[PATCH] vasnprintf: silence some clang false positives

[Eric Blake]

Clang does not realize that result can only ever be NULL when
allocated==0, or that (needed) is always positive so that the
true branch will always be taken when result starts life as
NULL.  Adding a false branch fixes the analysis, even though
the false branch will never be taken.

* lib/vasnprintf.c (VASNPRINTF) [ENSURE_ALLOCATION]: Teach clang
that ENSURE_ALLOCATION guarantees a non-null result.

Signed-off-by: Eric Blake <address@hidden>
---

Bruno, would you be okay with this patch?  clang correctly deduces
that when resultbuf==NULL at function entry, then result starts life
as NULL prior to the main loop.  However, it fails to realize that
result is only ever NULL when allocation is also 0, and therefore
assumes that the false branch of ENSURE_ALLOCATION can be taken which
would leave result as NULL.  Without this patch, that results in
several false positive NULL-dereference warnings.

 ChangeLog        |    6 ++++++
 lib/vasnprintf.c |    4 +++-
 2 files changed, 9 insertions(+), 1 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 4693863..fc79f31 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2011-02-14  Eric Blake  <address@hidden>
+
+       vasnprintf: silence some clang false positives
+       * lib/vasnprintf.c (VASNPRINTF) [ENSURE_ALLOCATION]: Teach clang
+       that ENSURE_ALLOCATION guarantees a non-null result.
+
 2011-02-13  Bruno Haible  <address@hidden>

        mbrtowc: Add more tests for native Windows platforms.
diff --git a/lib/vasnprintf.c b/lib/vasnprintf.c
index 8f07308..ea6e5a2 100644
--- a/lib/vasnprintf.c
+++ b/lib/vasnprintf.c
@@ -1837,7 +1837,9 @@ VASNPRINTF (DCHAR_T *resultbuf, size_t *lengthp,
         if (result == resultbuf && length > 0)                               \
           DCHAR_CPY (memory, result, length);                                \
         result = memory;                                                     \
-      }
+      }                                                                      \
+    else if (!result)                                                        \
+      abort ()

     for (cp = format, i = 0, dp = &d.dir[0]; ; cp = dp->dir_end, i++, dp++)
       {
-- 
1.7.4