softfloat: Set 2-NaN propagation rule in float_status, not at compile time

[PATCH 10/21] target/m68k: Initialize float_status fields in gdb set/get functions

Posted by Peter Maydell 4 weeks, 1 day ago

In cf_fpu_gdb_get_reg() and cf_fpu_gdb_set_reg() we use a temporary
float_status variable to pass to floatx80_to_float64() and
float64_to_floatx80(), but we don't initialize it, meaning that those
functions could access uninitialized data.  Zero-init the structs.

(We don't need to set a NaN-propagation rule here because we
don't use these with a 2-argument fpu operation.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
Spotted by code-inspection while I was doing the 2-NaN propagation
patches.
---
 target/m68k/helper.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/target/m68k/helper.c b/target/m68k/helper.c
index 9d3db8419de..9bfc6ae97c0 100644
--- a/target/m68k/helper.c
+++ b/target/m68k/helper.c
@@ -36,7 +36,7 @@ static int cf_fpu_gdb_get_reg(CPUState *cs, GByteArray *mem_buf, int n)
     CPUM68KState *env = &cpu->env;
 
     if (n < 8) {
-        float_status s;
+        float_status s = {};
         return gdb_get_reg64(mem_buf, floatx80_to_float64(env->fregs[n].d, &s));
     }
     switch (n) {
@@ -56,7 +56,7 @@ static int cf_fpu_gdb_set_reg(CPUState *cs, uint8_t *mem_buf, int n)
     CPUM68KState *env = &cpu->env;
 
     if (n < 8) {
-        float_status s;
+        float_status s = {};
         env->fregs[n].d = float64_to_floatx80(ldq_be_p(mem_buf), &s);
         return 8;
     }
-- 
2.34.1

Re: [PATCH 10/21] target/m68k: Initialize float_status fields in gdb set/get functions

Posted by Richard Henderson 3 weeks, 5 days ago

On 10/25/24 15:12, Peter Maydell wrote:
> In cf_fpu_gdb_get_reg() and cf_fpu_gdb_set_reg() we use a temporary
> float_status variable to pass to floatx80_to_float64() and
> float64_to_floatx80(), but we don't initialize it, meaning that those
> functions could access uninitialized data.  Zero-init the structs.
> 
> (We don't need to set a NaN-propagation rule here because we
> don't use these with a 2-argument fpu operation.)
> 
> Signed-off-by: Peter Maydell<peter.maydell@linaro.org>
> ---
> Spotted by code-inspection while I was doing the 2-NaN propagation
> patches.
> ---
>   target/m68k/helper.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)

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

r~

Re: [PATCH 10/21] target/m68k: Initialize float_status fields in gdb set/get functions

Posted by Philippe Mathieu-Daudé 4 weeks ago

On 25/10/24 11:12, Peter Maydell wrote:
> In cf_fpu_gdb_get_reg() and cf_fpu_gdb_set_reg() we use a temporary
> float_status variable to pass to floatx80_to_float64() and
> float64_to_floatx80(), but we don't initialize it, meaning that those
> functions could access uninitialized data.  Zero-init the structs.
> 
> (We don't need to set a NaN-propagation rule here because we
> don't use these with a 2-argument fpu operation.)
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> Spotted by code-inspection while I was doing the 2-NaN propagation
> patches.
> ---
>   target/m68k/helper.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/target/m68k/helper.c b/target/m68k/helper.c
> index 9d3db8419de..9bfc6ae97c0 100644
> --- a/target/m68k/helper.c
> +++ b/target/m68k/helper.c
> @@ -36,7 +36,7 @@ static int cf_fpu_gdb_get_reg(CPUState *cs, GByteArray *mem_buf, int n)
>       CPUM68KState *env = &cpu->env;
>   
>       if (n < 8) {
> -        float_status s;
> +        float_status s = {};
>           return gdb_get_reg64(mem_buf, floatx80_to_float64(env->fregs[n].d, &s));

While here, could be renamed as 'discard' like SPARC. Regardless:

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

>       }
>       switch (n) {
> @@ -56,7 +56,7 @@ static int cf_fpu_gdb_set_reg(CPUState *cs, uint8_t *mem_buf, int n)
>       CPUM68KState *env = &cpu->env;
>   
>       if (n < 8) {
> -        float_status s;
> +        float_status s = {};
>           env->fregs[n].d = float64_to_floatx80(ldq_be_p(mem_buf), &s);
>           return 8;
>       }