[PATCH v2] perf test: Make leafloop workload immune to compiler options

[James Clark]

Since the leafloop test program was moved into the main Perf binary as a
workload, it inherited the same compiler options as Perf. In this case
the -fstack-protector option broke the assumption that simple leaf
frames don't have a stack frame on Arm. This causes
test_arm_callgraph_fp.sh to pass even if the stack isn't augmented with
the link register, making the test useless.

Fix it by rewriting the leaf function in assembly seeing as it's so
simple. Adding -fno-stack-protector would also work, but wouldn't be
robust against other future compiler option additions.

The local variables and 'a' variable were never needed so remove them to
simplify.

Assisted-by: GitHub-Copilot:GPT-5.5
Signed-off-by: James Clark <james.clark@xxxxxxxxxx>
---
Changes in v2:
- Push and pop asm sections - (Sashiko)
- Add .size directive - (Sashiko)
- Add asm label for done and test with LTO enabled - (Sashiko)
- Link to v1: https://lore.kernel.org/r/20260508-james-perf-leafloop-stack-v1-1-637c260b2da8@xxxxxxxxxx
---
 tools/perf/tests/workloads/leafloop.c | 40 +++++++++++++++++++++++++++--------
 1 file changed, 31 insertions(+), 9 deletions(-)

diff --git a/tools/perf/tests/workloads/leafloop.c b/tools/perf/tests/workloads/leafloop.c
index f7561767e32c..c20c75f7ba49 100644
--- a/tools/perf/tests/workloads/leafloop.c
+++ b/tools/perf/tests/workloads/leafloop.c
@@ -6,26 +6,48 @@
 #include "../tests.h"
 
 /* We want to check these symbols in perf script */
-noinline void leaf(volatile int b);
-noinline void parent(volatile int b);
+noinline void leaf(void);
+noinline void parent(void);
 
-static volatile int a;
-static volatile sig_atomic_t done;
+static volatile sig_atomic_t done asm("leafloop_done");
 
 static void sighandler(int sig __maybe_unused)
 {
 	done = 1;
 }
 
-noinline void leaf(volatile int b)
+#if defined(__aarch64__)
+/*
+ * Write leaf() in assembly so it stays as a minimal leaf function with no
+ * stack frame and won't get silently broken in the future by any Perf wide
+ * compilation options like -fstack-protector-all.
+ */
+asm(
+	".pushsection .text,\"ax\",%progbits\n"
+	".global leaf\n"
+	".type leaf, %function\n"
+	"leaf:\n"
+	"	adrp	x1, leafloop_done\n"
+	"	ldr	w2, [x1, #:lo12:leafloop_done]\n"
+	"	cbz	w2, leaf\n"
+	"	ret\n"
+	".size leaf, .-leaf\n"
+	".popsection\n"
+);
+
+#else
+
+noinline void leaf(void)
 {
 	while (!done)
-		a += b;
+		;
 }
 
-noinline void parent(volatile int b)
+#endif
+
+noinline void parent(void)
 {
-	leaf(b);
+	leaf();
 }
 
 static int leafloop(int argc, const char **argv)
@@ -39,7 +61,7 @@ static int leafloop(int argc, const char **argv)
 	signal(SIGALRM, sighandler);
 	alarm(sec);
 
-	parent(sec);
+	parent();
 	return 0;
 }
 

---
base-commit: 8c8f2093614373ea8179b562320212a25cf937c0
change-id: 20260508-james-perf-leafloop-stack-c221600eddf2

Best regards,
-- 
James Clark <james.clark@xxxxxxxxxx>