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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>
This commit is contained in:
Mark Cave-Ayland 2021-03-08 12:11:55 +00:00 committed by Laurent Vivier
parent 469949c902
commit a9431a03f7
3 changed files with 7 additions and 1 deletions
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1
target/m68k/cpu.c
View File

@ -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);
}
/*

2
target/m68k/cpu.h
View File

@ -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)

5
target/m68k/op_helper.c
View File

@ -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");