[kvm-unit-tests PATCH v8 10/35] powerpc: interrupt stack backtracing

[Nicholas Piggin]

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

This requires a back-chain created from initial interrupt stack
frame to the r1 value of the interrupted context. A label is
added at the return location of the exception handler call, so
the unwinder can recognize the initial interrupt frame.

The additional cstart entry-frame is no longer required because
the unwinder now looks for frame == 0 as well as address == 0.

Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
 lib/powerpc/processor.c |  4 +++-
 lib/ppc64/asm/stack.h   |  3 +++
 lib/ppc64/stack.c       | 53 +++++++++++++++++++++++++++++++++++++++++
 powerpc/Makefile.ppc64  |  1 +
 powerpc/cstart64.S      | 15 +++---------
 5 files changed, 63 insertions(+), 13 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..e6f259de7
--- /dev/null
+++ b/lib/ppc64/stack.c
@@ -0,0 +1,53 @@
+#include <libcflat.h>
+#include <asm/ptrace.h>
+#include <stack.h>
+
+extern char do_handle_exception_return[];
+
+int arch_backtrace_frame(const void *frame, const void **return_addrs,
+			 int max_depth, bool current_frame)
+{
+	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;
+
+	if (current_frame)
+		bp = __builtin_frame_address(0);
+
+	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] == do_handle_exception_return) {
+			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;
+}
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 80baabe8f..07d297f61 100644
--- a/powerpc/cstart64.S
+++ b/powerpc/cstart64.S
@@ -51,16 +51,6 @@ start:
 	std	r0,0(r1)
 	std	r0,16(r1)
 
-	/*
-	 * Create entry frame of 64-bytes, same as the initial frame. A callee
-	 * may use the caller frame to store LR, and backtrace() termination
-	 * looks for return address == NULL, so the initial stack frame can't
-	 * be used to call C or else it could overwrite the zeroed LR save slot
-	 * and break backtrace termination.  This frame would be unnecessary if
-	 * backtrace looked for a zeroed frame address.
-	 */
-	stdu	r1,-64(r1)
-
 	/* save DTB pointer */
 	std	r3, 56(r1)
 
@@ -195,6 +185,7 @@ call_handler:
 	.endr
 	mfsprg1	r0
 	std	r0,GPR1(r1)
+	std	r0,0(r1) /* Backchain from interrupt stack to regular stack */
 
 	/* lr, xer, ccr */
 
@@ -213,12 +204,12 @@ 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 do_handle_exception_return
+do_handle_exception_return:
 
 	/* restore context */
 
-- 
2.43.0