Subject: [kvm-unit-tests PATCH 04/32] powerpc: interrupt stack backtracing

From: Nicholas Piggin <[email-masked]>
Date: Mon, 26 Feb 2024 20:11:50 +1000

Add support for backtracing across interrupt stacks, and
add interrupt frame backtrace for unhandled interrupts.

Signed-off-by: Nicholas Piggin <[email-masked]>
---
 lib/powerpc/processor.c |  4 ++-
 lib/ppc64/asm/stack.h   |  3 +++
 lib/ppc64/stack.c       | 55 +++++++++++++++++++++++++++++++++++++++++
 powerpc/Makefile.ppc64  |  1 +
 powerpc/cstart64.S      |  7 ++++--
 5 files changed, 67 insertions(+), 3 deletions(-)
 create mode 100644 lib/ppc64/stack.c

diff --git a/lib/powerpc/processor.c b/lib/powerpc/processor.c
index ad0d95666..114584024 100644
--- a/lib/powerpc/processor.c
+++ b/lib/powerpc/processor.c
@@ -51,7 +51,9 @@ void do_handle_exception(struct pt_regs *regs)
 		return;
 	}
 
-	printf("unhandled cpu exception %#lx at NIA:0x%016lx MSR:0x%016lx\n", regs->trap, regs->nip, regs->msr);
+	printf("Unhandled cpu exception %#lx at NIA:0x%016lx MSR:0x%016lx\n",
+			regs->trap, regs->nip, regs->msr);
+	dump_frame_stack((void *)regs->nip, (void *)regs->gpr[1]);
 	abort();
 }
 
diff --git a/lib/ppc64/asm/stack.h b/lib/ppc64/asm/stack.h
index 9734bbb8f..94fd1021c 100644
--- a/lib/ppc64/asm/stack.h
+++ b/lib/ppc64/asm/stack.h
@@ -5,4 +5,7 @@
 #error Do not directly include <asm/stack.h>. Just use <stack.h>.
 #endif
 
+#define HAVE_ARCH_BACKTRACE
+#define HAVE_ARCH_BACKTRACE_FRAME
+
 #endif
diff --git a/lib/ppc64/stack.c b/lib/ppc64/stack.c
new file mode 100644
index 000000000..fcb7fa860
--- /dev/null
+++ b/lib/ppc64/stack.c
@@ -0,0 +1,55 @@
+#include <libcflat.h>
+#include <asm/ptrace.h>
+#include <stack.h>
+
+extern char exception_stack_marker[];
+
+int backtrace_frame(const void *frame, const void **return_addrs, int max_depth)
+{
+	static int walking;
+	int depth = 0;
+	const unsigned long *bp = (unsigned long *)frame;
+	void *return_addr;
+
+	asm volatile("" ::: "lr"); /* Force it to save LR */
+
+	if (walking) {
+		printf("RECURSIVE STACK WALK!!!\n");
+		return 0;
+	}
+	walking = 1;
+
+	bp = (unsigned long *)bp[0];
+	return_addr = (void *)bp[2];
+
+	for (depth = 0; bp && depth < max_depth; depth++) {
+		return_addrs[depth] = return_addr;
+		if (return_addrs[depth] == 0)
+			break;
+		if (return_addrs[depth] == exception_stack_marker) {
+			struct pt_regs *regs;
+
+			regs = (void *)bp + STACK_FRAME_OVERHEAD;
+			bp = (unsigned long *)bp[0];
+			/* Represent interrupt frame with vector number */
+			return_addr = (void *)regs->trap;
+			if (depth + 1 < max_depth) {
+				depth++;
+				return_addrs[depth] = return_addr;
+				return_addr = (void *)regs->nip;
+			}
+		} else {
+			bp = (unsigned long *)bp[0];
+			return_addr = (void *)bp[2];
+		}
+	}
+
+	walking = 0;
+	return depth;
+}
+
+int backtrace(const void **return_addrs, int max_depth)
+{
+	return backtrace_frame(__builtin_frame_address(0), return_addrs,
+			       max_depth);
+}
diff --git a/powerpc/Makefile.ppc64 b/powerpc/Makefile.ppc64
index b0ed2b104..eb682c226 100644
--- a/powerpc/Makefile.ppc64
+++ b/powerpc/Makefile.ppc64
@@ -17,6 +17,7 @@ cstart.o = $(TEST_DIR)/cstart64.o
 reloc.o  = $(TEST_DIR)/reloc64.o
 
 OBJDIRS += lib/ppc64
+cflatobjs += lib/ppc64/stack.o
 
 # ppc64 specific tests
 tests = $(TEST_DIR)/spapr_vpa.elf
diff --git a/powerpc/cstart64.S b/powerpc/cstart64.S
index 14ab0c6c8..278af84a6 100644
--- a/powerpc/cstart64.S
+++ b/powerpc/cstart64.S
@@ -188,6 +188,7 @@ call_handler:
 	.endr
 	mfsprg1	r0
 	std	r0,GPR1(r1)
+	std	r0,0(r1)
 
 	/* lr, xer, ccr */
 
@@ -206,12 +207,12 @@ call_handler:
 	subi	r31, r31, 0b - start_text
 	ld	r2, (p_toc_text - start_text)(r31)
 
-	/* FIXME: build stack frame */
-
 	/* call generic handler */
 
 	addi	r3,r1,STACK_FRAME_OVERHEAD
 	bl	do_handle_exception
+	.global exception_stack_marker
+exception_stack_marker:
 
 	/* restore context */
 
@@ -321,6 +322,7 @@ handler_trampoline:
 	/* nip and msr */
 	mfsrr0	r0
 	std	r0, _NIP(r1)
+	std	r0, INT_FRAME_SIZE+16(r1)
 
 	mfsrr1	r0
 	std	r0, _MSR(r1)
@@ -337,6 +339,7 @@ handler_htrampoline:
 	/* nip and msr */
 	mfspr	r0, SPR_HSRR0
 	std	r0, _NIP(r1)
+	std	r0, INT_FRAME_SIZE+16(r1)
 
 	mfspr	r0, SPR_HSRR1
 	std	r0, _MSR(r1)
-- 
2.42.0