[PATCH 2/3] kconfig: Replace "cc-option-bit" with "cc-option-str"

[Kees Cook <kees@kernel.org>]

$(cc-option-bit) returns the flag it was given when the compiler accepts
it, and an empty string otherwise. It was originally only used
internally for machine bit flags, but it is generally useful[1].

Rename it to $(cc-option-str), which says what it returns rather than
what it was first used for, and extract the probe logic from the existing
$(cc-option) macro to reuse it. Additionally add support for an optional
fallback, much like the Kbuild cc-option macro. This can be used as:

	config CC_OPT_FOO
		def_string "$(cc-option-str,-fnew-option,-fold-option)"

If the fallback is omitted, it is just an empty string.

Build tested ARCH=x86_64 defconfig with GCC 16.2.0.

Assisted-by: LLM
Signed-off-by: Kees Cook <kees@kernel.org>
---
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nicolas Schier <nsc@kernel.org>
Cc: Julian Braha <julianbraha@gmail.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Miguel Ojeda <ojeda@kernel.org>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: "Borislav Petkov (AMD)" <bp@alien8.de>
Cc: Gary Guo <gary@garyguo.net>
Cc: "Thomas Weißschuh" <thomas.weissschuh@linutronix.de>
Cc: <linux-kbuild@vger.kernel.org>
---
 scripts/Kconfig.include | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/scripts/Kconfig.include b/scripts/Kconfig.include
index fc10671c297c..4ef2b64e97be 100644
--- a/scripts/Kconfig.include
+++ b/scripts/Kconfig.include
@@ -23,9 +23,19 @@ success = $(if-success,$(1),y,n)
 # Return n if <command> exits with 0, y otherwise
 failure = $(if-success,$(1),n,y)
 
+# $(cc-probe,<flag>)
+# The command $(cc-option) and $(cc-option-str) test <flag> with. Not meant
+# to be called directly; use one of those two instead.
+cc-probe = trap "rm -rf .tmp_$$" EXIT; mkdir .tmp_$$; $(CC) -Werror $(CLANG_FLAGS) $(1) -c -x c /dev/null -o .tmp_$$/tmp.o
+
 # $(cc-option,<flag>)
 # Return y if the compiler supports <flag>, n otherwise
-cc-option = $(success,trap "rm -rf .tmp_$$" EXIT; mkdir .tmp_$$; $(CC) -Werror $(CLANG_FLAGS) $(1) -c -x c /dev/null -o .tmp_$$/tmp.o)
+cc-option = $(success,$(cc-probe,$(1)))
+
+# $(cc-option-str,<flag>[,<fallback>])
+# Return <flag> if the compiler supports it, <fallback> otherwise.
+# <fallback> defaults to an empty string and is returned untested.
+cc-option-str = $(if-success,$(cc-probe,$(1)),$(1),$(2))
 
 # $(ld-option,<flag>)
 # Return y if the linker supports <flag>, n otherwise
@@ -61,9 +71,8 @@ ld-version := $(shell,set -- $(ld-info) && echo $2)
 # machine bit flags
 #  $(m32-flag): -m32 if the compiler supports it, or an empty string otherwise.
 #  $(m64-flag): -m64 if the compiler supports it, or an empty string otherwise.
-cc-option-bit = $(if-success,$(CC) -Werror $(1) -E -x c /dev/null -o /dev/null,$(1))
-m32-flag := $(cc-option-bit,-m32)
-m64-flag := $(cc-option-bit,-m64)
+m32-flag := $(cc-option-str,-m32)
+m64-flag := $(cc-option-str,-m64)
 
 # Test whether the compiler can link userspace applications
 cc_can_link_user = $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(1))
-- 
2.34.1