[xen staging] libxl: workaround gcc 10.2 maybe-uninitialized warning

[patchbot@xxxxxxx]

commit d25cc3ec93ebda030349045d2c7fa14ffde07ed7
Author:     Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
AuthorDate: Wed Aug 19 04:00:35 2020 +0200
Commit:     Wei Liu <wl@xxxxxxx>
CommitDate: Thu Aug 27 09:36:39 2020 +0000

    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@xxxxxxxxxxxxxxxxxxxxxx>
    Reviewed-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
---
 tools/libxl/libxlu_pci.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tools/libxl/libxlu_pci.c b/tools/libxl/libxlu_pci.c
index 7947687661..e2709c5f89 100644
--- 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);
 
--
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