Re: [PATCH 1/4] target/ppc: initialize 'reg_val' in kvm_get_one_spr()

[Daniel Henrique Barboza <danielhb413@gmail.com>]

On 3/30/22 18:22, Philippe Mathieu-Daudé wrote:
> On 30/3/22 23:04, Daniel Henrique Barboza wrote:
>> Valgrind isn't convinced that we are initializing the values we assign
>> to env->spr[spr] because it doesn't understand that the 'reg_val' union
>> is being written by the kvm_vcpu_ioctl() that follows (via struct
>> kvm_one_reg).
>>
>> This results in Valgrind complaining about uninitialized values every
>> time we use env->spr in a conditional, like this instance:
>>
>> ==707578== Thread 1:
>> ==707578== Conditional jump or move depends on uninitialised value(s)
>> ==707578==    at 0xA10A40: hreg_compute_hflags_value (helper_regs.c:106)
>> ==707578==    by 0xA10C9F: hreg_compute_hflags (helper_regs.c:173)
>> ==707578==    by 0xA110F7: hreg_store_msr (helper_regs.c:262)
>> ==707578==    by 0xA051A3: ppc_cpu_reset (cpu_init.c:7168)
>> ==707578==    by 0xD4730F: device_transitional_reset (qdev.c:799)
>> ==707578==    by 0xD4A11B: resettable_phase_hold (resettable.c:182)
>> ==707578==    by 0xD49A77: resettable_assert_reset (resettable.c:60)
>> ==707578==    by 0xD4994B: resettable_reset (resettable.c:45)
>> ==707578==    by 0xD458BB: device_cold_reset (qdev.c:296)
>> ==707578==    by 0x48FBC7: cpu_reset (cpu-common.c:114)
>> ==707578==    by 0x97B5EB: spapr_reset_vcpu (spapr_cpu_core.c:38)
>> ==707578==    by 0x97BABB: spapr_cpu_core_reset (spapr_cpu_core.c:209)
>> ==707578==  Uninitialised value was created by a stack allocation
>> ==707578==    at 0xB11F08: kvm_get_one_spr (kvm.c:543)
>>
>> Initializing 'reg_val' has no impact in the logic and makes Valgrind
>> output more bearable.
>>
>> Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
>> ---
>>   target/ppc/kvm.c | 6 ++++--
>>   1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
>> index dc93b99189..ce1b926e8c 100644
>> --- a/target/ppc/kvm.c
>> +++ b/target/ppc/kvm.c
>> @@ -543,10 +543,12 @@ static void kvm_get_one_spr(CPUState *cs, uint64_t id, int spr)
>>   {
>>       PowerPCCPU *cpu = POWERPC_CPU(cs);
>>       CPUPPCState *env = &cpu->env;
>> -    union {
>> +    union reg_val {
>>           uint32_t u32;
>>           uint64_t u64;
>> -    } val;
>> +    };
>> +    /* Init reg_val to avoid "uninitialised value" Valgrind warnings */
>> +    union reg_val val = {0};
> 
> This should also work:
> 
> -- >8 --
> @@ -546,7 +546,7 @@ static void kvm_get_one_spr(CPUState *cs, uint64_t id, int spr)
>       union {
>           uint32_t u32;
>           uint64_t u64;
> -    } val;
> +    } val = { 0 };

Apparently it does work. I'll make a few tests and re-send.


Also, do we have an official way of spelling this zeroed struct initialization? I
see several instances of {0} and { 0 } in the code. In this series I used {0}.
./scripts/checkpatch.pl seems ok with both formats.


Thanks,


Daniel


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