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Re: [PATCH 02/13] target/riscv: Extend pc for runtime pc write


From: LIU Zhiwei
Subject: Re: [PATCH 02/13] target/riscv: Extend pc for runtime pc write
Date: Tue, 2 Nov 2021 09:48:01 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0


On 2021/11/1 下午6:33, Richard Henderson wrote:
On 11/1/21 6:01 AM, LIU Zhiwei wrote:
In some cases, we must restore the guest PC to the address of the start of the TB, such as when the instruction counter hit zero. So extend pc register
according to current xlen for these cases.

Signed-off-by: LIU Zhiwei <zhiwei_liu@c-sky.com>
---
  target/riscv/cpu.c        | 20 +++++++++++++++++---
  target/riscv/cpu.h        |  2 ++
  target/riscv/cpu_helper.c |  2 +-
  3 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index 7d53125dbc..7eefd4f6a6 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -319,7 +319,12 @@ static void riscv_cpu_set_pc(CPUState *cs, vaddr value)
  {
      RISCVCPU *cpu = RISCV_CPU(cs);
      CPURISCVState *env = &cpu->env;
-    env->pc = value;
+
+    if (cpu_get_xl(env) == MXL_RV32) {
+        env->pc = (int32_t)value;
+    } else {
+        env->pc = value;
+    }
  }

Good.

  static void riscv_cpu_synchronize_from_tb(CPUState *cs,
@@ -327,7 +332,12 @@ static void riscv_cpu_synchronize_from_tb(CPUState *cs,
  {
      RISCVCPU *cpu = RISCV_CPU(cs);
      CPURISCVState *env = &cpu->env;
-    env->pc = tb->pc;
+
+    if (cpu_get_xl(env) == MXL_RV32) {
+        env->pc = (int32_t)tb->pc;
+    } else {
+        env->pc = tb->pc;
+    }

Bad, since TB->PC should be extended properly.
Though this waits on a change to cpu_get_tb_cpu_state.

Should the env->pc always hold the sign-extend result? In cpu_get_tb_cpu_state, we just truncate to the XLEN bits.

Thanks,
Zhiwei


@@ -348,7 +358,11 @@ static bool riscv_cpu_has_work(CPUState *cs)
  void restore_state_to_opc(CPURISCVState *env, TranslationBlock *tb,
                            target_ulong *data)
  {
-    env->pc = data[0];
+   if (cpu_get_xl(env) == MXL_RV32) {
+        env->pc = (int32_t)data[0];
+    } else {
+        env->pc = data[0];
+    }

Likewise.


r~



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