fix(m68k): correct SR register read (#2161)

The SR register in the `CPUM68KState` struct does not contain the value
of the lower 5 flags. To compute them, we must OR the CCR values with
the SR register to get the true SR value.

bindings/rust/src/tests/m68k.rs

@@ -20,3 +20,22 @@ fn test_move_to_sr() {
     let sr = uc.reg_read(RegisterM68K::SR).unwrap();
     assert_eq!(sr, 0x2700);
 }
+
+#[test]
+fn test_sr_contains_flags() {
+    let code = [
+        0x76, 0xed, // moveq #-19, %d3
+    ];
+
+    let mut uc = uc_common_setup(Arch::M68K, Mode::BIG_ENDIAN, None, &code, ());
+
+    uc.emu_start(CODE_START, CODE_START + code.len() as u64, 0, 0)
+        .unwrap();
+
+    let d3 = uc.reg_read(RegisterM68K::D3).unwrap();
+    assert_eq!(d3, 0xffffffed);
+
+    let sr = uc.reg_read(RegisterM68K::SR).unwrap();
+    let is_negative = sr & 0x8 == 0x8;
+    assert!(is_negative, "SR should contain negative flag");
+}

qemu/m68k.h

@@ -1372,6 +1372,7 @@
 #define helper_bitrev helper_bitrev_m68k
 #define helper_ff1 helper_ff1_m68k
 #define helper_sats helper_sats_m68k
+#define cpu_m68k_get_sr cpu_m68k_get_sr_m68k
 #define cpu_m68k_set_sr cpu_m68k_set_sr_m68k
 #define helper_set_sr helper_set_sr_m68k
 #define helper_mac_move helper_mac_move_m68k

qemu/target/m68k/cpu.h

@@ -183,6 +183,7 @@ int cpu_m68k_signal_handler(int host_signum, void *pinfo,
                            void *puc);
 uint32_t cpu_m68k_get_ccr(CPUM68KState *env);
 void cpu_m68k_set_ccr(CPUM68KState *env, uint32_t);
+uint32_t cpu_m68k_get_sr(CPUM68KState *env);
 void cpu_m68k_set_sr(CPUM68KState *env, uint32_t);
 void cpu_m68k_set_fpcr(CPUM68KState *env, uint32_t val);
 

qemu/target/m68k/helper.c

@@ -591,6 +591,10 @@ uint32_t HELPER(sats)(uint32_t val, uint32_t v)
     return val;
 }
 
+uint32_t cpu_m68k_get_sr(CPUM68KState *env) {
+    return env->sr | cpu_m68k_get_ccr(env);
+}
+
 void cpu_m68k_set_sr(CPUM68KState *env, uint32_t sr)
 {
     env->sr = sr & 0xffe0;

qemu/target/m68k/unicorn.c

@@ -72,7 +72,8 @@ uc_err reg_read(void *_env, int mode, unsigned int regid, void *value,
             break;
         case UC_M68K_REG_SR:
             CHECK_REG_TYPE(uint32_t);
-            *(uint32_t *)value = env->sr;
+            env->cc_op = CC_OP_FLAGS;
+            *(uint32_t *)value = cpu_m68k_get_sr(env);
             break;
         case UC_M68K_REG_CR_SFC:
             CHECK_REG_TYPE(uint32_t);

symbols.sh

@@ -5749,6 +5749,7 @@ m68k_cpu_tlb_fill \
 helper_bitrev \
 helper_ff1 \
 helper_sats \
+cpu_m68k_get_sr \
 cpu_m68k_set_sr \
 helper_set_sr \
 helper_mac_move \

tests/unit/test_m68k.c

@@ -37,4 +37,29 @@ static void test_move_to_sr(void)
     OK(uc_close(uc));
 }
 
-TEST_LIST = {{"test_move_to_sr", test_move_to_sr}, {NULL, NULL}};
+static void test_sr_contains_flags(void)
+{
+    uc_engine *uc;
+    uint8_t code[] = {
+        0x76, 0xed, // moveq #-19, %d3
+    };
+
+    uint32_t d3, sr;
+
+    uc_common_setup(&uc, UC_ARCH_M68K, UC_MODE_BIG_ENDIAN, code, sizeof(code),
+                    UC_CPU_M68K_M68000);
+
+    OK(uc_emu_start(uc, code_start, code_start + sizeof(code), 0, 0));
+
+    OK(uc_reg_read(uc, UC_M68K_REG_D3, &d3));
+    OK(uc_reg_read(uc, UC_M68K_REG_SR, &sr));
+
+    TEST_CHECK(d3 == 0xFFFFFFED);
+    TEST_CHECK((sr & 0x8) /* N flag */ == 0x8);
+
+    OK(uc_close(uc));
+}
+
+TEST_LIST = {{"test_move_to_sr", test_move_to_sr},
+             {"test_sr_contains_flags", test_sr_contains_flags},
+             {NULL, NULL}};