[Qemu-devel] [PATCH] target-arm: Don't decode old cp15 WFI instructions on v7 cores

[Qemu-devel] [PATCH] target-arm: Don't decode old cp15 WFI instructions on v7 cores

[Peter Maydell]

In v7 of the ARM architecture, WFI (wait for interrupt) is a first-class
instruction, but in previous versions this functionality was provided
via a cp15 coprocessor register. Add correct feature checks to the
decoding of the cp15 WFI instructions so that they behave correctly
for newer cores. In particular, the old 0,c7,c8,2 encoding used on
ARM940 has been reused for VA-to-PA translation in v6 and v7.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
This patch stands alone as a fix to target-arm; it's a prerequisite
for Adam's VA->PA translation patch, because otherwise attempting a
user-read translation will get you a WFI instead...

 target-arm/translate.c |   35 ++++++++++++++++++++++++++++++-----
 1 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/target-arm/translate.c b/target-arm/translate.c
index dbd958b..baa1256 100644
--- a/target-arm/translate.c
+++ b/target-arm/translate.c
@@ -2538,13 +2538,38 @@ static int disas_cp15_insn(CPUState *env, DisasContext *s, uint32_t insn)
     if (IS_USER(s) && !cp15_user_ok(insn)) {
         return 1;
     }
-    if ((insn & 0x0fff0fff) == 0x0e070f90
-        || (insn & 0x0fff0fff) == 0x0e070f58) {
-        /* Wait for interrupt.  */
-        gen_set_pc_im(s->pc);
-        s->is_jmp = DISAS_WFI;
+
+    /* Pre-v7 versions of the architecture implemented WFI via coprocessor
+     * instructions rather than a separate instruction.
+     */
+    if ((insn & 0x0fff0fff) == 0x0e070f90) {
+        /* 0,c7,c0,4: Standard v6 WFI (also used in some pre-v6 cores).
+         * In v7, this must NOP.
+         */
+        if (!arm_feature(env, ARM_FEATURE_V7)) {
+            /* Wait for interrupt.  */
+            gen_set_pc_im(s->pc);
+            s->is_jmp = DISAS_WFI;
+        }
         return 0;
     }
+
+    if ((insn & 0x0fff0fff) == 0x0e070f58) {
+        /* 0,c7,c8,2: Not all pre-v6 cores implemented this WFI,
+         * so this is slightly over-broad.
+         */
+        if (!arm_feature(env, ARM_FEATURE_V6)) {
+            /* Wait for interrupt.  */
+            gen_set_pc_im(s->pc);
+            s->is_jmp = DISAS_WFI;
+            return 0;
+        }
+        /* Otherwise fall through to handle via helper function.
+         * In particular, on v7 and some v6 cores this is one of
+         * the VA-PA registers.
+         */
+    }
+
     rd = (insn >> 12) & 0xf;
 
     if (cp15_tls_load_store(env, s, insn, rd))
-- 
1.7.1

[Qemu-devel] Re: [PATCH] target-arm: Don't decode old cp15 WFI instructions on v7 cores

[Adam Lackorzynski]

On Fri Feb 25, 2011 at 15:04:12 +0000, Peter Maydell wrote:
> In v7 of the ARM architecture, WFI (wait for interrupt) is a first-class
> instruction, but in previous versions this functionality was provided
> via a cp15 coprocessor register. Add correct feature checks to the
> decoding of the cp15 WFI instructions so that they behave correctly
> for newer cores. In particular, the old 0,c7,c8,2 encoding used on
> ARM940 has been reused for VA-to-PA translation in v6 and v7.
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

Reviewed-by: Adam Lackorzynski <adam@os.inf.tu-dresden.de>

> ---
> This patch stands alone as a fix to target-arm; it's a prerequisite
> for Adam's VA->PA translation patch, because otherwise attempting a
> user-read translation will get you a WFI instead...

Thanks, (un)fortunately I never triggered this case in my setup.



Adam
-- 
Adam                 adam@os.inf.tu-dresden.de
  Lackorzynski         http://os.inf.tu-dresden.de/~adam/

Re: [Qemu-devel] [PATCH] target-arm: Don't decode old cp15 WFI instructions on v7 cores

[Aurelien Jarno]

On Fri, Feb 25, 2011 at 03:04:12PM +0000, Peter Maydell wrote:
> In v7 of the ARM architecture, WFI (wait for interrupt) is a first-class
> instruction, but in previous versions this functionality was provided
> via a cp15 coprocessor register. Add correct feature checks to the
> decoding of the cp15 WFI instructions so that they behave correctly
> for newer cores. In particular, the old 0,c7,c8,2 encoding used on
> ARM940 has been reused for VA-to-PA translation in v6 and v7.
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> This patch stands alone as a fix to target-arm; it's a prerequisite
> for Adam's VA->PA translation patch, because otherwise attempting a
> user-read translation will get you a WFI instead...
> 
>  target-arm/translate.c |   35 ++++++++++++++++++++++++++++++-----
>  1 files changed, 30 insertions(+), 5 deletions(-)

Thanks, applied.

> diff --git a/target-arm/translate.c b/target-arm/translate.c
> index dbd958b..baa1256 100644
> --- a/target-arm/translate.c
> +++ b/target-arm/translate.c
> @@ -2538,13 +2538,38 @@ static int disas_cp15_insn(CPUState *env, DisasContext *s, uint32_t insn)
>      if (IS_USER(s) && !cp15_user_ok(insn)) {
>          return 1;
>      }
> -    if ((insn & 0x0fff0fff) == 0x0e070f90
> -        || (insn & 0x0fff0fff) == 0x0e070f58) {
> -        /* Wait for interrupt.  */
> -        gen_set_pc_im(s->pc);
> -        s->is_jmp = DISAS_WFI;
> +
> +    /* Pre-v7 versions of the architecture implemented WFI via coprocessor
> +     * instructions rather than a separate instruction.
> +     */
> +    if ((insn & 0x0fff0fff) == 0x0e070f90) {
> +        /* 0,c7,c0,4: Standard v6 WFI (also used in some pre-v6 cores).
> +         * In v7, this must NOP.
> +         */
> +        if (!arm_feature(env, ARM_FEATURE_V7)) {
> +            /* Wait for interrupt.  */
> +            gen_set_pc_im(s->pc);
> +            s->is_jmp = DISAS_WFI;
> +        }
>          return 0;
>      }
> +
> +    if ((insn & 0x0fff0fff) == 0x0e070f58) {
> +        /* 0,c7,c8,2: Not all pre-v6 cores implemented this WFI,
> +         * so this is slightly over-broad.
> +         */
> +        if (!arm_feature(env, ARM_FEATURE_V6)) {
> +            /* Wait for interrupt.  */
> +            gen_set_pc_im(s->pc);
> +            s->is_jmp = DISAS_WFI;
> +            return 0;
> +        }
> +        /* Otherwise fall through to handle via helper function.
> +         * In particular, on v7 and some v6 cores this is one of
> +         * the VA-PA registers.
> +         */
> +    }
> +
>      rd = (insn >> 12) & 0xf;
>  
>      if (cp15_tls_load_store(env, s, insn, rd))
> -- 
> 1.7.1
> 
> 
> 

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net