perf test: Make leafloop workload immune to compiler options

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.

Reviewed-by: Ian Rogers <irogers@google.com>
Assisted-by: GitHub-Copilot:GPT-5.5
Signed-off-by: James Clark <james.clark@linaro.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/tests/workloads/leafloop.c b/tools/perf/tests/workloads/leafloop.c
index f7561767e32cd284682fb15511a6212d58b3556e..c20c75f7ba49ec591229947db8aa561399141363 100644 (file)
--- 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;
 }