objtool: Drop noinstr hack for KCSAN_WEAK_MEMORY

Now that the minimum supported version of LLVM for building the kernel
has been bumped to 15.0.0, __no_kcsan will always ensure that the thread
sanitizer functions are not generated, so remove the check for tsan
functions in is_profiling_func() and the always true depends and
unnecessary select lines in KCSAN_WEAK_MEMORY.

Acked-by: Marco Elver <elver@google.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infraded.org>
Reviewed-by: Kees Cook <kees@kernel.org>
Link: https://lore.kernel.org/r/20250821-bump-min-llvm-ver-15-v2-11-635f3294e5f0@kernel.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Author: nathanchance

lib/Kconfig.kcsan

@@ -185,12 +185,6 @@ config KCSAN_WEAK_MEMORY
 	bool "Enable weak memory modeling to detect missing memory barriers"
 	default y
 	depends on KCSAN_STRICT
-	# We can either let objtool nop __tsan_func_{entry,exit}() and builtin
-	# atomics instrumentation in .noinstr.text, or use a compiler that can
-	# implement __no_kcsan to really remove all instrumentation.
-	depends on !ARCH_WANTS_NO_INSTR || HAVE_NOINSTR_HACK || \
-		   CC_IS_GCC || CLANG_VERSION >= 140000
-	select OBJTOOL if HAVE_NOINSTR_HACK
 	help
 	  Enable support for modeling a subset of weak memory, which allows
 	  detecting a subset of data races due to missing memory barriers.

tools/objtool/check.c

@@ -2453,16 +2453,6 @@ static bool is_profiling_func(const char *name)
 	if (!strncmp(name, "__sanitizer_cov_", 16))
 		return true;
 
-	/*
-	 * Some compilers currently do not remove __tsan_func_entry/exit nor
-	 * __tsan_atomic_signal_fence (used for barrier instrumentation) with
-	 * the __no_sanitize_thread attribute, remove them. Once the kernel's
-	 * minimum Clang version is 14.0, this can be removed.
-	 */
-	if (!strncmp(name, "__tsan_func_", 12) ||
-	    !strcmp(name, "__tsan_atomic_signal_fence"))
-		return true;
-
 	return false;
 }