diff mbox series

[v2,2/2] sparc: Prevent stfsr from directly following floating-point instruction

Message ID 20240115145345.3389246-3-cederman@gaisler.com
State Committed
Commit 82a35070ec35616074343b8c4ffe6b1cff7e2793
Headers
Series [v2] sparc: Force calculation that raises exception |

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Commit Message

Daniel Cederman Jan. 15, 2024, 2:53 p.m. UTC 
  On LEON, if the stfsr instruction is immediately following a floating-point
operation instruction in a running program, with no other instruction in
between the two, the stfsr might behave as if the order was reversed
between the two instructions and the stfsr occurred before the
floating-point operation.

Add a nop instruction before the stfsr to prevent this from happening.

Signed-off-by: Daniel Cederman <cederman@gaisler.com>
---
 sysdeps/sparc/fpu/fpu_control.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

Comments

Adhemerval Zanella Netto Jan. 16, 2024, 1:59 p.m. UTC | #1 
On 15/01/24 11:53, Daniel Cederman wrote:
> On LEON, if the stfsr instruction is immediately following a floating-point
> operation instruction in a running program, with no other instruction in
> between the two, the stfsr might behave as if the order was reversed
> between the two instructions and the stfsr occurred before the
> floating-point operation.
> 
> Add a nop instruction before the stfsr to prevent this from happening.
> 
> Signed-off-by: Daniel Cederman <cederman@gaisler.com>

LGTM, thanks.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> ---
>  sysdeps/sparc/fpu/fpu_control.h | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/sysdeps/sparc/fpu/fpu_control.h b/sysdeps/sparc/fpu/fpu_control.h
> index dd18789573..48368a7ce1 100644
> --- a/sysdeps/sparc/fpu/fpu_control.h
> +++ b/sysdeps/sparc/fpu/fpu_control.h
> @@ -61,7 +61,12 @@ typedef unsigned long int fpu_control_t;
>  # define _FPU_GETCW(cw) __asm__ __volatile__ ("stx %%fsr,%0" : "=m" (*&cw))
>  # define _FPU_SETCW(cw) __asm__ __volatile__ ("ldx %0,%%fsr" : : "m" (*&cw))
>  #else
> -# define _FPU_GETCW(cw) __asm__ __volatile__ ("st %%fsr,%0" : "=m" (*&cw))
> +# ifdef __leon__
> +   /* Prevent stfsr from being placed directly after other fp instruction.  */
> +#  define _FPU_GETCW(cw) __asm__ __volatile__ ("nop; st %%fsr,%0" : "=m" (*&cw))
> +# else
> +#  define _FPU_GETCW(cw) __asm__ __volatile__ ("st %%fsr,%0" : "=m" (*&cw))
> +# endif
>  # define _FPU_SETCW(cw) __asm__ __volatile__ ("ld %0,%%fsr" : : "m" (*&cw))
>  #endif
>
diff mbox series

Patch

diff --git a/sysdeps/sparc/fpu/fpu_control.h b/sysdeps/sparc/fpu/fpu_control.h
index dd18789573..48368a7ce1 100644
--- a/sysdeps/sparc/fpu/fpu_control.h
+++ b/sysdeps/sparc/fpu/fpu_control.h
@@ -61,7 +61,12 @@  typedef unsigned long int fpu_control_t;
 # define _FPU_GETCW(cw) __asm__ __volatile__ ("stx %%fsr,%0" : "=m" (*&cw))
 # define _FPU_SETCW(cw) __asm__ __volatile__ ("ldx %0,%%fsr" : : "m" (*&cw))
 #else
-# define _FPU_GETCW(cw) __asm__ __volatile__ ("st %%fsr,%0" : "=m" (*&cw))
+# ifdef __leon__
+   /* Prevent stfsr from being placed directly after other fp instruction.  */
+#  define _FPU_GETCW(cw) __asm__ __volatile__ ("nop; st %%fsr,%0" : "=m" (*&cw))
+# else
+#  define _FPU_GETCW(cw) __asm__ __volatile__ ("st %%fsr,%0" : "=m" (*&cw))
+# endif
 # define _FPU_SETCW(cw) __asm__ __volatile__ ("ld %0,%%fsr" : : "m" (*&cw))
 #endif