[PATCH] D23312: [Thumb] Validate branch target for CBZ/CBNZ instructions.

[Prakhar Bahuguna via llvm-commits]

prakhar updated this revision to Diff 67495.
prakhar added a comment.

Immediate operand is 6 bits and should have cleared LSB.


https://reviews.llvm.org/D23312

Files:
  lib/Target/ARM/AsmParser/ARMAsmParser.cpp
  lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
  test/MC/ARM/thumb-cb-negative-offsets.s
  test/MC/ARM/thumb-diagnostics.s

Index: test/MC/ARM/thumb-diagnostics.s
===================================================================
--- test/MC/ARM/thumb-diagnostics.s
+++ test/MC/ARM/thumb-diagnostics.s
@@ -235,6 +235,23 @@
 @ CHECK-ERRORS: error: branch target out of range
 
 @------------------------------------------------------------------------------
+@ CBZ/CBNZ - out of range immediates for branches
+ at ------------------------------------------------------------------------------
+
+        cbz    r0, #-2
+        cbz    r0, #0
+        cbz    r0, #17
+        cbnz   r0, #126
+        cbnz   r0, #128
+
+@ CHECK-ERRORS-V7M: error: branch target out of range
+@ CHECK-ERRORS-V7M: error: invalid operand for instruction
+@ CHECK-ERRORS-V7M: error: branch target out of range
+@ CHECK-ERRORS-V8: error: branch target out of range
+@ CHECK-ERRORS-V8: error: invalid operand for instruction
+@ CHECK-ERRORS-V8: error: branch target out of range
+
+ at ------------------------------------------------------------------------------
 @ SEV/WFE/WFI/YIELD - are not supported pre v6M or v6T2
 @------------------------------------------------------------------------------
         sev
Index: test/MC/ARM/thumb-cb-negative-offsets.s
===================================================================
--- /dev/null
+++ test/MC/ARM/thumb-cb-negative-offsets.s
@@ -0,0 +1,19 @@
+@ RUN: not llvm-mc -triple thumbv7m-none-eabi      -filetype=obj -o /dev/null %s 2>&1 | FileCheck %s
+@ RUN: not llvm-mc -triple thumbv8m.base-none-eabi -filetype=obj -o /dev/null %s 2>&1 | FileCheck %s
+
+label0:
+  .word 4
+
+@ CHECK: out of range pc-relative fixup value
+  cbz r0, label0
+@ CHECK: out of range pc-relative fixup value
+  cbnz r0, label0
+
+@ CHECK: out of range pc-relative fixup value
+  cbz r0, label1
+@ CHECK: out of range pc-relative fixup value
+  cbnz r0, label1
+
+  .space 1000
+label1:
+  .word 4
Index: lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
===================================================================
--- lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
+++ lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
@@ -578,6 +578,11 @@
     // Offset by 4, and don't encode the low two bits.
     return ((Value - 4) >> 2) & 0xff;
   case ARM::fixup_arm_thumb_cb: {
+    // CB instructions can only branch to offsets in [0, 126] in multiples of 2
+    if (Ctx && ((int64_t)Value < 0 || Value > 0x3e || Value & 1)) {
+      Ctx->reportError(Fixup.getLoc(), "out of range pc-relative fixup value");
+      return 0;
+    }
     // Offset by 4 and don't encode the lower bit, which is always 0.
     // FIXME: diagnose if no Thumb2
     uint32_t Binary = (Value - 4) >> 1;
Index: lib/Target/ARM/AsmParser/ARMAsmParser.cpp
===================================================================
--- lib/Target/ARM/AsmParser/ARMAsmParser.cpp
+++ lib/Target/ARM/AsmParser/ARMAsmParser.cpp
@@ -6684,6 +6684,12 @@
       return Error(Operands[Op]->getStartLoc(), "branch target out of range");
     break;
   }
+  case ARM::tCBZ:
+  case ARM::tCBNZ: {
+    if (!static_cast<ARMOperand &>(*Operands[2]).isUnsignedOffset<6, 1>())
+      return Error(Operands[2]->getStartLoc(), "branch target out of range");
+    break;
+  }
   case ARM::MOVi16:
   case ARM::t2MOVi16:
   case ARM::t2MOVTi16:


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