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

Nicholas Piggin
2024-04-05T08:36:28Z

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@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