Re: [PATCH 3/6] target/ppc: Don't initialize some local variables in ppc_radix64_xlate()

[Cédric Le Goater]

On 5/7/20 7:26 PM, Greg Kurz wrote:
> It is the job of the ppc_radix64_get_fully_qualified_addr() function
> which is called at the beginning of ppc_radix64_xlate() to set both
> lpid *and* pid. It doesn't buy us anything to initialize them first.
> 
> Worse, a bug in ppc_radix64_get_fully_qualified_addr(), eg. failing to
> set either lpid or pid, would be undetectable by static analysis tools
> like coverity.
> 
> Signed-off-by: Greg Kurz <address@hidden>
> ---
>  target/ppc/mmu-radix64.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/target/ppc/mmu-radix64.c b/target/ppc/mmu-radix64.c
> index c76879f65b78..5e2d912ee346 100644
> --- a/target/ppc/mmu-radix64.c
> +++ b/target/ppc/mmu-radix64.c
> @@ -433,7 +433,7 @@ static int ppc_radix64_xlate(PowerPCCPU *cpu, vaddr 
> eaddr, int rwx,
>                               bool cause_excp)
>  {
>      CPUPPCState *env = &cpu->env;
> -    uint64_t lpid = 0, pid = 0;
> +    uint64_t lpid, pid;
>      ppc_v3_pate_t pate;
>      int psize, prot;
>      hwaddr g_raddr;
> 

I am seeing this failure with gcc version 9.3.1 20200408 (Red Hat 9.3.1-2) 
(GCC) 

target/ppc/mmu-radix64.c: In function ‘ppc_radix64_xlate’:
target/ppc/mmu-radix64.c:314:12: error: ‘pid’ may be used uninitialized in this 
function [-Werror=maybe-uninitialized]
  314 |     offset = pid * sizeof(struct prtb_entry);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
target/ppc/mmu-radix64.c:439:20: note: ‘pid’ was declared here
  439 |     uint64_t lpid, pid;
      |                    ^~~
target/ppc/mmu-radix64.c:458:14: error: ‘lpid’ may be used uninitialized in 
this function [-Werror=maybe-uninitialized]
  458 |         if (!ppc64_v3_get_pate(cpu, lpid, &pate)) {
      |              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  CC      ppc64-softmmu/target/ppc/fpu_helper.o


This seems like a compiler optimization issue.

C.