[Qemu-devel] [PULL 20/62] target-arm: Clean up handling of AArch64 PSTATE

[Peter Maydell]

The env->pstate field is a little odd since it doesn't strictly
speaking represent an architectural register. However it's convenient
for QEMU to use it to hold the various PSTATE architectural bits
in the same format the architecture specifies for SPSR registers
(since this is the same format the kernel uses for signal handlers
and the KVM register). Add some structure to how we deal with it:
 * document what env->pstate is
 * add some #defines for various bits in it
 * add helpers for reading/writing it taking account of caching
   of NZCV, and use them where appropriate
 * reset it on startup

Signed-off-by: Peter Maydell <address@hidden>
Message-id: address@hidden
Reviewed-by: Christoffer Dall <address@hidden>
---
 linux-user/signal.c        |  6 ++--
 target-arm/cpu.c           |  6 ++++
 target-arm/cpu.h           | 70 ++++++++++++++++++++++++++++++++++++++--------
 target-arm/gdbstub64.c     |  4 +--
 target-arm/translate-a64.c | 12 ++++----
 5 files changed, 78 insertions(+), 20 deletions(-)

diff --git a/linux-user/signal.c b/linux-user/signal.c
index 7751c47..4e7148a 100644
--- a/linux-user/signal.c
+++ b/linux-user/signal.c
@@ -1171,7 +1171,7 @@ static int target_setup_sigframe(struct 
target_rt_sigframe *sf,
     }
     __put_user(env->xregs[31], &sf->uc.tuc_mcontext.sp);
     __put_user(env->pc, &sf->uc.tuc_mcontext.pc);
-    __put_user(env->pstate, &sf->uc.tuc_mcontext.pstate);
+    __put_user(pstate_read(env), &sf->uc.tuc_mcontext.pstate);
 
     __put_user(/*current->thread.fault_address*/ 0,
             &sf->uc.tuc_mcontext.fault_address);
@@ -1210,6 +1210,7 @@ static int target_restore_sigframe(CPUARMState *env,
     struct target_aux_context *aux =
         (struct target_aux_context *)sf->uc.tuc_mcontext.__reserved;
     uint32_t magic, size;
+    uint64_t pstate;
 
     target_to_host_sigset(&set, &sf->uc.tuc_sigmask);
     sigprocmask(SIG_SETMASK, &set, NULL);
@@ -1220,7 +1221,8 @@ static int target_restore_sigframe(CPUARMState *env,
 
     __get_user(env->xregs[31], &sf->uc.tuc_mcontext.sp);
     __get_user(env->pc, &sf->uc.tuc_mcontext.pc);
-    __get_user(env->pstate, &sf->uc.tuc_mcontext.pstate);
+    __get_user(pstate, &sf->uc.tuc_mcontext.pstate);
+    pstate_write(env, pstate);
 
     __get_user(magic, &aux->fpsimd.head.magic);
     __get_user(size, &aux->fpsimd.head.size);
diff --git a/target-arm/cpu.c b/target-arm/cpu.c
index 8288c7d..408d207 100644
--- a/target-arm/cpu.c
+++ b/target-arm/cpu.c
@@ -89,6 +89,12 @@ static void arm_cpu_reset(CPUState *s)
     if (arm_feature(env, ARM_FEATURE_AARCH64)) {
         /* 64 bit CPUs always start in 64 bit mode */
         env->aarch64 = 1;
+#if defined(CONFIG_USER_ONLY)
+        env->pstate = PSTATE_MODE_EL0t;
+#else
+        env->pstate = PSTATE_D | PSTATE_A | PSTATE_I | PSTATE_F
+            | PSTATE_MODE_EL1h;
+#endif
     }
 
 #if defined(CONFIG_USER_ONLY)
diff --git a/target-arm/cpu.h b/target-arm/cpu.h
index c6c19e9..3af4ed3 100644
--- a/target-arm/cpu.h
+++ b/target-arm/cpu.h
@@ -113,8 +113,15 @@ typedef struct CPUARMState {
     /* Regs for A64 mode.  */
     uint64_t xregs[32];
     uint64_t pc;
-    /* TODO: pstate doesn't correspond to an architectural register;
-     * it would be better modelled as the underlying fields.
+    /* PSTATE isn't an architectural register for ARMv8. However, it is
+     * convenient for us to assemble the underlying state into a 32 bit format
+     * identical to the architectural format used for the SPSR. (This is also
+     * what the Linux kernel's 'pstate' field in signal handlers and KVM's
+     * 'pstate' register are.) Of the PSTATE bits:
+     *  NZCV are kept in the split out env->CF/VF/NF/ZF, (which have the same
+     *    semantics as for AArch32, as described in the comments on each field)
+     *  nRW (also known as M[4]) is kept, inverted, in env->aarch64
+     *  all other bits are stored in their correct places in env->pstate
      */
     uint32_t pstate;
     uint32_t aarch64; /* 1 if CPU is in aarch64 state; inverse of PSTATE.nRW */
@@ -309,15 +316,6 @@ static inline bool is_a64(CPUARMState *env)
     return env->aarch64;
 }
 
