Add a variant of compartment call benchmark that actually uses some s…

benchmarks/stack-usage/callee.cc

@@ -0,0 +1,15 @@
+#include "callee.h"
+#include "../timing.h"
+
+int  noop_return(size_t s) 
+{ 
+	use_stack(s);
+	return rdcycle(); 
+}
+
+int  noop_call(int start)
+{
+	int end = rdcycle();
+	check_stack_zeroed();
+	return end - start;
+}

benchmarks/stack-usage/callee.h

@@ -0,0 +1,4 @@
+#include <compartment.h>
+
+int __cheri_compartment("callee") noop_return(size_t s);
+int __cheri_compartment("callee") noop_call(int start);

benchmarks/stack-usage/caller.cc

@@ -0,0 +1,22 @@
+#include "../timing.h"
+#include "callee.h"
+#include <compartment.h>
+#include <locks.hh>
+
+void __cheri_compartment("caller") run()
+{
+	MessageBuilder<ImplicitUARTOutput> out;
+	out.format("#board\tstack_use\tcall\treturn\n");
+	for (size_t s = 1; s < 0x1000; s <<= 1)
+	{
+		auto [callPath, returnPath] = CHERI::with_interrupts_disabled([&]() {
+			use_stack(s);
+			auto callPath = noop_call(rdcycle());
+			auto returnPath = noop_return(s);
+			returnPath = rdcycle() - returnPath;
+			check_stack_zeroed();
+			return std::tuple{callPath, returnPath};
+		});
+		out.format(__XSTRING(BOARD) "\t{}\t{}\t{}\n", s, callPath, returnPath);
+	}
+}

benchmarks/stack-usage/xmake.lua

@@ -0,0 +1,39 @@
+-- Copyright Microsoft and CHERIoT Contributors.
+-- SPDX-License-Identifier: MIT
+
+set_project("CHERIoT stack-usage benchmark");
+sdkdir = "../../sdk"
+includes(sdkdir)
+set_toolchains("cheriot-clang")
+
+-- Support libraries
+includes(path.join(sdkdir, "lib/freestanding"),
+         path.join(sdkdir, "lib/atomic"),
+         path.join(sdkdir, "lib/crt"))
+
+option("board")
+    set_default("sail")
+
+compartment("callee")
+    add_files("callee.cc")
+
+compartment("caller")
+    add_defines("BOARD=" .. tostring(get_config("board")))
+    add_files("caller.cc")
+
+-- Firmware image for the example.
+firmware("stack-usage-benchmark")
+    add_deps("crt", "freestanding", "atomic")
+    add_deps("caller", "callee")
+    on_load(function(target)
+        target:values_set("board", "$(board)")
+        target:values_set("threads", {
+            {
+                compartment = "caller",
+                priority = 1,
+                entry_point = "run",
+                stack_size = 0x1000,
+                trusted_stack_frames = 3
+            }
+        }, {expand = false})
+    end)

benchmarks/timing.h

@@ -36,4 +36,28 @@ namespace
 		CHERI::Capability stack{cspRegister};
 		return stack.length();
 	}
+
+	void use_stack(size_t s)
+	{
+		volatile uint8_t stack_array[s];
+		stack_array[0] = 1;
+	}
+
+	void check_stack_zeroed()
+	{
+		register void **cspRegister asm("csp");
+		asm("" : "=C"(cspRegister));
+		CHERI::Capability stack{cspRegister};
+		CHERI::Capability<void*> stackP{stack};
+		stackP.address() = stack.base();
+		while(stackP.address() < stack.address())
+		{
+			CHERI::Capability<void> value{*stackP};
+			if (value != NULL)
+			{
+				__builtin_trap();
+			}
+			stackP += 1;
+		}
+	}
 } // namespace