Re: [PATCH v2 2/4] target/ppc: init 'lpcr' in kvmppc_enable_cap_large_decr()

[David Gibson]

On Wed, Mar 30, 2022 at 09:17:15PM -0300, Daniel Henrique Barboza wrote:
> 'lpcr' is used as an input of kvm_get_one_reg(). Valgrind doesn't
> understand that and it returns warnings as such for this function:
> 
> ==55240== Thread 1:
> ==55240== Conditional jump or move depends on uninitialised value(s)
> ==55240==    at 0xB011E4: kvmppc_enable_cap_large_decr (kvm.c:2546)
> ==55240==    by 0x92F28F: cap_large_decr_cpu_apply (spapr_caps.c:523)
> ==55240==    by 0x930C37: spapr_caps_cpu_apply (spapr_caps.c:921)
> ==55240==    by 0x955D3B: spapr_reset_vcpu (spapr_cpu_core.c:73)
> ==55240==    by 0x95612B: spapr_cpu_core_reset (spapr_cpu_core.c:209)
> ==55240==    by 0x95619B: spapr_cpu_core_reset_handler (spapr_cpu_core.c:218)
> ==55240==    by 0xD3605F: qemu_devices_reset (reset.c:69)
> ==55240==    by 0x92112B: spapr_machine_reset (spapr.c:1641)
> ==55240==    by 0x4FBD63: qemu_system_reset (runstate.c:444)
> ==55240==    by 0x62812B: qdev_machine_creation_done (machine.c:1247)
> ==55240==    by 0x5064C3: qemu_machine_creation_done (vl.c:2725)
> ==55240==    by 0x5065DF: qmp_x_exit_preconfig (vl.c:2748)
> ==55240==  Uninitialised value was created by a stack allocation
> ==55240==    at 0xB01158: kvmppc_enable_cap_large_decr (kvm.c:2540)
> 
> Init 'lpcr' to avoid this warning.

Hmm... this is seeming a bit like whack-a-mole.  Could we instead use
one of the valgrind hinting mechanisms to inform it that
kvm_get_one_reg() writes the variable at *target?

> Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
> ---
>  target/ppc/kvm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
> index 858866ecd4..42814e1b97 100644
> --- a/target/ppc/kvm.c
> +++ b/target/ppc/kvm.c
> @@ -2538,7 +2538,7 @@ int kvmppc_get_cap_large_decr(void)
>  int kvmppc_enable_cap_large_decr(PowerPCCPU *cpu, int enable)
>  {
>      CPUState *cs = CPU(cpu);
> -    uint64_t lpcr;
> +    uint64_t lpcr = 0;
>  
>      kvm_get_one_reg(cs, KVM_REG_PPC_LPCR_64, &lpcr);
>      /* Do we need to modify the LPCR? */

-- 
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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