[PATCH] selftests/nolibc: make stackprotector probing more robust

["Thomas Weißschuh" <linux@weissschuh.net>]

nolibc only supports symbol-based stackprotectors, based on the global
variable __stack_chk_guard. Support for this differs between
architectures and toolchains. Some use the symbol mode by default, some
require a flag to enable it and some don't support it at all.

Before the nolibc test Makefile required the availability of
"-mstack-protector-guard=global" to enable stackprotectors.
While this flag makes sure that the correct mode is available it doesn't
work where the correct mode is the only supported one and therefore the
flag is not implemented.

Switch to a more dynamic probing mechanism.
This correctly enables stack protectors for mips, loongarch and m68k.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
 tools/testing/selftests/nolibc/Makefile | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/nolibc/Makefile b/tools/testing/selftests/nolibc/Makefile
index 94176ffe46463548cc9bc787933b6cefa83d6502..853f3a846d4c0fb187922d3063ec3d1a9a30ae46 100644
--- a/tools/testing/selftests/nolibc/Makefile
+++ b/tools/testing/selftests/nolibc/Makefile
@@ -195,7 +195,10 @@ CFLAGS_sparc32 = $(call cc-option,-m32)
 ifeq ($(origin XARCH),command line)
 CFLAGS_XARCH = $(CFLAGS_$(XARCH))
 endif
-CFLAGS_STACKPROTECTOR ?= $(call cc-option,-mstack-protector-guard=global $(call cc-option,-fstack-protector-all))
+_CFLAGS_STACKPROTECTOR = $(call cc-option,-fstack-protector-all) $(call cc-option,-mstack-protector-guard=global)
+CFLAGS_STACKPROTECTOR ?= $(call try-run, \
+	echo 'void foo(void) {}' | $(CC) -x c - -o - -S $(_CFLAGS_STACKPROTECTOR) | grep -q __stack_chk_guard, \
+	$(_CFLAGS_STACKPROTECTOR))
 CFLAGS_SANITIZER ?= $(call cc-option,-fsanitize=undefined -fsanitize-trap=all)
 CFLAGS  ?= -Os -fno-ident -fno-asynchronous-unwind-tables -std=c89 -W -Wall -Wextra \
 		$(call cc-option,-fno-stack-protector) $(call cc-option,-Wmissing-prototypes) \

---
base-commit: 19272b37aa4f83ca52bdf9c16d5d81bdd1354494
change-id: 20250530-nolibc-stackprotector-robust-77c9f55a3921

Best regards,
-- 
Thomas Weißschuh <linux@weissschuh.net>