896026 - DOMStorageDBThread.cpp:859:9: warning: variable 'usage' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]

Status: RESOLVED DUPLICATE of bug 886184

(Core :: DOM: Core & HTML, defect)

Description

[Daniel Holbert [:dholbert]]

Clang gives me this build warning:
{
/mozilla-central/dom/src/storage/DOMStorageDBThread.cpp:859:9: warning: variable
      'usage' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
    if (exists) {
        ^~~~~~
/mozilla-central/dom/src/storage/DOMStorageDBThread.cpp:864:23: note: uninitialized
      use occurs here
    mUsage->LoadUsage(usage);
                      ^~~~~
/mozilla-central/dom/src/storage/DOMStorageDBThread.cpp:859:5: note: remove the 'if'
      if its condition is always true
    if (exists) {
    ^~~~~~~~~~~~
/mozilla-central/dom/src/storage/DOMStorageDBThread.cpp:858:18: note: initialize the
      variable 'usage' to silence this warning
    int64_t usage;
                 ^
                  = 0
}

The code in question is:
> 854     bool exists;
> 855     rv = stmt->ExecuteStep(&exists);
[...]
> 858     int64_t usage;
> 859     if (exists) {
> 860       rv = stmt->GetInt64(0, &usage);
> 861       NS_ENSURE_SUCCESS(rv, rv);
> 862     }
> 863 
> 864     mUsage->LoadUsage(usage);
> 865     break;

Indeed, if 'exists' is false, then we pass a bogus uninitialized value to mUsage->LoadUsage... That seems bad.  mayhemer, do you know what we should be doing instead?


(If it matters, the clang build that's reporting this to me is version 3.3 (svn revision 176869), the one currently recommended for our ASAN builds.)

Comment 1

[Honza Bambas (:mayhemer)]

Similar to bug 886184:

-    int64_t usage;
+    int64_t usage = 0;

Comment 2

[Daniel Holbert [:dholbert]]

It's about the same line of code, actually. Looks like bug 896026 just needs checking in.