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authorPeter Maydell <peter.maydell@linaro.org>2015-07-06 10:05:44 +0100
committerPeter Maydell <peter.maydell@linaro.org>2015-07-06 10:05:44 +0100
commit049e24a191c212d9468db84169197887f2c91586 (patch)
treea3e485b8175ffb43636ec5556ff2e4ebc558a6d0
parenta7ffaf5c96e26820edffa94eeac766fe60bfdd31 (diff)
downloadqemu-arm-049e24a191c212d9468db84169197887f2c91586.tar.gz
target-arm: Split DISAS_YIELD from DISAS_WFE
Currently we use DISAS_WFE for both WFE and YIELD instructions. This is functionally correct because at the moment both of them are implemented as "yield this CPU back to the top level loop so another CPU has a chance to run". However it's rather confusing that YIELD ends up calling HELPER(wfe), and if we ever want to implement real behaviour for WFE and SEV it's likely to trip us up. Split out the yield codepath to use DISAS_YIELD and a new HELPER(yield) function, and have HELPER(wfe) call HELPER(yield). Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Message-id: 1435672316-3311-2-git-send-email-peter.maydell@linaro.org Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
-rw-r--r--target-arm/helper.h1
-rw-r--r--target-arm/op_helper.c18
-rw-r--r--target-arm/translate-a64.c6
-rw-r--r--target-arm/translate.h1
4 files changed, 23 insertions, 3 deletions
diff --git a/target-arm/helper.h b/target-arm/helper.h
index fc885dea43..827b33dfec 100644
--- a/target-arm/helper.h
+++ b/target-arm/helper.h
@@ -50,6 +50,7 @@ DEF_HELPER_2(exception_internal, void, env, i32)
DEF_HELPER_4(exception_with_syndrome, void, env, i32, i32, i32)
DEF_HELPER_1(wfi, void, env)
DEF_HELPER_1(wfe, void, env)
+DEF_HELPER_1(yield, void, env)
DEF_HELPER_1(pre_hvc, void, env)
DEF_HELPER_2(pre_smc, void, env, i32)
diff --git a/target-arm/op_helper.c b/target-arm/op_helper.c
index 7fa32c4707..663c05d1d2 100644
--- a/target-arm/op_helper.c
+++ b/target-arm/op_helper.c
@@ -323,13 +323,25 @@ void HELPER(wfi)(CPUARMState *env)
void HELPER(wfe)(CPUARMState *env)
{
- CPUState *cs = CPU(arm_env_get_cpu(env));
-
- /* Don't actually halt the CPU, just yield back to top
+ /* This is a hint instruction that is semantically different
+ * from YIELD even though we currently implement it identically.
+ * Don't actually halt the CPU, just yield back to top
* level loop. This is not going into a "low power state"
* (ie halting until some event occurs), so we never take
* a configurable trap to a different exception level.
*/
+ HELPER(yield)(env);
+}
+
+void HELPER(yield)(CPUARMState *env)
+{
+ ARMCPU *cpu = arm_env_get_cpu(env);
+ CPUState *cs = CPU(cpu);
+
+ /* This is a non-trappable hint instruction that generally indicates
+ * that the guest is currently busy-looping. Yield control back to the
+ * top level loop so that a more deserving VCPU has a chance to run.
+ */
cs->exception_index = EXCP_YIELD;
cpu_loop_exit(cs);
}
diff --git a/target-arm/translate-a64.c b/target-arm/translate-a64.c
index e077f2dc30..689f2be896 100644
--- a/target-arm/translate-a64.c
+++ b/target-arm/translate-a64.c
@@ -1199,6 +1199,8 @@ static void handle_hint(DisasContext *s, uint32_t insn,
s->is_jmp = DISAS_WFI;
return;
case 1: /* YIELD */
+ s->is_jmp = DISAS_YIELD;
+ return;
case 2: /* WFE */
s->is_jmp = DISAS_WFE;
return;
@@ -11107,6 +11109,10 @@ void gen_intermediate_code_internal_a64(ARMCPU *cpu,
gen_a64_set_pc_im(dc->pc);
gen_helper_wfe(cpu_env);
break;
+ case DISAS_YIELD:
+ gen_a64_set_pc_im(dc->pc);
+ gen_helper_yield(cpu_env);
+ break;
case DISAS_WFI:
/* This is a special case because we don't want to just halt the CPU
* if trying to debug across a WFI.
diff --git a/target-arm/translate.h b/target-arm/translate.h
index bcdcf11718..9ab978fb75 100644
--- a/target-arm/translate.h
+++ b/target-arm/translate.h
@@ -103,6 +103,7 @@ static inline int default_exception_el(DisasContext *s)
#define DISAS_WFE 7
#define DISAS_HVC 8
#define DISAS_SMC 9
+#define DISAS_YIELD 10
#ifdef TARGET_AARCH64
void a64_translate_init(void);