[kvm-unit-tests PATCH v3 4/7] s390x: Provide preliminary backtrace support

Janosch Frank
2021-02-22T12:35:34Z

After the stack changes we can finally use -mbackchain and have a
working backtrace.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
---
lib/s390x/stack.c | 20 ++++++++++++++------
s390x/Makefile | 1 +
s390x/macros.S | 5 +++++
3 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/lib/s390x/stack.c b/lib/s390x/stack.c
index 0fcd1afb..4cf80dae 100644
--- a/lib/s390x/stack.c
+++ b/lib/s390x/stack.c
@@ -3,24 +3,32 @@
* s390x stack implementation
*
* Copyright (c) 2017 Red Hat Inc
+ * Copyright 2021 IBM Corp
*
* Authors:
* Thomas Huth <thuth@redhat.com>
* David Hildenbrand <david@redhat.com>
+ * Janosch Frank <frankja@de.ibm.com>
*/
#include <libcflat.h>
#include <stack.h>
+#include <asm/arch_def.h>

int backtrace_frame(const void *frame, const void **return_addrs, int max_depth)
{
- printf("TODO: Implement backtrace_frame(%p, %p, %d) function!\n",
- frame, return_addrs, max_depth);
- return 0;
+ int depth = 0;
+ struct stack_frame *stack = (struct stack_frame *)frame;
+
+ for (depth = 0; stack && depth < max_depth; depth++) {
+ return_addrs[depth] = (void *)stack->grs[8];
+ stack = stack->back_chain;
+ }
+
+ return depth;
}

int backtrace(const void **return_addrs, int max_depth)
{
- printf("TODO: Implement backtrace(%p, %d) function!\n",
- return_addrs, max_depth);
- return 0;
+ return backtrace_frame(__builtin_frame_address(0),
+ return_addrs, max_depth);
}
diff --git a/s390x/Makefile b/s390x/Makefile
index f3b0fccf..20bb5683 100644
--- a/s390x/Makefile
+++ b/s390x/Makefile
@@ -39,6 +39,7 @@ CFLAGS += -ffreestanding
CFLAGS += -I $(SRCDIR)/lib -I $(SRCDIR)/lib/s390x -I lib
CFLAGS += -O2
CFLAGS += -march=zEC12
+CFLAGS += -mbackchain
CFLAGS += -fno-delete-null-pointer-checks
LDFLAGS += -nostdlib -Wl,--build-id=none

diff --git a/s390x/macros.S b/s390x/macros.S
index 11f4397a..d4f41ec4 100644
--- a/s390x/macros.S
+++ b/s390x/macros.S
@@ -22,6 +22,11 @@
lgr %r2, %r15
/* Allocate stack space for called C function, as specified in s390 ELF ABI */
slgfi %r15, 160
+ /*
+ * Save the address of the interrupt stack into the back chain
+ * of the called function.
+ */
+ stg %r2, STACK_FRAME_INT_BACKCHAIN(%r15)
brasl %r14, \c_func
algfi %r15, 160
RESTORE_REGS_STACK
--
2.25.1