[PATCH v4 18/21] compiler.h: RFC - s/__LINE__/__COUNTER__/ in __UNIQUE_ID fallback

[Jim Cromie]

We currently have 3 defns for __UNIQUE_ID(); gcc and clang are using
__COUNTER__ for real uniqueness, 3rd just uses __LINE__, which should
fail on this (and harder to avoid situations):

  DECLARE_FOO(); DECLARE_FOO();

Its 2023, can we haz a no-fallback __UNIQUE_ID ?

NOTE:

This also changes __UNIQUE_ID_ to _kaUID_.  Ive been getting
lkp-reports of collisions on names which should be unique; this
shouldnt happen on gcc & clang, but does on some older ones, on some
platforms, on some allyes & rand-configs.  Like this:

mips64-linux-ld:
drivers/gpu/drm/display/drm_dp_helper.o:(__dyndbg_class_users+0x0):
multiple definition of `__UNIQUE_ID_ddebug_class_user405';
drivers/gpu/drm/drm_gem_shmem_helper.o:(__dyndbg_class_users+0x0):
first defined here

Like above, the collision reports appear to always be 3-digit
counters, which look like line-numbers.  Changing to _kaUID_ in this
defn should make it more obvious (in *.i file) when a fallback has
happened.  To be clear, I havent seen it yet.  Nor have I seen the
multiple-defn problem above since adding this patch.

Lets see what lkp-robot says about this.

CC: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx> (maintainer:SPARSE CHECKER)
CC: Nathan Chancellor <nathan@xxxxxxxxxx> (supporter:CLANG/LLVM BUILD SUPPORT)
CC: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> (supporter:CLANG/LLVM BUILD SUPPORT)
CC: Tom Rix <trix@xxxxxxxxxx> (reviewer:CLANG/LLVM BUILD SUPPORT)
CC: linux-sparse@xxxxxxxxxxxxxxx (open list:SPARSE CHECKER)
CC: linux-kernel@xxxxxxxxxxxxxxx (open list)
CC: llvm@xxxxxxxxxxxxxxx (open list:CLANG/LLVM BUILD SUPPORT)
Signed-off-by: Jim Cromie <jim.cromie@xxxxxxxxx>
---
 include/linux/compiler.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index d7779a18b24f..677d6c47cd9e 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -177,9 +177,9 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 	__asm__ ("" : "=r" (var) : "0" (var))
 #endif
 
-/* Not-quite-unique ID. */
+/* JFTI: to fix Not-quite-unique ID */
 #ifndef __UNIQUE_ID
-# define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __LINE__)
+# define __UNIQUE_ID(prefix) __PASTE(__PASTE(_kaUID_, prefix), __COUNTER__)
 #endif
 
 /**
-- 
2.41.0