thumb SIMD encoding should have returned Incomplete

2 files changed, 11 insertions, 0 deletions

diff --git a/CHANGELOG b/CHANGELOG
index b552484..20c885d 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -44,6 +44,16 @@ as well as thumb2 fixes from @brandonros:
 
 thank you for the patches!
 
+additionally, one of the cases where thumb-mode SIMD instructions should have
+been rejected with DecodeError::Incomplete instead fell through to report a
+successful decode result of the provided instruction. this now results in
+DecodeError::Incomplete as expected.
+
+when decoding into an instruction multiple times (such as `Decoder::decode_into`)
+the provided instruction would be left in an incoherent state mostly consiting
+of its previous data. when decoding as through `Decoder::decode`, the returned
+instruction had opcode `Invalid`.
+
 ## 0.4.0
 
 * ARMv7 and A64 `Opcode` and `Operand` are now `#[non_exhaustive]`.
diff --git a/src/armv7/thumb.rs b/src/armv7/thumb.rs
index 439c3a6..b8d1192 100644
--- a/src/armv7/thumb.rs
+++ b/src/armv7/thumb.rs
@@ -2212,6 +2212,7 @@ pub fn decode_into<T: Reader<<ARMv7 as Arch>::Address, <ARMv7 as Arch>::Word>>(d
                         } else {
                             // `Advanced SIMD element or structure load/store instructions`
                             // (`A7-273`)
+                            return Err(DecodeError::Incomplete);
                         }
                     } else {
                         // this section is a merger of three tables: