Libunit: added macros that enhance type safety.

nxt_min()
nxt_max()
    Return the minimum/maximum of two values.

nxt_swap()
    Swap the values of two variables passed by their addresses.

nxt_sizeof_array()
    Return the size (in bytes) of an array.

nxt_nitems()
    Return the number of elements in an array.

nxt_memberof()
    Expand to a member of a structure.  It uses a compound literal for
    the object.

nxt_sizeof_incomplete()
    Calculate the size of an incomplete type, as if sizeof() could be
    applied to it.

nxt_sizeof_fam0()
    Calculate the size of each element of a FAM of a structure.

nxt_sizeof_fam()
    Calculate the size of a FAM of a structure.

nxt_offsetof_fam()
    Calculate the offset of the nth element of the FAM from the start of
    the containing structure.

nxt_sizeof_struct()
    Calculate the total size of a structure containing a FAM.  This
    value is the one that should be used for allocating the structure.

    Suggested-by: Andrew Clayton <a.clayton@nginx.com>

nxt_is_near_end()
    Evaluate to true if the member is near the end of a structure.  This
    is only designed to be used with FAMs, to make sure that the FAM is
    near the end of the structure (a zero-length array near the end of
    the structure would still pass this test, but it's a reasonable
    assertion to do.

    Suggested-by: David Laight <David.Laight@ACULAB.COM>

nxt_is_zero_sizeof()
    Evaluate to true if the size of 'x' is 0.

nxt_is_same_type()
    Evaluate to true if the both arguments are compatible types.

nxt_is_same_typeof()
    Evaluate to true if the types of both arguments are compatible.

nxt_is_array()
    Evaluate to true if the argument is an array.

nxt_must_be()
    It's like static_assert(3), but implemented as an expression.  It's
    necessary for writing the must_be_array() macro.  It's always
    evaluates to (int) 0.

nxt_must_be_array()
    Statically assert that the argument is an array.  It is an
    expression that always evaluates to (int) 0.

nxt_must_be_zero_sizeof()
    Statically assert that the argument has a size of 0.

nxt_must_be_near_end()
    Statically assert that a member of a structure is near the end of
    it.

    Suggested-by: David Laight <David.Laight@ACULAB.COM>

nxt_must_be_fam()
    Statically assert that the argument is a flexible array member
    (FAM).  It's an expression that always evaluates to (int) 0.

Link: <https://gustedt.wordpress.com/2011/03/14/flexible-array-member/>
Link: <https://lore.kernel.org/lkml/202308161913.91369D4A@keescook/T/>
Link: <https://inbox.sourceware.org/gcc/dac8afb7-5026-c702-85d2-c3ad977d9a48@kernel.org/T/>
Link: <https://stackoverflow.com/a/57537491>
Link: <https://github.com/shadow-maint/shadow/pull/762>
Cc: Andrew Clayton <a.clayton@nginx.com>
Cc: Zhidao Hong <z.hong@f5.com>
Signed-off-by: Alejandro Colomar <alx@nginx.com>
Signed-off-by: Alejandro Colomar <alx@kernel.org>

3 files changed, 92 insertions, 13 deletions

diff --git a/src/nxt_clang.h b/src/nxt_clang.h
index 94638346..10ed6687 100644
--- a/src/nxt_clang.h
+++ b/src/nxt_clang.h
@@ -8,6 +8,9 @@
 #define _NXT_CLANG_H_INCLUDED_
 
 
+#include <nxt_unit_cdefs.h>
+
+
 #define nxt_inline     static inline __attribute__((always_inline))
 #define nxt_noinline   __attribute__((noinline))
 #define nxt_cdecl
@@ -210,24 +213,12 @@ nxt_popcount(unsigned int x)
     *(type *) ((u_char *) p + offset)
 
 
-#define nxt_nitems(x)                                                         \
-    (sizeof(x) / sizeof((x)[0]))
-
-
 /* GCC and Clang use __builtin_abs() instead of libc abs(). */
 
 #define nxt_abs(val)                                                          \
     abs(val)
 
 
-#define nxt_max(val1, val2)                                                   \
-    ((val1 < val2) ? (val2) : (val1))
-
-
-#define nxt_min(val1, val2)                                                   \
-    ((val1 > val2) ? (val2) : (val1))
-
-
 #define nxt_bswap32(val)                                                      \
     (   ((val)               >> 24)                                           \
      | (((val) & 0x00FF0000) >>  8)                                           \
@@ -252,7 +243,7 @@ nxt_popcount(unsigned int x)
 
 
 #define nxt_length(s)                                                         \
-    (sizeof(s) - 1)
+    (sizeof(s) - 1 + nxt_must_be_array(s))
 
