On 08/11/2015 11:57 PM, Jungseok Lee wrote:
On Aug 4, 2015, at 4:44 PM, AKASHI Takahiro wrote:
Hi Akashi,
On arm64, an exception handler use the same stack as in non-exception
contexts, but doesn't create a stack frame for elx_xx entry, only updating
sp register. This behavior results in save_stace_trace() missing a function
that is the one when an exception happens.
This patch creates a stack frame for this case, and puts an additional
entry for the function in a stack trace list.
Signed-off-by: AKASHI Takahiro <takahiro.aka...@linaro.org>
---
arch/arm64/kernel/entry.S | 4 ++++
arch/arm64/kernel/stacktrace.c | 17 +++++++++++++++++
2 files changed, 21 insertions(+)
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index f860bfd..aacb6c6 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -107,6 +107,8 @@
str x21, [sp, #S_SYSCALLNO]
.endif
+ /* create a stack frame for stack tracer */
+ mov x29, sp
/*
* Registers that may be useful after this macro is invoked:
*
@@ -737,3 +739,5 @@ ENTRY(sys_rt_sigreturn_wrapper)
mov x0, sp
b sys_rt_sigreturn
ENDPROC(sys_rt_sigreturn_wrapper)
+
+ENTRY(end_of_vectors)
diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index d1790eb..22ce7c9 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -25,6 +25,10 @@
#include <asm/stacktrace.h>
#define S_FRAME_SIZE sizeof(struct pt_regs) /* asm-offsets.h */
+#define S_FP offsetof(struct pt_regs, regs[29])
+#define S_LR offsetof(struct pt_regs, regs[30])
+
+extern unsigned int *vectors, *end_of_vectors;
/*
* AArch64 PCS assigns the frame pointer to x29.
@@ -50,6 +54,19 @@ int notrace unwind_frame(struct stackframe *frame)
if (fp < low || fp > high - 0x18 || fp & 0xf)
return -EINVAL;
+ if ((frame->pc >= (unsigned long)&vectors) &&
+ (frame->pc < (unsigned long)&end_of_vectors)) {
+ /*
+ * Expection handler does not use a normal format of
+ * stack frame, but allocates struct pt_regs.
+ */
+ frame->sp = frame->sp + S_FRAME_SIZE;
+ frame->fp = *(unsigned long *)(fp + S_FP);
+ frame->pc = *(unsigned long *)(fp + S_LR);
Not frame->pc = *(unsigned long *)(fp + S_PC)? Don't we need to look up elr_el1
since this is an exception?
You are right. Will fix it if I submit the next version.
+
+ return 0;
+ }
+
frame->sp = fp + 0x10;
I'm just curious about this constant, 0x10. Do you have an idea on this value?
As reviewing objdump of vmlinux, it looks needed to analyze the first store-pair
instruction of each function.
Please correct me if I'm wrong.
I don't know Catalin's intention here, but fp always points to saved pair of
<fp, lr> and so, in general, "fp + 0x10" is the address of succeeding local
variables
in callee function. (Remember my acsii art :)
This can be the easily-approximated (but not accurate) stack pointer of caller
unless
we decode function prologues.
Thanks,
-Takahiro AKASHI
Best Regards
Jungseok Lee
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