[MIPS] Improve unwind_stack()

This patch allows unwind_stack() to return ra for leaf function.
But it tries to detects cases where get_frame_info() wrongly
consider nested function as a leaf one.

It also pass 'unsinged long *sp' instead of 'unsigned long **sp'
as second parameter. The code looks cleaner.

Signed-off-by: Franck Bui-Huu <vagabon.xyz@gmail.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

2 files changed, 34 insertions, 25 deletions

diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
index 309bfa4a1520..951bf9ca3ce9 100644
--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -448,15 +448,16 @@ unsigned long get_wchan(struct task_struct *p)
 }
 
 #ifdef CONFIG_KALLSYMS
-/* used by show_frametrace() */
-unsigned long unwind_stack(struct task_struct *task,
-                           unsigned long **sp, unsigned long pc)
+/* used by show_backtrace() */
+unsigned long unwind_stack(struct task_struct *task, unsigned long *sp,
+                           unsigned long pc, unsigned long ra)
 {
         unsigned long stack_page;
         struct mips_frame_info info;
         char *modname;
         char namebuf[KSYM_NAME_LEN + 1];
         unsigned long size, ofs;
+        int leaf;
 
         stack_page = (unsigned long)task_stack_page(task);
         if (!stack_page)
@@ -469,18 +470,26 @@ unsigned long unwind_stack(struct task_struct *task,
 
         info.func = (void *)(pc - ofs);
         info.func_size = ofs;   /* analyze from start to ofs */
-        if (get_frame_info(&info)) {
-                /* leaf or unknown */
-                *sp += info.frame_size / sizeof(long);
+        leaf = get_frame_info(&info);
+        if (leaf < 0)
                 return 0;
-        }
-        if ((unsigned long)*sp < stack_page ||
-            (unsigned long)*sp + info.frame_size / sizeof(long) >
-            stack_page + THREAD_SIZE - 32)
+
+        if (*sp < stack_page ||
+            *sp + info.frame_size > stack_page + THREAD_SIZE - 32)
                 return 0;
 
-        pc = (*sp)[info.pc_offset];
-        *sp += info.frame_size / sizeof(long);
-        return pc;
+        if (leaf)
+                /*
+                 * For some extreme cases, get_frame_info() can
+                 * consider wrongly a nested function as a leaf
+                 * one. In that cases avoid to return always the
+                 * same value.
+                 */
+                pc = pc != ra ? ra : 0;
+        else
+                pc = ((unsigned long *)(*sp))[info.pc_offset];
+
+        *sp += info.frame_size;
+        return __kernel_text_address(pc) ? pc : 0;
 }
 #endif
diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
index 303f00843021..ab77034921c4 100644
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -74,8 +74,9 @@ void (*board_ejtag_handler_setup)(void);
 void (*board_bind_eic_interrupt)(int irq, int regset);
 
 
-static void show_raw_backtrace(unsigned long *sp)
+static void show_raw_backtrace(unsigned long reg29)
 {
+        unsigned long *sp = (unsigned long *)reg29;
         unsigned long addr;
 
         printk("Call Trace:");
@@ -99,30 +100,29 @@ static int __init set_raw_show_trace(char *str)
 }
 __setup("raw_show_trace", set_raw_show_trace);
 
-extern unsigned long unwind_stack(struct task_struct *task,
-                                  unsigned long **sp, unsigned long pc);
+extern unsigned long unwind_stack(struct task_struct *task, unsigned long *sp,
+                                  unsigned long pc, unsigned long ra);
+
 static void show_backtrace(struct task_struct *task, struct pt_regs *regs)
 {
-        unsigned long *sp = (long *)regs->regs[29];
+        unsigned long sp = regs->regs[29];
+        unsigned long ra = regs->regs[31];
         unsigned long pc = regs->cp0_epc;
-        int top = 1;
 
         if (raw_show_trace || !__kernel_text_address(pc)) {
                 show_raw_backtrace(sp);
                 return;
         }
         printk("Call Trace:\n");
-        while (__kernel_text_address(pc)) {
+        do {
                 print_ip_sym(pc);
-                pc = unwind_stack(task, &sp, pc);
-                if (top && pc == 0)
-                        pc = regs->regs[31];    /* leaf? */
-                top = 0;
-        }
+                pc = unwind_stack(task, &sp, pc, ra);
+                ra = 0;
+        } while (pc);
         printk("\n");
 }
 #else
-#define show_backtrace(task, r) show_raw_backtrace((long *)(r)->regs[29]);
+#define show_backtrace(task, r) show_raw_backtrace((r)->regs[29]);
 #endif
 
 /*