Re: [XEN RFC PATCH 01/40] tools: Fix -Werror=maybe-uninitialized for xlu_pci_parse_bdf

[Jan Beulich <jbeulich@xxxxxxxx>]

On 11.08.2021 12:23, Wei Chen wrote:
> | libxlu_pci.c: In function 'xlu_pci_parse_bdf':
> | libxlu_pci.c:32:18: error: 'func' may be used uninitialized in this 
> function [-Werror=maybe-uninitialized]
> |    32 |     pcidev->func = func;
> |       |     ~~~~~~~~~~~~~^~~~~~

I'm afraid I can't spot such an assignment in the file (nor the two
similar ones further down). All I can see is 

    pci->domain = domain;
    pci->bus = bus;
    pci->dev = dev;
    pci->func = func;

> | libxlu_pci.c:51:29: note: 'func' was declared here
> |    51 |     unsigned dom, bus, dev, func, vslot = 0;
> |       |                             ^~~~
> | libxlu_pci.c:31:17: error: 'dev' may be used uninitialized in this function 
> [-Werror=maybe-uninitialized]
> |    31 |     pcidev->dev = dev;
> |       |     ~~~~~~~~~~~~^~~~~
> | libxlu_pci.c:51:24: note: 'dev' was declared here
> |    51 |     unsigned dom, bus, dev, func, vslot = 0;
> |       |                        ^~~
> | libxlu_pci.c:30:17: error: 'bus' may be used uninitialized in this function 
> [-Werror=maybe-uninitialized]
> |    30 |     pcidev->bus = bus;
> |       |     ~~~~~~~~~~~~^~~~~
> | libxlu_pci.c:51:19: note: 'bus' was declared here
> |    51 |     unsigned dom, bus, dev, func, vslot = 0;
> |       |                   ^~~
> | libxlu_pci.c:78:26: error: 'dom' may be used uninitialized in this function 
> [-Werror=maybe-uninitialized]
> |    78 |                 if ( dom & ~0xff )
> |       |                      ~~~~^~~~~~~

I'm afraid I also can't spot a variable named "dom", nor a sufficiently
similar if(). May I ask what code base these were observed with? Is the
change needed at all anymore?

> --- a/tools/libs/util/libxlu_pci.c
> +++ b/tools/libs/util/libxlu_pci.c
> @@ -15,7 +15,7 @@ static int parse_bdf(libxl_device_pci *pci, const char 
> *str, const char **endp)
>  {
>      const char *ptr = str;
>      unsigned int colons = 0;
> -    unsigned int domain, bus, dev, func;
> +    unsigned int domain = 0, bus = 0, dev = 0, func = 0;
>      int n;
>  
>      /* Count occurrences of ':' to detrmine presence/absence of the 'domain' 
> */
> @@ -28,7 +28,6 @@ static int parse_bdf(libxl_device_pci *pci, const char 
> *str, const char **endp)
>      ptr = str;
>      switch (colons) {
>      case 1:
> -        domain = 0;
>          if (sscanf(ptr, "%x:%x.%n", &bus, &dev, &n) != 2)
>              return ERROR_INVAL;
>          break;
> 

Also - which compiler did you encounter this with?

Finally please don't forget to Cc maintainers.

Jan