[C PATCH, v2] Add Walloc-size to warn about insufficient size in allocations [PR71219]

[Martin Uecker via Gcc-patches]

Compared to the previous version I changed the name of the
warning to "Walloc-size" which matches "Wanalyzer-allocation-size"
but is still in line with the other -Walloc-something warnings
we have. I also added it to Wextra.

I found PR71219 that requests the warning and points out that 
it is recommended by the C secure coding guidelines and added
the PR to the commit log  (although the version with cast is not
diagnosed so far.)  

I did not have time to implement the extensions suggested
on the list,  i.e. warn when the size is not a multiple
of the size of the type and warn for if the size is not
suitable for a flexible array member. (this is also a bit
more complicated than it seems)

Bootstrapped and regression tested on x86_64.


Martin


Add option Walloc-size that warns about allocations that have
insufficient storage for the target type of the pointer the
storage is assigned to.

        PR c/71219
gcc:
        * doc/invoke.texi: Document -Walloc-size option.

gcc/c-family:

        * c.opt (Walloc-size): New option.

gcc/c:
        * c-typeck.cc (convert_for_assignment): Add warning.

gcc/testsuite:

        * gcc.dg/Walloc-size-1.c: New test.
---
 gcc/c-family/c.opt                   |  4 ++++
 gcc/c/c-typeck.cc                    | 27 +++++++++++++++++++++
 gcc/doc/invoke.texi                  | 10 ++++++++
 gcc/testsuite/gcc.dg/Walloc-size-1.c | 36 ++++++++++++++++++++++++++++
 4 files changed, 77 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/Walloc-size-1.c

diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
index 7348ad42ee0..9ba08a1fb6d 100644
--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -319,6 +319,10 @@ Walloca
 C ObjC C++ ObjC++ Var(warn_alloca) Warning
 Warn on any use of alloca.
 
+Walloc-size
+C ObjC Var(warn_alloc_size) Warning
+Warn when allocating insufficient storage for the target type of the assigned 
pointer.
+
 Walloc-size-larger-than=
 C ObjC C++ LTO ObjC++ Var(warn_alloc_size_limit) Joined Host_Wide_Int ByteSize 
Warning Init(HOST_WIDE_INT_MAX)
 -Walloc-size-larger-than=<bytes>       Warn for calls to allocation functions 
that
diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
index e2bfd2caf85..c759c6245ed 100644
--- a/gcc/c/c-typeck.cc
+++ b/gcc/c/c-typeck.cc
@@ -7384,6 +7384,33 @@ convert_for_assignment (location_t location, location_t 
expr_loc, tree type,
                    "request for implicit conversion "
                    "from %qT to %qT not permitted in C++", rhstype, type);
 
+      /* Warn of new allocations that are not big enough for the target
+        type.  */
+      tree fndecl;
+      if (warn_alloc_size
+         && TREE_CODE (rhs) == CALL_EXPR
+         && (fndecl = get_callee_fndecl (rhs)) != NULL_TREE
+         && DECL_IS_MALLOC (fndecl))
+       {
+         tree fntype = TREE_TYPE (fndecl);
+         tree fntypeattrs = TYPE_ATTRIBUTES (fntype);
+         tree alloc_size = lookup_attribute ("alloc_size", fntypeattrs);
+         if (alloc_size)
+           {
+             tree args = TREE_VALUE (alloc_size);
+             int idx = TREE_INT_CST_LOW (TREE_VALUE (args)) - 1;
+             /* For calloc only use the second argument.  */
+             if (TREE_CHAIN (args))
+               idx = TREE_INT_CST_LOW (TREE_VALUE (TREE_CHAIN (args))) - 1;
+             tree arg = CALL_EXPR_ARG (rhs, idx);
+             if (TREE_CODE (arg) == INTEGER_CST
+                 && tree_int_cst_lt (arg, TYPE_SIZE_UNIT (ttl)))
+                warning_at (location, OPT_Walloc_size, "allocation of "
+                            "insufficient size %qE for type %qT with "
+                            "size %qE", arg, ttl, TYPE_SIZE_UNIT (ttl));
+           }
+       }
+
       /* See if the pointers point to incompatible address spaces.  */
       asl = TYPE_ADDR_SPACE (ttl);
       asr = TYPE_ADDR_SPACE (ttr);
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 33befee7d6b..a4fbcf5e1b5 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -8086,6 +8086,16 @@ always leads to a call to another @code{cold} function 
such as wrappers of
 C++ @code{throw} or fatal error reporting functions leading to @code{abort}.
 @end table
 
+@opindex Wno-alloc-size
+@opindex Walloc-size
+@item -Walloc-size
+Warn about calls to allocation functions decorated with attribute
+@code{alloc_size} that specify insufficient size for the target type of
+the pointer the result is assigned to, including those to the built-in
+forms of the functions @code{aligned_alloc}, @code{alloca},
+@code{calloc},
+@code{malloc}, and @code{realloc}.
+
 @opindex Wno-alloc-zero
 @opindex Walloc-zero
 @item -Walloc-zero
diff --git a/gcc/testsuite/gcc.dg/Walloc-size-1.c 
b/gcc/testsuite/gcc.dg/Walloc-size-1.c
new file mode 100644
index 00000000000..61806f58192
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/Walloc-size-1.c
@@ -0,0 +1,36 @@
+/* Tests the warnings for insufficient allocation size.
+   { dg-do compile }
+   { dg-options "-Walloc-size" }
+ * */
+#include <stdlib.h>
+#include <alloca.h>
+
+struct b { int x[10]; };
+
+void fo0(void)
+{
+        struct b *p = malloc(sizeof *p);
+}
+
+void fo1(void)
+{
+        struct b *p = malloc(sizeof p);                /* { dg-warning 
"allocation of insufficient size" } */
+}
+
+void fo2(void)
+{
+        struct b *p = alloca(sizeof p);                /* { dg-warning 
"allocation of insufficient size" } */
+}
+
+void fo3(void)
+{
+        struct b *p = calloc(1, sizeof p);     /* { dg-warning "allocation of 
insufficient size" } */
+}
+
+void g(struct b* p);
+
+void fo4(void)
+{
+        g(malloc(4));                          /* { dg-warning "allocation of 
insufficient size" } */
+}
+
-- 
2.30.2