[RISCV] Use the thread local stack protector for Android targets (llvm#87672)

Android supports per thread stack protectors that are individually
managed and
initialized, which can provide stronger protections than using the
global stack
protector cookie. This patch matches the convention for other
architectures
targeting Android platforms.

Author: ilovepi

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -21052,6 +21052,12 @@ Value *RISCVTargetLowering::getIRStackGuard(IRBuilderBase &IRB) const {
   if (Subtarget.isTargetFuchsia())
     return useTpOffset(IRB, -0x10);
 
+  // Android provides a fixed TLS slot for the stack cookie. See the definition
+  // of TLS_SLOT_STACK_GUARD in
+  // https://android.googlesource.com/platform/bionic/+/main/libc/platform/bionic/tls_defines.h
+  if (Subtarget.isTargetAndroid())
+    return useTpOffset(IRB, -0x18);
+
   return TargetLowering::getIRStackGuard(IRB);
 }
 

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

@@ -50,21 +50,18 @@ define void @func() sspreq nounwind {
 ; ANDROID-RISCV64:       # %bb.0:
 ; ANDROID-RISCV64-NEXT:    addi sp, sp, -32
 ; ANDROID-RISCV64-NEXT:    sd ra, 24(sp) # 8-byte Folded Spill
-; ANDROID-RISCV64-NEXT:    sd s0, 16(sp) # 8-byte Folded Spill
-; ANDROID-RISCV64-NEXT:    lui s0, %hi(__stack_chk_guard)
-; ANDROID-RISCV64-NEXT:    ld a0, %lo(__stack_chk_guard)(s0)
-; ANDROID-RISCV64-NEXT:    sd a0, 8(sp)
-; ANDROID-RISCV64-NEXT:    addi a0, sp, 4
+; ANDROID-RISCV64-NEXT:    ld a0, -24(tp)
+; ANDROID-RISCV64-NEXT:    sd a0, 16(sp)
+; ANDROID-RISCV64-NEXT:    addi a0, sp, 12
 ; ANDROID-RISCV64-NEXT:    call capture
-; ANDROID-RISCV64-NEXT:    ld a0, %lo(__stack_chk_guard)(s0)
-; ANDROID-RISCV64-NEXT:    ld a1, 8(sp)
+; ANDROID-RISCV64-NEXT:    ld a0, -24(tp)
+; ANDROID-RISCV64-NEXT:    ld a1, 16(sp)
 ; ANDROID-RISCV64-NEXT:    bne a0, a1, .LBB0_2
-; ANDROID-RISCV64-NEXT:  # %bb.1:
+; ANDROID-RISCV64-NEXT:  # %bb.1: # %SP_return
 ; ANDROID-RISCV64-NEXT:    ld ra, 24(sp) # 8-byte Folded Reload
-; ANDROID-RISCV64-NEXT:    ld s0, 16(sp) # 8-byte Folded Reload
 ; ANDROID-RISCV64-NEXT:    addi sp, sp, 32
 ; ANDROID-RISCV64-NEXT:    ret
-; ANDROID-RISCV64-NEXT:  .LBB0_2:
+; ANDROID-RISCV64-NEXT:  .LBB0_2: # %CallStackCheckFailBlk
 ; ANDROID-RISCV64-NEXT:    call __stack_chk_fail
   %1 = alloca i32, align 4
   call void @capture(ptr %1)