[MC][ARM] Add range checking for Thumb2 resolved fixups.

When the branch target of a Thumb2 unconditional or conditonal branch is
resolved at assembly time, no range checking is performed on the result
leading to incorrect immediates. This change adds a range check:
+- 16 Megabytes for unconditional branches, +- 1 Megabyte for the
conditional branch.

Differential Revision: https://reviews.llvm.org/D46306

llvm-svn: 333997

1 files changed, 10 insertions, 0 deletions

diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
index 8df49903ffe..4a7bf8cc33c 100644
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
@@ -487,6 +487,11 @@ unsigned ARMAsmBackend::adjustFixupValue(const MCAssembler &Asm,
     return 0xffffff & ((Value - 8) >> 2);
   case ARM::fixup_t2_uncondbranch: {
     Value = Value - 4;
+    if (!isInt<25>(Value)) {
+      Ctx.reportError(Fixup.getLoc(), "Relocation out of range");
+      return 0;
+    }
+
     Value >>= 1; // Low bit is not encoded.
 
     uint32_t out = 0;
@@ -506,6 +511,11 @@ unsigned ARMAsmBackend::adjustFixupValue(const MCAssembler &Asm,
   }
   case ARM::fixup_t2_condbranch: {
     Value = Value - 4;
+    if (!isInt<21>(Value)) {
+      Ctx.reportError(Fixup.getLoc(), "Relocation out of range");
+      return 0;
+    }
+
     Value >>= 1; // Low bit is not encoded.
 
     uint64_t out = 0;