[PATCH] target/arm: Don't decode insns in the XScale/iWMMXt space as cp insns

[PATCH] target/arm: Don't decode insns in the XScale/iWMMXt space as cp insns

[Peter Maydell]

In commit cd8be50e58f63413c0 we converted the A32 coprocessor
insns to decodetree. This accidentally broke XScale/iWMMXt insns,
because it moved the handling of "cp insns which are handled
by looking up the cp register in the hashtable" from after the
call to the legacy disas_xscale_insn() decode to before it,
with the result that all XScale/iWMMXt insns now UNDEF.

Update valid_cp() so that it knows that on XScale cp 0 and 1
are not standard coprocessor instructions; this will cause
the decodetree trans_ functions to ignore them, so that
execution will correctly get through to the legacy decode again.

Cc: qemu-stable@nongnu.org
Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
With this Guenter's test image now successfully boots
and shuts down again.
---
 target/arm/translate.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/target/arm/translate.c b/target/arm/translate.c
index f5acd32e76a..528b93dffa2 100644
--- a/target/arm/translate.c
+++ b/target/arm/translate.c
@@ -5282,7 +5282,14 @@ static bool valid_cp(DisasContext *s, int cp)
      * only cp14 and cp15 are valid, and other values aren't considered
      * to be in the coprocessor-instruction space at all. v8M still
      * permits coprocessors 0..7.
+     * For XScale, we must not decode the XScale cp0, cp1 space as
+     * a standard coprocessor insn, because we want to fall through to
+     * the legacy disas_xscale_insn() decoder after decodetree is done.
      */
+    if (arm_dc_feature(s, ARM_FEATURE_XSCALE) && (cp == 0 || cp == 1)) {
+        return false;
+    }
+
     if (arm_dc_feature(s, ARM_FEATURE_V8) &&
         !arm_dc_feature(s, ARM_FEATURE_M)) {
         return cp >= 14;
-- 
2.20.1

Re: [PATCH] target/arm: Don't decode insns in the XScale/iWMMXt space as cp insns

[Richard Henderson]

On 1/8/21 9:51 AM, Peter Maydell wrote:
> In commit cd8be50e58f63413c0 we converted the A32 coprocessor
> insns to decodetree. This accidentally broke XScale/iWMMXt insns,
> because it moved the handling of "cp insns which are handled
> by looking up the cp register in the hashtable" from after the
> call to the legacy disas_xscale_insn() decode to before it,
> with the result that all XScale/iWMMXt insns now UNDEF.
> 
> Update valid_cp() so that it knows that on XScale cp 0 and 1
> are not standard coprocessor instructions; this will cause
> the decodetree trans_ functions to ignore them, so that
> execution will correctly get through to the legacy decode again.
> 
> Cc: qemu-stable@nongnu.org
> Reported-by: Guenter Roeck <linux@roeck-us.net>
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> With this Guenter's test image now successfully boots
> and shuts down again.
> ---

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~

Re: [PATCH] target/arm: Don't decode insns in the XScale/iWMMXt space as cp insns

[Guenter Roeck]

On 1/8/21 11:51 AM, Peter Maydell wrote:
> In commit cd8be50e58f63413c0 we converted the A32 coprocessor
> insns to decodetree. This accidentally broke XScale/iWMMXt insns,
> because it moved the handling of "cp insns which are handled
> by looking up the cp register in the hashtable" from after the
> call to the legacy disas_xscale_insn() decode to before it,
> with the result that all XScale/iWMMXt insns now UNDEF.
> 
> Update valid_cp() so that it knows that on XScale cp 0 and 1
> are not standard coprocessor instructions; this will cause
> the decodetree trans_ functions to ignore them, so that
> execution will correctly get through to the legacy decode again.
> 
> Cc: qemu-stable@nongnu.org
> Reported-by: Guenter Roeck <linux@roeck-us.net>
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> With this Guenter's test image now successfully boots
> and shuts down again.
> ---

Thanks a lot for the fix!

Tested-by: Guenter Roeck <linux@roeck-us.net>

>  target/arm/translate.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/target/arm/translate.c b/target/arm/translate.c
> index f5acd32e76a..528b93dffa2 100644
> --- a/target/arm/translate.c
> +++ b/target/arm/translate.c
> @@ -5282,7 +5282,14 @@ static bool valid_cp(DisasContext *s, int cp)
>       * only cp14 and cp15 are valid, and other values aren't considered
>       * to be in the coprocessor-instruction space at all. v8M still
>       * permits coprocessors 0..7.
> +     * For XScale, we must not decode the XScale cp0, cp1 space as
> +     * a standard coprocessor insn, because we want to fall through to
> +     * the legacy disas_xscale_insn() decoder after decodetree is done.
>       */
> +    if (arm_dc_feature(s, ARM_FEATURE_XSCALE) && (cp == 0 || cp == 1)) {
> +        return false;
> +    }
> +
>      if (arm_dc_feature(s, ARM_FEATURE_V8) &&
>          !arm_dc_feature(s, ARM_FEATURE_M)) {
>          return cp >= 14;
>