target/m68k: add M68K_FEATURE_UNALIGNED_DATA feature

According to the M68040UM Appendix D the requirement for data accesses to be
word aligned is only for the 68000, 68008 and 68010 CPUs. Later CPUs from the
68020 onwards will allow unaligned data accesses but at the cost of being less
efficient.

Add a new M68K_FEATURE_UNALIGNED_DATA feature to specify that data accesses are
not required to be word aligned, and don't perform the alignment on the stack
pointer when taking an exception if this feature is not selected.

This is required because the MacOS DAFB driver attempts to call an A-trap
with a byte-aligned stack pointer during initialisation and without this the
stack pointer is off by one when the A-trap returns.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210308121155.2476-4-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

diff --git a/target/m68k/cpu.c b/target/m68k/cpu.c
index 37d2ed9dc79c4ad8cb2898bf0e6f82f27f7334a5..a14874b4da284b9b963467980e06258ec5ed2db8 100644 (file)
--- a/target/m68k/cpu.c
+++ b/target/m68k/cpu.c
@@ -161,6 +161,7 @@ static void m68020_cpu_initfn(Object *obj)
     m68k_set_feature(env, M68K_FEATURE_CAS);
     m68k_set_feature(env, M68K_FEATURE_CHK2);
     m68k_set_feature(env, M68K_FEATURE_MSP);
+    m68k_set_feature(env, M68K_FEATURE_UNALIGNED_DATA);
 }
 
 /*

diff --git a/target/m68k/cpu.h b/target/m68k/cpu.h
index ce558e9b03e79358c2913031cfbccf6c5ef9febe..402c86c8769e4d127d2a81db13c2e87ec4b1d5a4 100644 (file)
--- a/target/m68k/cpu.h
+++ b/target/m68k/cpu.h
@@ -527,6 +527,8 @@ enum m68k_features {
     M68K_FEATURE_MOVEP,
     /* MOVEC insn. (from 68010) */
     M68K_FEATURE_MOVEC,
+    /* Unaligned data accesses (680[2346]0) */
+    M68K_FEATURE_UNALIGNED_DATA,
 };
 
 static inline int m68k_feature(CPUM68KState *env, int feature)

diff --git a/target/m68k/op_helper.c b/target/m68k/op_helper.c
index 5f981e5bf628fa84df25fb3704e7d448bbc4f10d..46ff81acc9f5ea6c7e65f2f3477f79c6babdb59a 100644 (file)
--- a/target/m68k/op_helper.c
+++ b/target/m68k/op_helper.c
@@ -348,7 +348,10 @@ static void m68k_interrupt_all(CPUM68KState *env, int is_hw)
     cpu_m68k_set_sr(env, sr);
     sp = env->aregs[7];
 
-    sp &= ~1;
+    if (!m68k_feature(env, M68K_FEATURE_UNALIGNED_DATA)) {
+        sp &= ~1;
+    }
+
     if (cs->exception_index == EXCP_ACCESS) {
         if (env->mmu.fault) {
             cpu_abort(cs, "DOUBLE MMU FAULT\n");