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target/arm: Convert exception generation instructions to decodetree 
Convert the exception generation instructions SVC, HVC, SMC, BRK and
HLT to decodetree.

The old decoder decoded the halting-debug insnns DCPS1, DCPS2 and
DCPS3 just in order to then make them UNDEF; as with DRPS, we don't
bother to decode them, but document the patterns in a64.decode.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20230602155223.2040685-8-peter.maydell@linaro.org
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pm215 committed Jun 19, 2023
1 parent 6e3c804 commit a97d3c1
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15 changes: 15 additions & 0 deletions target/arm/tcg/a64.decode
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Expand Up @@ -215,3 +215,18 @@ MSR_i_SVCR 1101 0101 0000 0 011 0100 0 mask:2 imm:1 011 11111
SYS 1101 0101 00 l:1 01 op1:3 crn:4 crm:4 op2:3 rt:5 op0=1
SYS 1101 0101 00 l:1 10 op1:3 crn:4 crm:4 op2:3 rt:5 op0=2
SYS 1101 0101 00 l:1 11 op1:3 crn:4 crm:4 op2:3 rt:5 op0=3

# Exception generation

@i16 .... .... ... imm:16 ... .. &i
SVC 1101 0100 000 ................ 000 01 @i16
HVC 1101 0100 000 ................ 000 10 @i16
SMC 1101 0100 000 ................ 000 11 @i16
BRK 1101 0100 001 ................ 000 00 @i16
HLT 1101 0100 010 ................ 000 00 @i16
# These insns always UNDEF unless in halting debug state, which
# we don't implement. So we don't need to decode them. The patterns
# are listed here as documentation.
# DCPS1 1101 0100 101 ................ 000 01 @i16
# DCPS2 1101 0100 101 ................ 000 10 @i16
# DCPS3 1101 0100 101 ................ 000 11 @i16
167 changes: 61 additions & 106 deletions target/arm/tcg/translate-a64.c
View file
Expand Up @@ -2313,119 +2313,77 @@ static bool trans_SYS(DisasContext *s, arg_SYS *a)
return true;
}

/* Exception generation
*
* 31 24 23 21 20 5 4 2 1 0
* +-----------------+-----+------------------------+-----+----+
* | 1 1 0 1 0 1 0 0 | opc | imm16 | op2 | LL |
* +-----------------------+------------------------+----------+
*/
static void disas_exc(DisasContext *s, uint32_t insn)
static bool trans_SVC(DisasContext *s, arg_i *a)
{
int opc = extract32(insn, 21, 3);
int op2_ll = extract32(insn, 0, 5);
int imm16 = extract32(insn, 5, 16);
uint32_t syndrome;
/*
* For SVC, HVC and SMC we advance the single-step state
* machine before taking the exception. This is architecturally
* mandated, to ensure that single-stepping a system call
* instruction works properly.
*/
uint32_t syndrome = syn_aa64_svc(a->imm);
if (s->fgt_svc) {
gen_exception_insn_el(s, 0, EXCP_UDEF, syndrome, 2);
return true;
}
gen_ss_advance(s);
gen_exception_insn(s, 4, EXCP_SWI, syndrome);
return true;
}

