compiler.h: unify __UNIQUE_ID

commit 6f33d587 ("__UNIQUE_ID()")
added a fallback definition of __UNIQUE_ID because gcc 4.2 and older did
not support __COUNTER__.

Also, this commit is effectively a revert of
commit b41c29b0 ("Kbuild: provide a __UNIQUE_ID for clang")
which mentions clang 2.6+ supporting __COUNTER__.

Documentation/process/changes.rst currently lists the minimum supported
version of these compilers as:
- gcc: 5.1
- clang: 11.0.0
It should be safe to say that __COUNTER__ is well supported by this
point.

Link: https://lkml.kernel.org/r/20230831-unique_id-v1-1-28bacd18eb1d@google.comSigned-off-by: Nick Desaulniers <ndesaulniers@google.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Jan Beulich <jbeulich@suse.com>
Cc: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Cc: Michal rarek <mmarek@suse.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Paul Russel <rusty@rustcorp.com.au>
Cc: Tom Rix <trix@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/compiler-clang.h

@@ -14,11 +14,6 @@
 #undef __cleanup
 #define __cleanup(func) __maybe_unused __attribute__((__cleanup__(func)))
 
-/* same as gcc, this was present in clang-2.6 so we can assume it works
- * with any version that can compile the kernel
- */
-#define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)
-
 /* all clang versions usable with the kernel support KASAN ABI version 5 */
 #define KASAN_ABI_VERSION 5
 

include/linux/compiler-gcc.h

@@ -39,8 +39,6 @@
 #define __noretpoline __attribute__((__indirect_branch__("keep")))
 #endif
 
-#define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)
-
 #if defined(LATENT_ENTROPY_PLUGIN) && !defined(__CHECKER__)
 #define __latent_entropy __attribute__((latent_entropy))
 #endif

include/linux/compiler.h

@@ -177,10 +177,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 	__asm__ ("" : "=r" (var) : "0" (var))
 #endif
 
-/* Not-quite-unique ID. */
-#ifndef __UNIQUE_ID
-# define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __LINE__)
-#endif
+#define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)
 
 /**
  * data_race - mark an expression as containing intentional data races