 
 #endif /* _NXT_CLANG_H_INCLUDED_ */
diff --git a/src/nxt_unit.h b/src/nxt_unit.h
index 35f9fa55..97e0e9df 100644
--- a/src/nxt_unit.h
+++ b/src/nxt_unit.h
@@ -15,6 +15,7 @@
 #include "nxt_auto_config.h"
 #include "nxt_version.h"
 #include "nxt_unit_typedefs.h"
+#include <nxt_unit_cdefs.h>
 
 
 enum {
diff --git a/src/nxt_unit_cdefs.h b/src/nxt_unit_cdefs.h
new file mode 100644
index 00000000..48389117
--- /dev/null
+++ b/src/nxt_unit_cdefs.h
@@ -0,0 +1,87 @@
+/*
+ * Copyright (C) 2019-2023, Alejandro Colomar <alx@kernel.org>
+ * Copyright (C) NGINX, Inc.
+ */
+
+#ifndef _NXT_UNIT_CDEFS_H_INCLUDED_
+#define _NXT_UNIT_CDEFS_H_INCLUDED_
+
+
+#include <stddef.h>
+
+
+#define nxt_max(a, b)            (((a) > (b)) ? (a) : (b))
+#define nxt_min(a, b)            (((a) < (b)) ? (a) : (b))
+
+
+#define nxt_swap(ap, bp)                                                      \
+    do {                                                                      \
+        __auto_type   ap_ = (ap);                                             \
+        __auto_type   bp_ = (bp);                                             \
+        typeof(*ap_)  tmp_;                                                   \
+                                                                              \
+        _Static_assert(nxt_is_same_typeof(ap_, bp_), "");                     \
+                                                                              \
+        tmp_ = *ap_;                                                          \
+        *ap_ = *bp_;                                                          \
+        *bp_ = tmp_;                                                          \
+    } while (0)
+
+
+#define nxt_sizeof_array(a)      (sizeof(a) + nxt_must_be_array(a))
+#define nxt_nitems(a)            (nxt_sizeof_array(a) / sizeof((a)[0]))
+#define nxt_memberof(T, member)  ((T){}.member)
+
+#define nxt_sizeof_incomplete(x)                                              \
+    (                                                                         \
+        sizeof(                                                               \
+            struct {                                                          \
+                max_align_t  a;                                               \
+                typeof(x)    inc;                                             \
+            }                                                                 \
+        )                                                                     \
+        - sizeof(max_align_t)                                                 \
+    )
+
+#define nxt_sizeof_fam0(T, fam)                                               \
+    (sizeof(nxt_memberof(T, fam[0])) + nxt_must_be_fam(T, fam))
+
+#define nxt_sizeof_fam(T, fam, n)                                             \
+    (nxt_sizeof_fam0(T, fam) * (n))
+
+#define nxt_offsetof_fam(T, fam, n)                                           \
+    (offsetof(T, fam) + nxt_sizeof_fam(T, fam, n))
+
+#define nxt_sizeof_struct(T, fam, n)                                          \
+    nxt_max(sizeof(T), nxt_offsetof_fam(T, fam, n))
+
+
+#define nxt_is_near_end(T, m)     (offsetof(T, m) > (sizeof(T) - _Alignof(T)))
+#define nxt_is_zero_sizeof(z)     (nxt_sizeof_incomplete(z) == 0)
+#define nxt_is_same_type(a, b)    __builtin_types_compatible_p(a, b)
+#define nxt_is_same_typeof(a, b)  nxt_is_same_type(typeof(a), typeof(b))
+#define nxt_is_array(a)           (!nxt_is_same_typeof(a, &(a)[0]))
+
+
+#define nxt_must_be(e)                                                        \
+    (                                                                         \
+        0 * (int) sizeof(                                                     \
+            struct {                                                          \
+                _Static_assert(e, "");                                        \
+                int ISO_C_forbids_a_struct_with_no_members_;                  \
+            }                                                                 \
+        )                                                                     \
+    )
+
+
+#define nxt_must_be_array(a)        nxt_must_be(nxt_is_array(a))
+#define nxt_must_be_zero_sizeof(z)  nxt_must_be(nxt_is_zero_sizeof(z))
+#define nxt_must_be_near_end(T, m)  nxt_must_be(nxt_is_near_end(T, m))
+
+#define nxt_must_be_fam(T, fam)                                               \
+    (nxt_must_be_array(nxt_memberof(T, fam))                                  \
+     + nxt_must_be_zero_sizeof(nxt_memberof(T, fam))                          \
+     + nxt_must_be_near_end(T, fam))
+
+
+#endif /* _NXT_UNIT_CDEFS_H_INCLUDED_ */