[Xen-devel] [PATCH] xen/arm64: fix stack dump in show_trace

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On aarch64 the frame pointer points to the next frame pointer and the return
address is the previous stack slot (so below on the downward growing stack,
therefore above in memory):

       |<RETURN ADDR>      ^addresses grow up
 FP -> |<NEXT FP>          |
       |                   |
       v                   |
       stack grows down.

This is contrary to aarch32 where the frame pointer points to the return
address and the next frame pointer is the next stack slot (so above on the
downward growing stack, below in memory):

 FP -> |<RETURN ADDR>       ^addresses grow up
       |<NEXT FP>           |
       |                    |
       v                    |
       stack grows down.

In addition print out LR as part of the trace, since it may contain the
penultimate return address e.g. if the ultimate function is a leaf function.

Lastly nuke some unnecessary braces.

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
---
 xen/arch/arm/traps.c |   69 +++++++++++++++++++++++++++++++------------------
 1 files changed, 44 insertions(+), 25 deletions(-)

diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
index 83a7fbc..398d209 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -519,7 +519,41 @@ static void show_guest_stack(struct cpu_user_regs *regs)
 }
 
 #define STACK_BEFORE_EXCEPTION(regs) ((register_t*)(regs)->sp)
-
+#ifdef CONFIG_ARM_32
+/* Frame pointer points to the return address:
+ * (largest address)
+ * | cpu_info
+ * | [...]                                   |
+ * | return addr      <-----------------,    |
+ * | fp --------------------------------+----'
+ * | [...]                              |
+ * | return addr      <------------,    |
+ * | fp ---------------------------+----'
+ * | [...]                         |
+ * | return addr      <- regs->fp  |
+ * | fp ---------------------------'
+ * |
+ * v (smallest address, sp)
+ */
+#define STACK_FRAME_BASE(fp)       ((register_t*)(fp) - 1)
+#else
+/* Frame pointer points to the next frame:
+ * (largest address)
+ * | cpu_info
+ * | [...]                                   |
+ * | return addr                             |
+ * | fp <-------------------------------, >--'
+ * | [...]                              |
+ * | return addr                        |
+ * | fp <--------------------------, >--'
+ * | [...]                         |
+ * | return addr      <- regs->fp  |
+ * | fp ---------------------------'
+ * |
+ * v (smallest address, sp)
+ */
+#define STACK_FRAME_BASE(fp)       ((register_t*)(fp))
+#endif
 static void show_trace(struct cpu_user_regs *regs)
 {
     register_t *frame, next, addr, low, high;
@@ -527,29 +561,15 @@ static void show_trace(struct cpu_user_regs *regs)
     printk("Xen call trace:\n   ");
 
     printk("[<%p>]", _p(regs->pc));
-    print_symbol(" %s\n   ", regs->pc);
+    print_symbol(" %s (PC)\n   ", regs->pc);
+    printk("[<%p>]", _p(regs->lr));
+    print_symbol(" %s (LR)\n   ", regs->lr);
 
     /* Bounds for range of valid frame pointer. */
-    low  = (register_t)(STACK_BEFORE_EXCEPTION(regs)/* - 2*/);
+    low  = (register_t)(STACK_BEFORE_EXCEPTION(regs));
     high = (low & ~(STACK_SIZE - 1)) +
         (STACK_SIZE - sizeof(struct cpu_info));
 
-    /* Frame:
-     * (largest address)
-     * | cpu_info
-     * | [...]                                   |
-     * | return addr      <-----------------,    |
-     * | fp --------------------------------+----'
-     * | [...]                              |
-     * | return addr      <------------,    |
-     * | fp ---------------------------+----'
-     * | [...]                         |
-     * | return addr      <- regs->fp  |
-     * | fp ---------------------------'
-     * |
-     * v (smallest address, sp)
-     */
-
     /* The initial frame pointer. */
     next = regs->fp;
 
@@ -557,12 +577,11 @@ static void show_trace(struct cpu_user_regs *regs)
     {
         if ( (next < low) || (next >= high) )
             break;
-        {
-            /* Ordinary stack frame. */
-            frame = (register_t *)next;
-            next  = frame[-1];
-            addr  = frame[0];
-        }
+
+        /* Ordinary stack frame. */
+        frame = STACK_FRAME_BASE(next);
+        next  = frame[0];
+        addr  = frame[1];
 
         printk("[<%p>]", _p(addr));
         print_symbol(" %s\n   ", addr);
-- 
1.7.2.5


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