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target/arm: Convert ERET, ERETAA, ERETAB to decodetree 
Convert the exception-return insns ERET, ERETA and ERETB to
decodetree. These were the last insns left in the legacy
decoder function disas_uncond_reg_b(), which allows us to
remove it.

The old decoder explicitly decoded the DRPS instruction,
only in order to call unallocated_encoding() on it, exactly
as would have happened if it hadn't decoded it. This is
because this insn always UNDEFs unless the CPU is in
halting-debug state, which we don't emulate. So we list
the pattern in a comment in a64.decode, but don't actively
decode it.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20230512144106.3608981-21-peter.maydell@linaro.org
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pm215 committed May 18, 2023
1 parent c990fde commit 442c9d6
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Showing 2 changed files with 63 additions and 108 deletions.
8 changes: 8 additions & 0 deletions target/arm/tcg/a64.decode
View file
Expand Up @@ -142,3 +142,11 @@ RETA 1101011 0010 11111 00001 m:1 11111 11111 &reta # RETAA, RETAB
&bra rn rm m
BRA 1101011 1000 11111 00001 m:1 rn:5 rm:5 &bra # BRAA, BRAB
BLRA 1101011 1001 11111 00001 m:1 rn:5 rm:5 &bra # BLRAA, BLRAB

ERET 1101011 0100 11111 000000 11111 00000
ERETA 1101011 0100 11111 00001 m:1 11111 11111 &reta # ERETAA, ERETAB

# We don't need to decode DRPS because it always UNDEFs except when
# the processor is in halting debug state (which we don't implement).
# The pattern is listed here as documentation.
# DRPS 1101011 0101 11111 000000 11111 00000
163 changes: 55 additions & 108 deletions target/arm/tcg/translate-a64.c
View file
Expand Up @@ -1539,6 +1539,61 @@ static bool trans_BLRA(DisasContext *s, arg_bra *a)
return true;
}

static bool trans_ERET(DisasContext *s, arg_ERET *a)
{
TCGv_i64 dst;

if (s->current_el == 0) {
return false;
}
if (s->fgt_eret) {
gen_exception_insn_el(s, 0, EXCP_UDEF, 0, 2);
return true;
}
dst = tcg_temp_new_i64();
tcg_gen_ld_i64(dst, cpu_env,
offsetof(CPUARMState, elr_el[s->current_el]));

if (tb_cflags(s->base.tb) & CF_USE_ICOUNT) {
gen_io_start();
}

gen_helper_exception_return(cpu_env, dst);
/* Must exit loop to check un-masked IRQs */
s->base.is_jmp = DISAS_EXIT;
return true;
}

static bool trans_ERETA(DisasContext *s, arg_reta *a)
{
TCGv_i64 dst;

if (!dc_isar_feature(aa64_pauth, s)) {
return false;
}
if (s->current_el == 0) {
return false;
}
/* The FGT trap takes precedence over an auth trap. */
if (s->fgt_eret) {
gen_exception_insn_el(s, 0, EXCP_UDEF, a->m ? 3 : 2, 2);
return true;
}
dst = tcg_temp_new_i64();
tcg_gen_ld_i64(dst, cpu_env,
offsetof(CPUARMState, elr_el[s->current_el]));

dst = auth_branch_target(s, dst, cpu_X[31], !a->m);
if (tb_cflags(s->base.tb) & CF_USE_ICOUNT) {
gen_io_start();
}

gen_helper_exception_return(cpu_env, dst);
/* Must exit loop to check un-masked IRQs */
s->base.is_jmp = DISAS_EXIT;
return true;
}

/* HINT instruction group, including various allocated HINTs */
static void handle_hint(DisasContext *s, uint32_t insn,
unsigned int op1, unsigned int op2, unsigned int crm)
Expand Down Expand Up @@ -2307,111 +2362,6 @@ static void disas_exc(DisasContext *s, uint32_t insn)
}
}

/* Unconditional branch (register)
* 31 25 24 21 20 16 15 10 9 5 4 0
* +---------------+-------+-------+-------+------+-------+
* | 1 1 0 1 0 1 1 | opc | op2 | op3 | Rn | op4 |
* +---------------+-------+-------+-------+------+-------+
*/
static void disas_uncond_b_reg(DisasContext *s, uint32_t insn)
{
unsigned int opc, op2, op3, rn, op4;
TCGv_i64 dst;
TCGv_i64 modifier;

opc = extract32(insn, 21, 4);
op2 = extract32(insn, 16, 5);
op3 = extract32(insn, 10, 6);
rn = extract32(insn, 5, 5);
op4 = extract32(insn, 0, 5);

if (op2 != 0x1f) {
goto do_unallocated;
}

switch (opc) {
case 0:
case 1:
case 2:
case 8:
case 9:
/*
* BR, BLR, RET, RETAA, RETAB, BRAAZ, BRABZ, BLRAAZ, BLRABZ,
* BRAA, BLRAA: handled in decodetree
*/
goto do_unallocated;

case 4: /* ERET */
if (s->current_el == 0) {
goto do_unallocated;
}
switch (op3) {
case 0: /* ERET */
if (op4 != 0) {
goto do_unallocated;
}
if (s->fgt_eret) {
gen_exception_insn_el(s, 0, EXCP_UDEF, syn_erettrap(op3), 2);
return;
}
dst = tcg_temp_new_i64();
tcg_gen_ld_i64(dst, cpu_env,
offsetof(CPUARMState, elr_el[s->current_el]));
break;

case 2: /* ERETAA */
case 3: /* ERETAB */
if (!dc_isar_feature(aa64_pauth, s)) {
goto do_unallocated;
}
if (rn != 0x1f || op4 != 0x1f) {
goto do_unallocated;
}
/* The FGT trap takes precedence over an auth trap. */
if (s->fgt_eret) {
gen_exception_insn_el(s, 0, EXCP_UDEF, syn_erettrap(op3), 2);
return;
}
dst = tcg_temp_new_i64();
tcg_gen_ld_i64(dst, cpu_env,
offsetof(CPUARMState, elr_el[s->current_el]));
if (s->pauth_active) {
modifier = cpu_X[31];
if (op3 == 2) {
gen_helper_autia(dst, cpu_env, dst, modifier);
} else {
gen_helper_autib(dst, cpu_env, dst, modifier);
}
}
break;

default:
goto do_unallocated;
}
if (tb_cflags(s->base.tb) & CF_USE_ICOUNT) {
gen_io_start();
}

gen_helper_exception_return(cpu_env, dst);
/* Must exit loop to check un-masked IRQs */
s->base.is_jmp = DISAS_EXIT;
return;

case 5: /* DRPS */
if (op3 != 0 || op4 != 0 || rn != 0x1f) {
goto do_unallocated;
} else {
unallocated_encoding(s);
}
return;

default:
do_unallocated:
unallocated_encoding(s);
return;
}
}

/* Branches, exception generating and system instructions */
static void disas_b_exc_sys(DisasContext *s, uint32_t insn)
{
Expand All @@ -2427,9 +2377,6 @@ static void disas_b_exc_sys(DisasContext *s, uint32_t insn)
disas_exc(s, insn);
}
break;
case 0x6b: /* Unconditional branch (register) */
disas_uncond_b_reg(s, insn);
break;
default:
unallocated_encoding(s);
break;
Expand Down

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