[Qemu-devel] [PATCH RFC] coverity: Improve model for GLib memory allocation

[Markus Armbruster]

In current versions of GLib, g_new() may expand into g_malloc_n(),
which we don't model.  When it does, Coverity can't see the memory
allocation.  Similarly for g_new0(), g_renew(), g_try_new(),
g_try_new0(), g_try_renew().

Model g_try_malloc_n(), g_malloc_n(), g_try_malloc0_n(),
g_malloc0_n(), g_try_realloc_n().  To avoid undue duplication, rewrite
the existing memory allocation models on top of them.

In my local testing, this gets rid of false positives.  But it also
adds a few, and has a few other effects I can't explain.  Posting as
RFC, will follow up with details.

Signed-off-by: Markus Armbruster <address@hidden>
---
 scripts/coverity-model.c | 80 ++++++++++++++++++++++++++++++------------------
 1 file changed, 50 insertions(+), 30 deletions(-)

diff --git a/scripts/coverity-model.c b/scripts/coverity-model.c
index 4c99a85..4e5508a 100644
--- a/scripts/coverity-model.c
+++ b/scripts/coverity-model.c
@@ -112,55 +112,75 @@ void *calloc(size_t, size_t);
 void *realloc(void *, size_t);
 void free(void *);
 
-void *
-g_malloc(size_t n_bytes)
+void *g_try_malloc_n(size_t nmemb, size_t size)
 {
-    void *mem;
-    __coverity_negative_sink__(n_bytes);
-    mem = malloc(n_bytes == 0 ? 1 : n_bytes);
-    if (!mem) __coverity_panic__();
-    return mem;
+    size_t sz;
+
+    __coverity_negative_sink__(nmemb);
+    __coverity_negative_sink__(size);
+    sz = nmemb * size;
+    return malloc(sz == 0 ? 1 : sz);
 }
 
-void *
-g_malloc0(size_t n_bytes)
+void *g_malloc_n(size_t nmemb, size_t size)
 {
-    void *mem;
-    __coverity_negative_sink__(n_bytes);
-    mem = calloc(1, n_bytes == 0 ? 1 : n_bytes);
-    if (!mem) __coverity_panic__();
-    return mem;
+    void *ptr = g_try_malloc_n(nmemb, size);
+
+    if (!ptr) __coverity_panic__();
+    return ptr;
 }
 
-void g_free(void *mem)
+void *g_try_malloc0_n(size_t nmemb, size_t size)
 {
-    free(mem);
+    if (nmemb == 0 || size == 0) {
+        return malloc(1);
+    }
+    return calloc(nmemb, size);
 }
 
-void *g_realloc(void * mem, size_t n_bytes)
+void *g_malloc0_n(size_t nmemb, size_t size)
 {
-    __coverity_negative_sink__(n_bytes);
-    mem = realloc(mem, n_bytes == 0 ? 1 : n_bytes);
-    if (!mem) __coverity_panic__();
-    return mem;
+    void *ptr = g_try_malloc0_n(nmemb, size);
+
+    if (!ptr) __coverity_panic__();
+    return ptr;
+}
+
+void *g_malloc(size_t size)
+{
+    return g_malloc_n(1, size);
+}
+
+void *g_malloc0(size_t size)
+{
+    return g_malloc0_n(1, size);
+}
+
+void *g_try_realloc_n(void *ptr, size_t nmemb, size_t size)
+{
+    size_t sz;
+
+    __coverity_negative_sink__(nmemb);
+    __coverity_negative_sink__(size);
+    sz = nmemb * size;
+    return realloc(ptr, sz == 0 ? 1 : sz);
 }
 
-void *g_try_malloc(size_t n_bytes)
+void *g_try_realloc(void *ptr, size_t size)
 {
-    __coverity_negative_sink__(n_bytes);
-    return malloc(n_bytes == 0 ? 1 : n_bytes);
+    return g_try_realloc_n(ptr, 1, size);
 }
 
-void *g_try_malloc0(size_t n_bytes)
+void *g_realloc(void *ptr, size_t size)
 {
-    __coverity_negative_sink__(n_bytes);
-    return calloc(1, n_bytes == 0 ? 1 : n_bytes);
+    ptr = g_try_realloc(ptr, size);
+    if (!ptr) __coverity_panic__();
+    return ptr;
 }
 
-void *g_try_realloc(void *mem, size_t n_bytes)
+void g_free(void *ptr)
 {
-    __coverity_negative_sink__(n_bytes);
-    return realloc(mem, n_bytes == 0 ? 1 : n_bytes);
+    free(ptr);
 }
 
 /* Other glib functions */
-- 
1.9.3