCVISelLowering.h

@@ -633,6 +633,10 @@ class RISCVTargetLowering : public TargetLowering {
     return Scale == 1;
   }
 
+  /// If the target has a standard location for the stack protector cookie,
+  /// returns the address of that location. Otherwise, returns nullptr.
+  Value *getIRStackGuard(IRBuilderBase &IRB) const override;
+
 private:
   /// RISCVCCAssignFn - This target-specific function extends the default
   /// CCValAssign with additional information used to lower RISC-V calling

llvm/lib/Target/RISCV/RISCVSubtarget.h

@@ -176,6 +176,8 @@ class RISCVSubtarget : public RISCVGenSubtargetInfo {
   const LegalizerInfo *getLegalizerInfo() const override;
   const RegisterBankInfo *getRegBankInfo() const override;
 
+  bool isTargetFuchsia() const { return getTargetTriple().isOSFuchsia(); }
+
   bool useConstantPoolForLargeInts() const;
 
   // Maximum cost used for building integers, integers will be put into constant

llvm/test/CodeGen/RISCV/stack-protector-target.ll

@@ -0,0 +1,32 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+
+;; Test target-specific stack cookie location.
+;
+; RUN: llc -mtriple=riscv64-fuchsia < %s | FileCheck --check-prefix=FUCHSIA-RISCV64 %s
+
+define void @func() sspreq {
+; FUCHSIA-RISCV64-LABEL: func:
+; FUCHSIA-RISCV64:       # %bb.0:
+; FUCHSIA-RISCV64-NEXT:    addi sp, sp, -32
+; FUCHSIA-RISCV64-NEXT:    .cfi_def_cfa_offset 32
+; FUCHSIA-RISCV64-NEXT:    sd ra, 24(sp) # 8-byte Folded Spill
+; FUCHSIA-RISCV64-NEXT:    .cfi_offset ra, -8
+; FUCHSIA-RISCV64-NEXT:    ld a0, -16(tp)
+; FUCHSIA-RISCV64-NEXT:    sd a0, 16(sp)
+; FUCHSIA-RISCV64-NEXT:    addi a0, sp, 12
+; FUCHSIA-RISCV64-NEXT:    call capture@plt
+; FUCHSIA-RISCV64-NEXT:    ld a0, -16(tp)
+; FUCHSIA-RISCV64-NEXT:    ld a1, 16(sp)
+; FUCHSIA-RISCV64-NEXT:    bne a0, a1, .LBB0_2
+; FUCHSIA-RISCV64-NEXT:  # %bb.1: # %SP_return
+; FUCHSIA-RISCV64-NEXT:    ld ra, 24(sp) # 8-byte Folded Reload
+; FUCHSIA-RISCV64-NEXT:    addi sp, sp, 32
+; FUCHSIA-RISCV64-NEXT:    ret
+; FUCHSIA-RISCV64-NEXT:  .LBB0_2: # %CallStackCheckFailBlk
+; FUCHSIA-RISCV64-NEXT:    call __stack_chk_fail@plt
+  %1 = alloca i32, align 4
+  call void @capture(ptr nonnull %1)
+  ret void
+}
+
+declare void @capture(ptr)