arch: riscv: Implement perf stack thrace func

Implement stack trace function for riscv arch, that get required
thread register values and unwind stack with it.

Signed-off-by: Mikhail Kushnerov <[email protected]>

Author: Mikhail Kushnerov

arch/riscv/core/CMakeLists.txt

@@ -27,3 +27,4 @@ zephyr_library_sources_ifdef(CONFIG_USERSPACE userspace.S)
 zephyr_library_sources_ifdef(CONFIG_SEMIHOST semihost.c)
 zephyr_library_sources_ifdef(CONFIG_EXCEPTION_STACK_TRACE stacktrace.c)
 zephyr_linker_sources(ROM_START SORT_KEY 0x0vectors vector_table.ld)
+zephyr_library_sources_ifdef(CONFIG_PROFILING_PERF perf.c)

arch/riscv/core/perf.c

@@ -0,0 +1,93 @@
+/*
+ *  Copyright (c) 2023 KNS Group LLC (YADRO)
+ *
+ *  SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <zephyr/kernel.h>
+
+static bool valid_stack(uintptr_t addr, k_tid_t current)
+{
+	return current->stack_info.start <= addr &&
+		addr < current->stack_info.start + current->stack_info.size;
+}
+
+/*
+ * This function use frame pointers to unwind stack and get trace of return addresses.
+ * Return addresses are translated in corresponding function's names using .elf file.
+ * So we get function call trace
+ */
+size_t arch_perf_current_stack_trace(uintptr_t *buf, size_t size)
+{
+	if (size < 2U)
+		return 0;
+
+	size_t idx = 0;
+
+	/*
+	 * In riscv (arch/riscv/core/isr.S) ra, ip($mepc) and fp($s0) are saved
+	 * at the beginning of _isr_wrapper in order, specified by z_arch_esf_t.
+	 * Then, before calling interruption handler, core switch $sp to
+	 * _current_cpu->irq_stack and save $sp with offset -16 on irq stack
+	 *
+	 * The following lines lines do the reverse things to get ra, ip anf fp
+	 * from thread stack
+	 */
+	const struct arch_esf * const esf =
+		*((struct arch_esf **)(((uintptr_t)_current_cpu->irq_stack) - 16));
+
+	/*
+	 * $s0 is used as frame pointer.
+	 *
+	 * stack frame in memory (commonly):
+	 * (addresses growth up)
+	 *  ....
+	 *  [-] <- $fp($s0) (curr)
+	 *  $ra
+	 *  $fp($s0) (next)
+	 *  ....
+	 *
+	 * If function do not call any other function, compiller may not save $ra,
+	 * then stack frame will be:
+	 *  ....
+	 *  [-] <- $fp($s0) (curr)
+	 *  $fp($s0) (next)
+	 *  ....
+	 *
+	 */
+	void **fp = (void **)esf->s0;
+	void **new_fp = (void **)fp[-1];
+
+	buf[idx++] = (uintptr_t)esf->mepc;
+
+	/*
+	 * During function prologue and epilogue fp is equal to fp of
+	 * previous function stack frame, it looks like second function
+	 * from top is missed.
+	 * So saving $ra will help in case when irq occurred in
+	 * function prologue or epilogue.
+	 */
+	buf[idx++] = (uintptr_t)esf->ra;
+	if (valid_stack((uintptr_t)new_fp, _current)) {
+		fp = new_fp;
+	}
+	while (valid_stack((uintptr_t)fp, _current)) {
+		if (idx >= size)
+			return 0;
+
+		buf[idx++] = (uintptr_t)fp[-1];
+		new_fp = (void **)fp[-2];
+
+		/*
+		 * anti-infinity-loop if
+		 * new_fp can't be smaller than fp, cause the stack is growing down
+		 * and trace moves deeper into the stack
+		 */
+		if (new_fp <= fp) {
+			break;
+		}
+		fp = new_fp;
+	}
+
+	return idx;
+}