From bf21b98498469066ece6933d8d7d724b63ac8c64 Mon Sep 17 00:00:00 2001
From: pjht <pterpstra@pterpstra.com>
Date: Sat, 9 Mar 2024 12:25:55 -0600
Subject: [PATCH] Fix PC displacement being treated as unsigned

---
 src/disas.rs        |  5 ++++-
 src/instruction.rs  |  2 +-
 src/m68k.rs         | 36 ++++++++++++++++++++++++++----------
 src/symbol.rs       |  9 ++++-----
 src/symbol_table.rs | 12 ++++++++++--
 5 files changed, 45 insertions(+), 19 deletions(-)

diff --git a/src/disas.rs b/src/disas.rs
index 710edad..97f7d2c 100644
--- a/src/disas.rs
+++ b/src/disas.rs
@@ -889,7 +889,10 @@ impl<T> Disasm<'_, T> {
             match misc_mode {
                 MiscMode::PcDisplacement => {
                     let pc = self.pc;
-                    Ok(EffectiveAddress::PcDisplacement(pc, self.read_prog_word()?))
+                    Ok(EffectiveAddress::PcDisplacement(
+                        pc,
+                        self.read_prog_word()? as i16,
+                    ))
                 }
                 MiscMode::PcIndex => {
                     let pc = self.pc;
diff --git a/src/instruction.rs b/src/instruction.rs
index 850cc27..2ef9a46 100644
--- a/src/instruction.rs
+++ b/src/instruction.rs
@@ -43,7 +43,7 @@ pub enum EffectiveAddress {
         idx: RegisterEffective,
         idx_size: Size,
     },
-    PcDisplacement(u32, u16),
+    PcDisplacement(u32, i16),
     PcIndex(u32, u8, RegisterEffective, Size),
     AbsoluteShort(u16),
     AbsoluteLong(u32),
diff --git a/src/m68k.rs b/src/m68k.rs
index 7c5d253..2388ba8 100644
--- a/src/m68k.rs
+++ b/src/m68k.rs
@@ -1381,7 +1381,11 @@ impl M68K {
                 self.read_address(address, size)
             }
             EffectiveAddress::PcDisplacement(pc, d) => {
-                let address = pc.wrapping_add(d.into());
+                let address = if d > 0 {
+                    pc.wrapping_add((d as u16).into())
+                } else {
+                    pc.wrapping_sub((-d as u16).into())
+                };
                 self.read_address(address, size)
             }
             EffectiveAddress::PcIndex(pc, displacement, idx, idx_size) => {
@@ -1518,10 +1522,13 @@ impl M68K {
                 self.store_mem_cycles = true;
             }
         }
-        let result = self.bus.read_byte(address, self.is_supervisor()).map_err(|_| DetailedBusError {
-            address,
-            cause: BusErrorCause::ReadingByte,
-        });
+        let result = self
+            .bus
+            .read_byte(address, self.is_supervisor())
+            .map_err(|_| DetailedBusError {
+                address,
+                cause: BusErrorCause::ReadingByte,
+            });
         if self.store_mem_cycles {
             self.stored_mem_cycles
                 .push(MemCycleInfo::ReadByte { address, result });
@@ -1588,10 +1595,13 @@ impl M68K {
                 self.store_mem_cycles = true;
             }
         }
-        let result = self.bus.read_word(address, self.is_supervisor()).map_err(|_| DetailedBusError {
-            address,
-            cause: BusErrorCause::ReadingWord,
-        });
+        let result = self
+            .bus
+            .read_word(address, self.is_supervisor())
+            .map_err(|_| DetailedBusError {
+                address,
+                cause: BusErrorCause::ReadingWord,
+            });
         if self.store_mem_cycles {
             self.stored_mem_cycles
                 .push(MemCycleInfo::ReadWord { address, result });
@@ -1674,7 +1684,13 @@ impl M68K {
                         .wrapping_sub((-d as u16).into()))
                 }
             }
-            EffectiveAddress::PcDisplacement(pc, d) => Ok(pc.wrapping_add(d.into())),
+            EffectiveAddress::PcDisplacement(pc, d) => {
+                if d > 0 {
+                    Ok(pc.wrapping_add((d as u16).into()))
+                } else {
+                    Ok(pc.wrapping_sub((-d as u16).into()))
+                }
+            },
             EffectiveAddress::AbsoluteShort(x) => Ok(u32::from(x)),
             EffectiveAddress::AbsoluteLong(x) => Ok(x),
             EffectiveAddress::DataReg(_)
diff --git a/src/symbol.rs b/src/symbol.rs
index f8bc521..f8ae4da 100644
--- a/src/symbol.rs
+++ b/src/symbol.rs
@@ -40,14 +40,13 @@ impl Symbol {
 impl Display for Symbol {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         if self.size == 0 {
-            f.write_fmt(format_args!(
-                "{:#010x} ({})",
-                self.value, self.sect_name
-            ))
+            f.write_fmt(format_args!("{:#010x} ({})", self.value, self.sect_name))
         } else {
             f.write_fmt(format_args!(
                 "{:#010x}..{:#010x} ({})",
-                self.value, self.value+self.size, self.sect_name
+                self.value,
+                self.value + self.size,
+                self.sect_name
             ))
         }
     }
diff --git a/src/symbol_table.rs b/src/symbol_table.rs
index f88dd2a..26a34e7 100644
--- a/src/symbol_table.rs
+++ b/src/symbol_table.rs
@@ -62,7 +62,10 @@ impl SymbolTable {
         let mut file = ElfStream::<AnyEndian, _>::open_stream(File::open(path)?)?;
         let (sect_headers, shstrtab) = file.section_headers_with_strtab()?;
         let shstrtab = shstrtab.unwrap();
-        let sect_names = sect_headers.iter().map(|sect| shstrtab.get(sect.sh_name as usize).unwrap().to_string()).collect::<Vec<_>>();
+        let sect_names = sect_headers
+            .iter()
+            .map(|sect| shstrtab.get(sect.sh_name as usize).unwrap().to_string())
+            .collect::<Vec<_>>();
         let (symtab, symstrtab) = file
             .symbol_table()?
             .ok_or_else(|| anyhow!("No symbol table in {}", path))?;
@@ -73,7 +76,12 @@ impl SymbolTable {
             .map(|sym| {
                 (
                     symstrtab.get(sym.st_name as usize).unwrap().to_string(),
-                    Symbol::new(&sym, sect_names.get(sym.st_shndx as usize).map_or_else(|| "UNKNOWN".to_string(), |x| x.to_string())),
+                    Symbol::new(
+                        &sym,
+                        sect_names
+                            .get(sym.st_shndx as usize)
+                            .map_or_else(|| "UNKNOWN".to_string(), |x| x.to_string()),
+                    ),
                 )
             })
             .collect::<HashMap<_, _>>();