From 23bd0b37482a127c8f954ce7e068a507b9c1e09e Mon Sep 17 00:00:00 2001
From: iximeow <me@iximeow.net>
Date: Sun, 26 Sep 2021 00:40:03 -0700
Subject: fix unimplemented code paths panicking as unreachable

only in a64 decoding really; there wasn't an "Incomplete" error at the time, but now there is.
---
 src/armv7.rs     | 12 ++++++------
 src/armv8/a64.rs | 22 +++++++++++++---------
 2 files changed, 19 insertions(+), 15 deletions(-)

(limited to 'src')

diff --git a/src/armv7.rs b/src/armv7.rs
index 64c9a4d..5894bc4 100644
--- a/src/armv7.rs
+++ b/src/armv7.rs
@@ -2280,7 +2280,7 @@ impl Decoder<ARMv7> for InstDecoder {
                         }
                     }
                     _ => {
-                        unreachable!();
+                        unreachable!("op1 is two bits");
                     }
                 }
             } else {
@@ -2405,7 +2405,7 @@ impl Decoder<ARMv7> for InstDecoder {
                                     Operand::Reg(Reg::from_u8(R[1])),
                                 ];
                             }
-                            _ => { unreachable!("mul upcode: {:x}", op) }
+                            _ => { unreachable!("mul opcode is only three bits, got: {:x}", op) }
                         }
                     } else {
                     // |c o n d|0 0 0 u|x x x x x x x x x x x x x x x x|1 u u 1|x x x x|
@@ -2894,7 +2894,7 @@ impl Decoder<ARMv7> for InstDecoder {
                                     _ => { unreachable!("impossible bit pattern"); }
                                 }
                             }
-                            _ => { unreachable!(); }
+                            _ => { unreachable!("op is two bits"); }
                         }
                     }
                 } else {
@@ -3004,7 +3004,7 @@ impl Decoder<ARMv7> for InstDecoder {
                                                 inst.operands[3] = Operand::Nothing;
                                             }
                                             _ => {
-                                                unreachable!();
+                                                unreachable!("opcode is masked to two bits here");
                                             }
                                         }
                                     }
@@ -3248,7 +3248,7 @@ impl Decoder<ARMv7> for InstDecoder {
                                     return Ok(());
                                 }
                                 _ => {
-                                    unreachable!();
+                                    unreachable!("word masked to two bits");
                                 }
                             }
                         }
@@ -3695,7 +3695,7 @@ impl Decoder<ARMv7> for InstDecoder {
                 // low bit of 0b110 or 0b111 corresponds to high bit of op1
                 return Err(DecodeError::Incomplete);
             },
-            _ => { unreachable!(); }
+            _ => { unreachable!("opc category is three bits"); }
         }
         Ok(())
     }
diff --git a/src/armv8/a64.rs b/src/armv8/a64.rs
index 16ed9c5..68f2337 100644
--- a/src/armv8/a64.rs
+++ b/src/armv8/a64.rs
@@ -131,6 +131,7 @@ pub enum DecodeError {
     ExhaustedInput,
     InvalidOpcode,
     InvalidOperand,
+    IncompleteDecoder,
 }
 
 impl fmt::Display for DecodeError {
@@ -164,6 +165,7 @@ impl yaxpeax_arch::DecodeError for DecodeError {
             DecodeError::ExhaustedInput => "exhausted input",
             DecodeError::InvalidOpcode => "invalid opcode",
             DecodeError::InvalidOperand => "invalid operand",
+            DecodeError::IncompleteDecoder => "incomplete decoder",
         }
     }
 }
@@ -1089,7 +1091,7 @@ impl Decoder<ARMv8> for InstDecoder {
         match section {
             Section::DataProcessingSimd |
             Section::DataProcessingSimd2 => {
-                unreachable!();
+                return Err(DecodeError::IncompleteDecoder);
             }
             Section::Unallocated => {
                 inst.opcode = Opcode::Invalid;
@@ -1165,7 +1167,7 @@ impl Decoder<ARMv8> for InstDecoder {
                         },
                         0b001 => {
                             // Conditional compare (register/immediate)
-                            unimplemented!();
+                            return Err(DecodeError::IncompleteDecoder);
                         },
                         0b010 => {
                             // Conditional select
@@ -1243,7 +1245,7 @@ impl Decoder<ARMv8> for InstDecoder {
                             if ((word >> 30) & 1) == 0 {
                                 // X0X11010_110XXXXX_XXXXXXXX_XXXXXXXX
                                 // Data-processing (2 source)
-                                unimplemented!();
+                                return Err(DecodeError::IncompleteDecoder);
                             } else {
                                 // X1X11010_110XXXXX_XXXXXXXX_XXXXXXXX
                                 // Data-processing (1 source)
@@ -1256,7 +1258,7 @@ impl Decoder<ARMv8> for InstDecoder {
                                 // however, PAC (added in v8.3) says otherwise.
                                 match opcode2 {
                                     0b00000 => {
-                                        unimplemented!();
+                                        return Err(DecodeError::IncompleteDecoder);
                                     }
                                     0b00001 => {
                                         match opcode {
@@ -1290,14 +1292,14 @@ impl Decoder<ARMv8> for InstDecoder {
                                         }
                                     }
                                     _ => {
-                                        unimplemented!();
+                                        return Err(DecodeError::IncompleteDecoder);
                                     }
                                 }
                             }
                         },
                         _ => {
                             // Data processing (3 source)
-                            unimplemented!();
+                            return Err(DecodeError::IncompleteDecoder);
                         }
                     }
                 } else {
@@ -1730,9 +1732,10 @@ impl Decoder<ARMv8> for InstDecoder {
                         } else {
                             inst.opcode = Opcode::Invalid;
                         }
-                        unimplemented!("decode Rd: {}, Rn: {}, imms: {}, Rm: {}, No0: {}", Rd, Rn, imms, Rm, No0);
+                        // eprintln!("decode Rd: {}, Rn: {}, imms: {}, Rm: {}, No0: {}", Rd, Rn, imms, Rm, No0);
+                        return Err(DecodeError::IncompleteDecoder);
                     }
-                    _ => { unreachable!() }
+                    _ => { unreachable!("group is three bits") }
                 }
             },
             Section::LoadStore => {
@@ -2058,7 +2061,8 @@ impl Decoder<ARMv8> for InstDecoder {
                         // load/store register pair (post-indexed)
                         // V == 1
                         let opc_L = ((word >> 22) & 1) | ((word >> 29) & 0x6);
-                        unreachable!("C3.3.15 V==1, opc_L: {}", opc_L);
+                        // eprintln!("C3.3.15 V==1, opc_L: {}", opc_L);
+                        return Err(DecodeError::IncompleteDecoder);
                     },
                     0b10010 => {
                         // load/store register pair (offset)
-- 
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