lib/alloc.h: Reimplement [X]REALLOC[F]() macros with _Generic(3)

Instead of GNU builtins and extensions, these macros can be implemented
with C11's _Generic(3), and the result is much simpler (and safer, since
it's now an error, not just a warning).

Signed-off-by: Alejandro Colomar <alx@kernel.org>

diff --git a/lib/alloc.h b/lib/alloc.h
index 0e04884947cae5bbb5e1686bd1ed1f0acc34b2d0..39405a56fc1d7f602f2b4ba0685fd268f07aae96 100644 (file)
--- a/lib/alloc.h
+++ b/lib/alloc.h
@@ -1,8 +1,5 @@
-/*
- * SPDX-FileCopyrightText:  2023, Alejandro Colomar <alx@kernel.org>
- *
- * SPDX-License-Identifier:  BSD-3-Clause
- */
+// SPDX-FileCopyrightText: 2023-2024, Alejandro Colomar <alx@kernel.org>
+// SPDX-License-Identifier: BSD-3-Clause
 
 
 #ifndef SHADOW_INCLUDE_LIB_MALLOC_H_
@@ -27,31 +24,19 @@
 #define XMALLOC(n, type)  ((type *) xmallocarray(n, sizeof(type)))
 
 #define REALLOC(ptr, n, type)                                                 \
-({                                                                            \
-       __auto_type  p_ = (ptr);                                              \
-                                                                              \
-       static_assert(__builtin_types_compatible_p(typeof(p_), type *), "");  \
-                                                                              \
-       (type *) reallocarray(p_, n, sizeof(type));                           \
-})
+(                                                                             \
+       _Generic(ptr, type *:  (type *) reallocarray(ptr, n, sizeof(type)))   \
+)
 
 #define REALLOCF(ptr, n, type)                                                \
-({                                                                            \
-       __auto_type  p_ = (ptr);                                              \
-                                                                              \
-       static_assert(__builtin_types_compatible_p(typeof(p_), type *), "");  \
-                                                                              \
-       (type *) reallocarrayf(p_, n, sizeof(type));                          \
-})
+(                                                                             \
+       _Generic(ptr, type *:  (type *) reallocarrayf(ptr, n, sizeof(type)))  \
+)
 
 #define XREALLOC(ptr, n, type)                                                \
-({                                                                            \
-       __auto_type  p_ = (ptr);                                              \
-                                                                              \
-       static_assert(__builtin_types_compatible_p(typeof(p_), type *), "");  \
-                                                                              \
-       (type *) xreallocarray(p_, n, sizeof(type));                          \
-})
+(                                                                             \
+       _Generic(ptr, type *:  (type *) xreallocarray(ptr, n, sizeof(type)))  \
+)
 
 
 ATTR_MALLOC(free)