switch (opc) {
case 0:
/* For SVC, HVC and SMC we advance the single-step state
* machine before taking the exception. This is architecturally
* mandated, to ensure that single-stepping a system call
* instruction works properly.
*/
switch (op2_ll) {
case 1: /* SVC */
syndrome = syn_aa64_svc(imm16);
if (s->fgt_svc) {
gen_exception_insn_el(s, 0, EXCP_UDEF, syndrome, 2);
break;
}
gen_ss_advance(s);
gen_exception_insn(s, 4, EXCP_SWI, syndrome);
break;
case 2: /* HVC */
if (s->current_el == 0) {
unallocated_encoding(s);
break;
}
/* The pre HVC helper handles cases when HVC gets trapped
* as an undefined insn by runtime configuration.
*/
gen_a64_update_pc(s, 0);
gen_helper_pre_hvc(cpu_env);
gen_ss_advance(s);
gen_exception_insn_el(s, 4, EXCP_HVC, syn_aa64_hvc(imm16), 2);
break;
case 3: /* SMC */
if (s->current_el == 0) {
unallocated_encoding(s);
break;
}
gen_a64_update_pc(s, 0);
gen_helper_pre_smc(cpu_env, tcg_constant_i32(syn_aa64_smc(imm16)));
gen_ss_advance(s);
gen_exception_insn_el(s, 4, EXCP_SMC, syn_aa64_smc(imm16), 3);
break;
default:
unallocated_encoding(s);
break;
}
break;
case 1:
if (op2_ll != 0) {
unallocated_encoding(s);
break;
}
/* BRK */
gen_exception_bkpt_insn(s, syn_aa64_bkpt(imm16));
break;
case 2:
if (op2_ll != 0) {
unallocated_encoding(s);
break;
}
/* HLT. This has two purposes.
* Architecturally, it is an external halting debug instruction.
* Since QEMU doesn't implement external debug, we treat this as
* it is required for halting debug disabled: it will UNDEF.
* Secondly, "HLT 0xf000" is the A64 semihosting syscall instruction.
*/
if (semihosting_enabled(s->current_el == 0) && imm16 == 0xf000) {
gen_exception_internal_insn(s, EXCP_SEMIHOST);
} else {
unallocated_encoding(s);
}
break;
case 5:
if (op2_ll < 1 || op2_ll > 3) {
unallocated_encoding(s);
break;
}
/* DCPS1, DCPS2, DCPS3 */
static bool trans_HVC(DisasContext *s, arg_i *a)
{
if (s->current_el == 0) {
unallocated_encoding(s);
break;
default:
return true;
}
/*
* The pre HVC helper handles cases when HVC gets trapped
* as an undefined insn by runtime configuration.
*/
gen_a64_update_pc(s, 0);
gen_helper_pre_hvc(cpu_env);
/* Architecture requires ss advance before we do the actual work */
gen_ss_advance(s);
gen_exception_insn_el(s, 4, EXCP_HVC, syn_aa64_hvc(a->imm), 2);
return true;
}

static bool trans_SMC(DisasContext *s, arg_i *a)
{
if (s->current_el == 0) {
unallocated_encoding(s);
break;
return true;
}
gen_a64_update_pc(s, 0);
gen_helper_pre_smc(cpu_env, tcg_constant_i32(syn_aa64_smc(a->imm)));
/* Architecture requires ss advance before we do the actual work */
gen_ss_advance(s);
gen_exception_insn_el(s, 4, EXCP_SMC, syn_aa64_smc(a->imm), 3);
return true;
}

/* Branches, exception generating and system instructions */
static void disas_b_exc_sys(DisasContext *s, uint32_t insn)
static bool trans_BRK(DisasContext *s, arg_i *a)
{
switch (extract32(insn, 25, 7)) {
case 0x6a: /* Exception generation / System */
if (insn & (1 << 24)) {
unallocated_encoding(s);
} else {
disas_exc(s, insn);
}
break;
default:
gen_exception_bkpt_insn(s, syn_aa64_bkpt(a->imm));
return true;
}

static bool trans_HLT(DisasContext *s, arg_i *a)
{
/*
* HLT. This has two purposes.
* Architecturally, it is an external halting debug instruction.
* Since QEMU doesn't implement external debug, we treat this as
* it is required for halting debug disabled: it will UNDEF.
* Secondly, "HLT 0xf000" is the A64 semihosting syscall instruction.
*/
if (semihosting_enabled(s->current_el == 0) && a->imm == 0xf000) {
gen_exception_internal_insn(s, EXCP_SEMIHOST);
} else {
unallocated_encoding(s);
break;
}
return true;
}

/*
Expand Down Expand Up @@ -14188,9 +14146,6 @@ static bool btype_destination_ok(uint32_t insn, bool bt, int btype)
static void disas_a64_legacy(DisasContext *s, uint32_t insn)
{
switch (extract32(insn, 25, 4)) {
case 0xa: case 0xb: /* Branch, exception generation and system insns */
disas_b_exc_sys(s, insn);
break;
case 0x4:
case 0x6:
case 0xc:
Expand Down

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