The ARMv5 architecture didn't specify detailed per-feature ID
registers. Now that we're using the MVFR0 register fields to
gate the existence of VFP instructions, we need to set up
the correct values in the cpu->isar structure so that we still
provide an FPU to the guest.

This fixes a regression in the arm926 and arm1026 CPUs, which
are the only ones that both have VFP and are ARMv5 or earlier.
This regression was introduced by the VFP refactoring, and more
specifically by commits 1120827fa182f0e76 and 266bd25c485597c,
which accidentally disabled VFP short-vector support and
double-precision support on these CPUs.

Reported-by: Christophe Lyon <christophe.lyon@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Fixes: 1120827fa182f0e
Fixes: 266bd25c485597c
Fixes: https://bugs.launchpad.net/qemu/+bug/1836192
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
---
v1->v2: just move the arm1026_initfn() part up a few lines;
this seems trivial so I've retained the reviewed-by tags.

 target/arm/cpu.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/target/arm/cpu.c b/target/arm/cpu.c
index e75a64a25a4..05b78ba2662 100644
--- a/target/arm/cpu.c
+++ b/target/arm/cpu.c
@@ -1666,6 +1666,12 @@ static void arm926_initfn(Object *obj)
      * set the field to indicate Jazelle support within QEMU.
      */
     cpu->isar.id_isar1 = FIELD_DP32(cpu->isar.id_isar1, ID_ISAR1, JAZELLE, 1);
+    /*
+     * Similarly, we need to set MVFR0 fields to enable double precision
+     * and short vector support even though ARMv5 doesn't have this register.
+     */
+    cpu->isar.mvfr0 = FIELD_DP32(cpu->isar.mvfr0, MVFR0, FPSHVEC, 1);
+    cpu->isar.mvfr0 = FIELD_DP32(cpu->isar.mvfr0, MVFR0, FPDP, 1);
 }
 
 static void arm946_initfn(Object *obj)
@@ -1702,6 +1708,12 @@ static void arm1026_initfn(Object *obj)
      * set the field to indicate Jazelle support within QEMU.
      */
     cpu->isar.id_isar1 = FIELD_DP32(cpu->isar.id_isar1, ID_ISAR1, JAZELLE, 1);
+    /*
+     * Similarly, we need to set MVFR0 fields to enable double precision
+     * and short vector support even though ARMv5 doesn't have this register.
+     */
+    cpu->isar.mvfr0 = FIELD_DP32(cpu->isar.mvfr0, MVFR0, FPSHVEC, 1);
+    cpu->isar.mvfr0 = FIELD_DP32(cpu->isar.mvfr0, MVFR0, FPDP, 1);
 
     {
         /* The 1026 had an IFAR at c6,c0,0,1 rather than the ARMv6 c6,c0,0,2 */
-- 
2.20.1

On Thu, 11 Jul 2019 at 15:12, Peter Maydell <peter.maydell@linaro.org> wrote:
>
> The ARMv5 architecture didn't specify detailed per-feature ID
> registers. Now that we're using the MVFR0 register fields to
> gate the existence of VFP instructions, we need to set up
> the correct values in the cpu->isar structure so that we still
> provide an FPU to the guest.
>
> This fixes a regression in the arm926 and arm1026 CPUs, which
> are the only ones that both have VFP and are ARMv5 or earlier.
> This regression was introduced by the VFP refactoring, and more
> specifically by commits 1120827fa182f0e76 and 266bd25c485597c,
> which accidentally disabled VFP short-vector support and
> double-precision support on these CPUs.
>
> Reported-by: Christophe Lyon <christophe.lyon@linaro.org>
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> Fixes: 1120827fa182f0e
> Fixes: 266bd25c485597c
> Fixes: https://bugs.launchpad.net/qemu/+bug/1836192
> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
> Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
> ---
> v1->v2: just move the arm1026_initfn() part up a few lines;
> this seems trivial so I've retained the reviewed-by tags.
>

For v1:
Tested-by: Christophe Lyon <christophe.lyon@linaro.org>

Works for me, thanks!

>  target/arm/cpu.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/target/arm/cpu.c b/target/arm/cpu.c
> index e75a64a25a4..05b78ba2662 100644
> --- a/target/arm/cpu.c
> +++ b/target/arm/cpu.c
> @@ -1666,6 +1666,12 @@ static void arm926_initfn(Object *obj)
>       * set the field to indicate Jazelle support within QEMU.
>       */
>      cpu->isar.id_isar1 = FIELD_DP32(cpu->isar.id_isar1, ID_ISAR1, JAZELLE, 1);
> +    /*
> +     * Similarly, we need to set MVFR0 fields to enable double precision
> +     * and short vector support even though ARMv5 doesn't have this register.
> +     */
> +    cpu->isar.mvfr0 = FIELD_DP32(cpu->isar.mvfr0, MVFR0, FPSHVEC, 1);
> +    cpu->isar.mvfr0 = FIELD_DP32(cpu->isar.mvfr0, MVFR0, FPDP, 1);
>  }
>
>  static void arm946_initfn(Object *obj)
> @@ -1702,6 +1708,12 @@ static void arm1026_initfn(Object *obj)
>       * set the field to indicate Jazelle support within QEMU.
>       */
>      cpu->isar.id_isar1 = FIELD_DP32(cpu->isar.id_isar1, ID_ISAR1, JAZELLE, 1);
> +    /*
> +     * Similarly, we need to set MVFR0 fields to enable double precision
> +     * and short vector support even though ARMv5 doesn't have this register.
> +     */
> +    cpu->isar.mvfr0 = FIELD_DP32(cpu->isar.mvfr0, MVFR0, FPSHVEC, 1);
> +    cpu->isar.mvfr0 = FIELD_DP32(cpu->isar.mvfr0, MVFR0, FPDP, 1);
>
>      {
>          /* The 1026 had an IFAR at c6,c0,0,1 rather than the ARMv6 c6,c0,0,2 */
> --
> 2.20.1
>