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From: Fabien Chouteau <chouteau@adacore.com>
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Date: Mon, 7 Dec 2015 12:35:52 +0100
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Subject: Re: [Qemu-devel] [PATCH] sparc: allow CASA with ASI 0xa from user
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To: Alex Zuepke <azu@sysgo.de>, qemu-devel@nongnu.org

Hello Alex,

Thanks for your patch! I have a couple of comments. 

On 12/04/2015 04:01 PM, Alex Zuepke wrote:
> LEON3 allows the CASA instruction to be used from user space
> if the ASI is set to 0xa (user data).
> 
> Signed-off-by: Alex Zuepke <azu@sysgo.de>
> ---
>  target-sparc/translate.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/target-sparc/translate.c b/target-sparc/translate.c
> index 41a3319..63440dd 100644
> --- a/target-sparc/translate.c
> +++ b/target-sparc/translate.c
> @@ -5097,7 +5097,8 @@ static void disas_sparc_insn(DisasContext * dc, unsigned int insn)
>                      if (IS_IMM) {
>                          goto illegal_insn;
>                      }
> -                    if (!supervisor(dc)) {
> +                    /* LEON3 allows CASA from user space with ASI 0xa */

Since this is a LEON3 specific feature, when you check the ASI you
should also check CPU_FEATURE_CASA.

> +                    if ((GET_FIELD(insn, 19, 26) != 0xa) && !supervisor(dc)) {
>                          goto priv_insn;
>                      }

That would give you something like this:

diff --git a/target-sparc/translate.c b/target-sparc/translate.c
index 41a3319..b93faea 100644
--- a/target-sparc/translate.c
+++ b/target-sparc/translate.c
@@ -2463,6 +2463,9 @@ static void gen_faligndata(TCGv dst, TCGv gsr, TCGv s1, TCGv s2)
 }
 #endif

+#define IU_FEATURE(dc, FEATURE)                            \
+    (((dc)->def->features & CPU_FEATURE_ ## FEATURE))
+
 #define CHECK_IU_FEATURE(dc, FEATURE)                      \
     if (!((dc)->def->features & CPU_FEATURE_ ## FEATURE))  \
         goto illegal_insn;
@@ -5097,7 +5100,11 @@ static void disas_sparc_insn(DisasContext * dc, unsigned int insn)
                     if (IS_IMM) {
                         goto illegal_insn;
                     }
-                    if (!supervisor(dc)) {
+
+                    /* LEON3 allows CASA from user space with ASI 0xa */
+                    if (!((IU_FEATURE(dc, CASA) &&
+                           (GET_FIELD(insn, 19, 26) == 0xa))
+                          || supervisor(dc))) {
                         goto priv_insn;
                     }
 #endif


to be tested of course ;)

Regards,