[kvm-unit-tests PATCH v2 3/6] arm64: enable frame pointer and support stack unwinding

[Nadav Amit <nadav.amit@gmail.com>]

From: Nadav Amit <namit@vmware.com>

Enable frame pointers for arm64 and perform stack unwinding based on
arm64 convention.

Signed-off-by: Nadav Amit <namit@vmware.com>

---
v1->v2:
* Adding SPDX [checkpatch]
* Moving some unused declarations to next patch [Andrew]
* Adding recursion prevention
---
 arm/Makefile.arm      |  3 ---
 arm/Makefile.arm64    |  1 +
 arm/Makefile.common   |  3 +++
 lib/arm64/asm/stack.h |  3 +++
 lib/arm64/stack.c     | 44 +++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 51 insertions(+), 3 deletions(-)
 create mode 100644 lib/arm64/stack.c

diff --git a/arm/Makefile.arm b/arm/Makefile.arm
index 2ce00f5..7fd39f3 100644
--- a/arm/Makefile.arm
+++ b/arm/Makefile.arm
@@ -11,9 +11,6 @@ ifeq ($(CONFIG_EFI),y)
 $(error Cannot build arm32 tests as EFI apps)
 endif
 
-# stack.o relies on frame pointers.
-KEEP_FRAME_POINTER := y
-
 CFLAGS += $(machine)
 CFLAGS += -mcpu=$(PROCESSOR)
 CFLAGS += -mno-unaligned-access
diff --git a/arm/Makefile.arm64 b/arm/Makefile.arm64
index eada7f9..60385e2 100644
--- a/arm/Makefile.arm64
+++ b/arm/Makefile.arm64
@@ -21,6 +21,7 @@ define arch_elf_check =
 endef
 
 cstart.o = $(TEST_DIR)/cstart64.o
+cflatobjs += lib/arm64/stack.o
 cflatobjs += lib/arm64/processor.o
 cflatobjs += lib/arm64/spinlock.o
 cflatobjs += lib/arm64/gic-v3-its.o lib/arm64/gic-v3-its-cmd.o
diff --git a/arm/Makefile.common b/arm/Makefile.common
index 9b45a8f..bc86e44 100644
--- a/arm/Makefile.common
+++ b/arm/Makefile.common
@@ -22,6 +22,9 @@ $(TEST_DIR)/sieve.elf: AUXFLAGS = 0x1
 ##################################################################
 AUXFLAGS ?= 0x0
 
+# stack.o relies on frame pointers.
+KEEP_FRAME_POINTER := y
+
 CFLAGS += -std=gnu99
 CFLAGS += -ffreestanding
 CFLAGS += -O2
diff --git a/lib/arm64/asm/stack.h b/lib/arm64/asm/stack.h
index d000624..be486cf 100644
--- a/lib/arm64/asm/stack.h
+++ b/lib/arm64/asm/stack.h
@@ -5,4 +5,7 @@
 #error Do not directly include <asm/stack.h>. Just use <stack.h>.
 #endif
 
+#define HAVE_ARCH_BACKTRACE_FRAME
+#define HAVE_ARCH_BACKTRACE
+
 #endif
diff --git a/lib/arm64/stack.c b/lib/arm64/stack.c
new file mode 100644
index 0000000..a2024e8
--- /dev/null
+++ b/lib/arm64/stack.c
@@ -0,0 +1,44 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Backtrace support.
+ */
+#include <libcflat.h>
+#include <stdbool.h>
+#include <stack.h>
+
+int backtrace_frame(const void *frame, const void **return_addrs, int max_depth)
+{
+	const void *fp = frame;
+	static bool walking;
+	void *lr;
+	int depth;
+
+	if (walking) {
+		printf("RECURSIVE STACK WALK!!!\n");
+		return 0;
+	}
+	walking = true;
+
+	/*
+	 * ARM64 stack grows down. fp points to the previous fp on the stack,
+	 * and lr is just above it
+	 */
+	for (depth = 0; fp && depth < max_depth; ++depth) {
+
+		asm volatile ("ldp %0, %1, [%2]"
+				  : "=r" (fp), "=r" (lr)
+				  : "r" (fp)
+				  : );
+
+		return_addrs[depth] = lr;
+	}
+
+	walking = false;
+	return depth;
+}
+
+int backtrace(const void **return_addrs, int max_depth)
+{
+	return backtrace_frame(__builtin_frame_address(0),
+			       return_addrs, max_depth);
+}
-- 
2.34.1