ANDROID: update KABI macros for gendwarfksyms

With the transition from genksyms to gendwarfksyms, the mechanisms for
achieving stable MODVERSIONS CRCs in the face of "safe" ABI changes are
now very different.

The macros for padding reservation / use have much the same interface,
though the variant specifically for vendors has been dropped as it was
barely used.

It is no longer possible to use compilation conditional on __GENKSYMS__
to control what is visible to symtypes generation as that now uses DWARF
information from a single compilation pass (as opposed to source from a
separate preprocessing pass).

There are specific macros to deal with common cases like member
replacement, enumerator addition and unwanted type definitions.

Note that there is as yet no support for dealing with type size changes.

Bug: 400972353
Change-Id: Ic9abadadeed6ca8f7be82165f831dab6f34e98d2
Signed-off-by: Giuliano Procida <gprocida@google.com>

Author: myxoid

include/linux/android_kabi.h

@@ -2,7 +2,7 @@
 /*
  * android_kabi.h - Android kernel abi abstraction header
  *
- * Copyright (C) 2020 Google, Inc.
+ * Copyright (C) 2020-2025 Google, Inc.
  *
  * Heavily influenced by rh_kabi.h which came from the RHEL/CENTOS kernel and
  * was:
@@ -29,49 +29,49 @@
  *    If a field is added to a structure, the padding fields can be used to add
  *    the new field in a "safe" way.
  */
+
 #ifndef _ANDROID_KABI_H
 #define _ANDROID_KABI_H
 
+#include <linux/args.h>
 #include <linux/compiler.h>
+#include <linux/compiler_attributes.h>
 #include <linux/stringify.h>
 
 /*
  * Worker macros, don't use these, use the ones without a leading '_'
  */
 
-#define __ANDROID_KABI_CHECK_SIZE_ALIGN(_orig, _new)				\
-	union {									\
-		_Static_assert(sizeof(struct{_new;}) <= sizeof(struct{_orig;}),	\
-			       __FILE__ ":" __stringify(__LINE__) ": "		\
-			       __stringify(_new)				\
-			       " is larger than "				\
-			       __stringify(_orig) );				\
-		_Static_assert(__alignof__(struct{_new;}) <= __alignof__(struct{_orig;}),	\
-			       __FILE__ ":" __stringify(__LINE__) ": "		\
-			       __stringify(_orig)				\
-			       " is not aligned the same as "			\
-			       __stringify(_new) );				\
+#define _ANDROID_KABI_RULE(hint, target, value)				 \
+	static const char CONCATENATE(__gendwarfksyms_rule_,		 \
+				      __COUNTER__)[] __used __aligned(1) \
+		__section(".discard.gendwarfksyms.kabi_rules") =	 \
+			"1\0" #hint "\0" #target "\0" #value
+
+#define _ANDROID_KABI_NORMAL_SIZE_ALIGN(_orig, _new)			\
+	union {								\
+		_Static_assert(						\
+			sizeof(struct { _new; }) <=			\
+				sizeof(struct { _orig; }),		\
+			FILE_LINE ": " __stringify(_new)		\
+				" is larger than " __stringify(_orig));	\
+		_Static_assert(						\
+			__alignof__(struct { _new; }) <=		\
+				__alignof__(struct { _orig; }),		\
+			FILE_LINE ": " __stringify(_orig)		\
+				" is not aligned the same as "		\
+				__stringify(_new));			\
 	}
 
-#ifdef __GENKSYMS__
-
-#define _ANDROID_KABI_REPLACE(_orig, _new)		_orig
-
-#else
-
-#define _ANDROID_KABI_REPLACE(_orig, _new)			\
-	union {							\
-		_new;						\
-		struct {					\
-			_orig;					\
-		};						\
-		__ANDROID_KABI_CHECK_SIZE_ALIGN(_orig, _new);	\
+#define _ANDROID_KABI_REPLACE(_orig, _new)		      \
+	union {						      \
+		_new;					      \
+		struct {				      \
+			_orig;				      \
+		};					      \
+		_ANDROID_KABI_NORMAL_SIZE_ALIGN(_orig, _new); \
 	}
 
-#endif /* __GENKSYMS__ */
-
-#define _ANDROID_KABI_RESERVE(n)		u64 __kabi_reserved##n
-
 