-#define PSTATE_N_SHIFT 3
-#define PSTATE_N  (1 << PSTATE_N_SHIFT)
-#define PSTATE_Z_SHIFT 2
-#define PSTATE_Z  (1 << PSTATE_Z_SHIFT)
-#define PSTATE_C_SHIFT 1
-#define PSTATE_C  (1 << PSTATE_C_SHIFT)
-#define PSTATE_V_SHIFT 0
-#define PSTATE_V  (1 << PSTATE_V_SHIFT)
-
 /* you can call this signal handler from your SIGBUS and SIGSEGV
    signal handlers to inform the virtual CPU of exceptions. non zero
    is returned if the signal was handled by the virtual CPU.  */
@@ -352,6 +350,56 @@ int cpu_arm_handle_mmu_fault (CPUARMState *env, 
target_ulong address, int rw,
 /* Execution state bits.  MRS read as zero, MSR writes ignored.  */
 #define CPSR_EXEC (CPSR_T | CPSR_IT | CPSR_J)
 
+/* Bit definitions for ARMv8 SPSR (PSTATE) format.
+ * Only these are valid when in AArch64 mode; in
+ * AArch32 mode SPSRs are basically CPSR-format.
+ */
+#define PSTATE_M (0xFU)
+#define PSTATE_nRW (1U << 4)
+#define PSTATE_F (1U << 6)
+#define PSTATE_I (1U << 7)
+#define PSTATE_A (1U << 8)
+#define PSTATE_D (1U << 9)
+#define PSTATE_IL (1U << 20)
+#define PSTATE_SS (1U << 21)
+#define PSTATE_V (1U << 28)
+#define PSTATE_C (1U << 29)
+#define PSTATE_Z (1U << 30)
+#define PSTATE_N (1U << 31)
+#define PSTATE_NZCV (PSTATE_N | PSTATE_Z | PSTATE_C | PSTATE_V)
+#define CACHED_PSTATE_BITS (PSTATE_NZCV)
+/* Mode values for AArch64 */
+#define PSTATE_MODE_EL3h 13
+#define PSTATE_MODE_EL3t 12
+#define PSTATE_MODE_EL2h 9
+#define PSTATE_MODE_EL2t 8
+#define PSTATE_MODE_EL1h 5
+#define PSTATE_MODE_EL1t 4
+#define PSTATE_MODE_EL0t 0
+
+/* Return the current PSTATE value. For the moment we don't support 32<->64 bit
+ * interprocessing, so we don't attempt to sync with the cpsr state used by
+ * the 32 bit decoder.
+ */
+static inline uint32_t pstate_read(CPUARMState *env)
+{
+    int ZF;
+
+    ZF = (env->ZF == 0);
+    return (env->NF & 0x80000000) | (ZF << 30)
+        | (env->CF << 29) | ((env->VF & 0x80000000) >> 3)
+        | env->pstate;
+}
+
+static inline void pstate_write(CPUARMState *env, uint32_t val)
+{
+    env->ZF = (~val) & PSTATE_Z;
+    env->NF = val;
+    env->CF = (val >> 29) & 1;
+    env->VF = (val << 3) & 0x80000000;
+    env->pstate = val & ~CACHED_PSTATE_BITS;
+}
+
 /* Return the current CPSR value.  */
 uint32_t cpsr_read(CPUARMState *env);
 /* Set the CPSR.  Note that some bits of mask must be all-set or all-clear.  */
diff --git a/target-arm/gdbstub64.c b/target-arm/gdbstub64.c
index 7cb6a7c..e8a8295 100644
--- a/target-arm/gdbstub64.c
+++ b/target-arm/gdbstub64.c
@@ -37,7 +37,7 @@ int aarch64_cpu_gdb_read_register(CPUState *cs, uint8_t 
*mem_buf, int n)
         return gdb_get_reg64(mem_buf, env->pc);
         break;
     case 33:
-        return gdb_get_reg32(mem_buf, env->pstate);
+        return gdb_get_reg32(mem_buf, pstate_read(env));
     }
     /* Unknown register.  */
     return 0;
@@ -65,7 +65,7 @@ int aarch64_cpu_gdb_write_register(CPUState *cs, uint8_t 
*mem_buf, int n)
         return 8;
     case 33:
         /* CPSR */
-        env->pstate = tmp;
+        pstate_write(env, tmp);
         return 4;
     }
     /* Unknown register.  */
diff --git a/target-arm/translate-a64.c b/target-arm/translate-a64.c
index f120088..932b601 100644
--- a/target-arm/translate-a64.c
+++ b/target-arm/translate-a64.c
@@ -67,6 +67,7 @@ void aarch64_cpu_dump_state(CPUState *cs, FILE *f,
 {
     ARMCPU *cpu = ARM_CPU(cs);
     CPUARMState *env = &cpu->env;
+    uint32_t psr = pstate_read(env);
     int i;
 
     cpu_fprintf(f, "PC=%016"PRIx64"  SP=%016"PRIx64"\n",
@@ -79,11 +80,12 @@ void aarch64_cpu_dump_state(CPUState *cs, FILE *f,
             cpu_fprintf(f, " ");
         }
     }
-    cpu_fprintf(f, "PSTATE=%c%c%c%c\n",
-        env->pstate & PSTATE_N ? 'n' : '.',
-        env->pstate & PSTATE_Z ? 'z' : '.',
-        env->pstate & PSTATE_C ? 'c' : '.',
-        env->pstate & PSTATE_V ? 'v' : '.');
+    cpu_fprintf(f, "PSTATE=%08x (flags %c%c%c%c)\n",
+                psr,
+                psr & PSTATE_N ? 'N' : '-',
+                psr & PSTATE_Z ? 'Z' : '-',
+                psr & PSTATE_C ? 'C' : '-',
+                psr & PSTATE_V ? 'V' : '-');
     cpu_fprintf(f, "\n");
 }
 
-- 
1.8.5