libxl: workaround gcc 10.2 maybe-uninitialized warning

It seems xlu_pci_parse_bdf has a state machine that is too complex for
gcc to understand. The build fails with:

    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;
          |     ~~~~~~~~~~~~~^~~~~~
    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:29:20: error: 'dom' may be used uninitialized in this function [-Werror=maybe-uninitialized]
       29 |     pcidev->domain = domain;
          |     ~~~~~~~~~~~~~~~^~~~~~~~
    libxlu_pci.c:51:14: note: 'dom' was declared here
       51 |     unsigned dom, bus, dev, func, vslot = 0;
          |              ^~~
    cc1: all warnings being treated as errors

Workaround it by setting the initial value to invalid value (0xffffffff)
and then assert on each value being set. This way we mute the gcc
warning, while still detecting bugs in the parse code.

Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Reviewed-by: Ian Jackson <ian.jackson@eu.citrix.com>

diff --git a/tools/libxl/libxlu_pci.c b/tools/libxl/libxlu_pci.c
index 7947687661cf2f6f8d68db23fb5d5415106c2e51..e2709c5f8957127b540aff650c38aadcc6660ad4 100644 (file)
--- a/tools/libxl/libxlu_pci.c
+++ b/tools/libxl/libxlu_pci.c
@@ -45,10 +45,11 @@ static int pcidev_struct_fill(libxl_device_pci *pcidev, unsigned int domain,
 #define STATE_TYPE      9
 #define STATE_RDM_STRATEGY      10
 #define STATE_RESERVE_POLICY    11
+#define INVALID         0xffffffff
 int xlu_pci_parse_bdf(XLU_Config *cfg, libxl_device_pci *pcidev, const char *str)
 {
     unsigned state = STATE_DOMAIN;
-    unsigned dom, bus, dev, func, vslot = 0;
+    unsigned dom = INVALID, bus = INVALID, dev = INVALID, func = INVALID, vslot = 0;
     char *buf2, *tok, *ptr, *end, *optkey = NULL;
 
     if ( NULL == (buf2 = ptr = strdup(str)) )
@@ -170,6 +171,8 @@ int xlu_pci_parse_bdf(XLU_Config *cfg, libxl_device_pci *pcidev, const char *str
     if ( tok != ptr || state != STATE_TERMINAL )
         goto parse_error;
 
+    assert(dom != INVALID && bus != INVALID && dev != INVALID && func != INVALID);
+
     /* Just a pretty way to fill in the values */
     pcidev_struct_fill(pcidev, dom, bus, dev, func, vslot << 3);