 /*
  * Macros to use _before_ the ABI is frozen
@@ -84,44 +84,61 @@
  *   number: the "number" of the padding variable in the structure.  Start with
  *   1 and go up.
  */
-#ifdef CONFIG_ANDROID_KABI_RESERVE
-#define ANDROID_KABI_RESERVE(number)	_ANDROID_KABI_RESERVE(number)
-#else
-#define ANDROID_KABI_RESERVE(number)
-#endif
+#define ANDROID_KABI_RESERVE(number)	u64 __kabi_reserved##number
 
 /*
- * ANDROID_KABI_BACKPORT_OK
- *   Used to allow padding originally reserved with ANDROID_KABI_RESERVE
- *   to be used for backports of non-LTS patches by partners. These
- *   fields can by used by replacing with ANDROID_KABI_BACKPORT_USE()
- *   for partner backports.
+ * Macros to use _after_ the ABI is frozen
  */
-#define ANDROID_KABI_BACKPORT_OK(number) ANDROID_KABI_RESERVE(number)
 
 /*
- * Macros to use _after_ the ABI is frozen
+ * ANDROID_KABI_DECLONLY(fqn)
+ *   Treat the struct/union/enum fqn as a declaration, i.e. even if
+ *   a definition is available, don't expand the contents.
+ */
+#define ANDROID_KABI_DECLONLY(fqn)	_ANDROID_KABI_RULE(declonly, fqn, /**/)
+
+/*
+ * ANDROID_KABI_ENUMERATOR_IGNORE(fqn, field)
+ *   When expanding enum fqn, skip the provided field. This makes it
+ *   possible to hide added enum fields from versioning.
+ */
+#define ANDROID_KABI_ENUMERATOR_IGNORE(fqn, field) \
+	_ANDROID_KABI_RULE(enumerator_ignore, fqn field, /**/)
+
+/*
+ * ANDROID_KABI_ENUMERATOR_VALUE(fqn, field, value)
+ *   When expanding enum fqn, use the provided value for the
+ *   specified field. This makes it possible to override enumerator
+ *   values when calculating versions.
+ */
+#define ANDROID_KABI_ENUMERATOR_VALUE(fqn, field, value) \
+	_ANDROID_KABI_RULE(enumerator_value, fqn field, value)
+
+/*
+ * ANDROID_KABI_IGNORE
+ *   Add a new field that's ignored in versioning.
+ */
+#define ANDROID_KABI_IGNORE(n, _new)		 \
+	union {					 \
+		_new;				 \
+		unsigned char __kabi_ignored##n; \
+	}
+
+/*
+ * ANDROID_KABI_REPLACE
+ *   Replace a field with a compatible new field.
  */
+#define ANDROID_KABI_REPLACE(_oldtype, _oldname, _new) \
+	_ANDROID_KABI_REPLACE(_oldtype __kabi_renamed##_oldname, struct { _new; })
 
 /*
  * ANDROID_KABI_USE(number, _new)
  *   Use a previous padding entry that was defined with ANDROID_KABI_RESERVE
  *   number: the previous "number" of the padding variable
  *   _new: the variable to use now instead of the padding variable
  */
-#define ANDROID_KABI_USE(number, _new)		\
-	_ANDROID_KABI_REPLACE(_ANDROID_KABI_RESERVE(number), _new)
-
-/*
- * ANDROID_KABI_BACKPORT_USE(number, _new)
- *   Use a previous padding entry that was defined with
- *   ANDROID_KABI_BACKPORT_OK(). This is functionally identical
- *   to ANDROID_KABI_USE() except that it differentiates the
- *   normal use of KABI fields for LTS from KABI fields that
- *   were released for use with other backports from upstream.
- */
-#define ANDROID_KABI_BACKPORT_USE(number, _new) \
-	ANDROID_KABI_USE(number, _new)
+#define ANDROID_KABI_USE(number, _new) \
+	_ANDROID_KABI_REPLACE(ANDROID_KABI_RESERVE(number), _new)
 
 /*
  * ANDROID_KABI_USE2(number, _new1, _new2)
@@ -130,8 +147,8 @@
  *   want to "burn" a 64bit padding variable for a smaller variable size if not
  *   needed.
  */
-#define ANDROID_KABI_USE2(number, _new1, _new2)			\
-	_ANDROID_KABI_REPLACE(_ANDROID_KABI_RESERVE(number), struct{ _new1; _new2; })
+#define ANDROID_KABI_USE2(number, _new1, _new2) \
+	_ANDROID_KABI_REPLACE(ANDROID_KABI_RESERVE(number), struct{ _new1; _new2; })
 
 
 #endif /* _ANDROID_KABI_H */