Our implementation of the FLOGB insn does the operations entirely
in the helper function, without needing to use fpu functions.
This means it needs to handle all the fp status flags itself.
We aren't setting float_flag_input_denormal_used when we
use (i.e. do not flush to zero) an input denormal, which means
that FPCR.IDC isn't set when it should be for FPCR.AH=1.
We missed this when we added float_flag_input_denormal_used
and made the fpu/ code set it.

Add the missing float_raise().

Cc: qemu-stable@nongnu.org
Fixes: d38a57a3f ("target/arm: Enable FEAT_AFP for '-cpu max'")
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 target/arm/tcg/sve_helper.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/target/arm/tcg/sve_helper.c b/target/arm/tcg/sve_helper.c
index 179cbd74fb..d884ba474f 100644
--- a/target/arm/tcg/sve_helper.c
+++ b/target/arm/tcg/sve_helper.c
@@ -5036,6 +5036,7 @@ static int16_t do_float16_logb_as_int(float16 a, float_status *s)
         if (frac != 0) {
             if (!get_flush_inputs_to_zero(s)) {
                 /* denormal: bias - fractional_zeros */
+                float_raise(float_flag_input_denormal_used, s);
                 return -15 - clz32(frac);
             }
             /* flush to zero */
@@ -5064,6 +5065,7 @@ static int32_t do_float32_logb_as_int(float32 a, float_status *s)
         if (frac != 0) {
             if (!get_flush_inputs_to_zero(s)) {
                 /* denormal: bias - fractional_zeros */
+                float_raise(float_flag_input_denormal_used, s);
                 return -127 - clz32(frac);
             }
             /* flush to zero */
@@ -5092,6 +5094,7 @@ static int64_t do_float64_logb_as_int(float64 a, float_status *s)
         if (frac != 0) {
             if (!get_flush_inputs_to_zero(s)) {
                 /* denormal: bias - fractional_zeros */
+                float_raise(float_flag_input_denormal_used, s);
                 return -1023 - clz64(frac);
             }
             /* flush to zero */
-- 
2.43.0

On 5/21/26 05:29, Peter Maydell wrote:
> Our implementation of the FLOGB insn does the operations entirely
> in the helper function, without needing to use fpu functions.
> This means it needs to handle all the fp status flags itself.
> We aren't setting float_flag_input_denormal_used when we
> use (i.e. do not flush to zero) an input denormal, which means
> that FPCR.IDC isn't set when it should be for FPCR.AH=1.
> We missed this when we added float_flag_input_denormal_used
> and made the fpu/ code set it.
> 
> Add the missing float_raise().
> 
> Cc:qemu-stable@nongnu.org
> Fixes: d38a57a3f ("target/arm: Enable FEAT_AFP for '-cpu max'")
> Signed-off-by: Peter Maydell<peter.maydell@linaro.org>
> ---
>   target/arm/tcg/sve_helper.c | 3 +++
>   1 file changed, 3 insertions(+)

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

r~

Peter Maydell <peter.maydell@linaro.org> writes:

> Our implementation of the FLOGB insn does the operations entirely
> in the helper function, without needing to use fpu functions.
> This means it needs to handle all the fp status flags itself.
> We aren't setting float_flag_input_denormal_used when we
> use (i.e. do not flush to zero) an input denormal, which means
> that FPCR.IDC isn't set when it should be for FPCR.AH=1.
> We missed this when we added float_flag_input_denormal_used
> and made the fpu/ code set it.
>
> Add the missing float_raise().
>
> Cc: qemu-stable@nongnu.org
> Fixes: d38a57a3f ("target/arm: Enable FEAT_AFP for '-cpu max'")
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro