Re: [PATCH v2 1/4] target/ppc: initialize 'val' union in kvm_get_one_spr()

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, Mar 30, 2022 at 09:17:14PM -0300, 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 '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 'val' has no impact in the logic and makes Valgrind output
> more bearable.
> 
> Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
>  target/ppc/kvm.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
> index dc93b99189..858866ecd4 100644
> --- a/target/ppc/kvm.c
> +++ b/target/ppc/kvm.c
> @@ -543,10 +543,11 @@ static void kvm_get_one_spr(CPUState *cs, uint64_t id, int spr)
>  {
>      PowerPCCPU *cpu = POWERPC_CPU(cs);
>      CPUPPCState *env = &cpu->env;
> +    /* Init 'val' to avoid "uninitialised value" Valgrind warnings */
>      union {
>          uint32_t u32;
>          uint64_t u64;
> -    } val;
> +    } val = { };
>      struct kvm_one_reg reg = {
>          .id = id,
>          .addr = (uintptr_t) &val,

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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