ARM: fix backtrace

Recent kernels have changed their behaviour to be more inconsistent
when handling printk continuations.  With todays kernels, the output
looks sane on the console, but dmesg splits individual printk()s which
do not have the KERN_CONT prefix into separate lines.

Since the assembly code is not trivial to add the KERN_CONT, and we
ideally want to avoid using KERN_CONT (as multiple printk()s can race
between different threads), convert the assembly dumping the register
values to C code, and have the C code build the output a line at a
time before dumping to the console.

This avoids the KERN_CONT issue, and also avoids situations where the
output is intermixed with other console activity.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

2 files changed, 23 insertions, 34 deletions

diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index bc698383e822..9688ec0c6ef4 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -74,6 +74,26 @@ void dump_backtrace_entry(unsigned long where, unsigned long from, unsigned long
                 dump_mem("", "Exception stack", frame + 4, frame + 4 + sizeof(struct pt_regs));
 }
 
+void dump_backtrace_stm(u32 *stack, u32 instruction)
+{
+        char str[80], *p;
+        unsigned int x;
+        int reg;
+
+        for (reg = 10, x = 0, p = str; reg >= 0; reg--) {
+                if (instruction & BIT(reg)) {
+                        p += sprintf(p, " r%d:%08x", reg, *stack--);
+                        if (++x == 6) {
+                                x = 0;
+                                p = str;
+                                printk("%s\n", str);
+                        }
+                }
+        }
+        if (p != str)
+                printk("%s\n", str);
+}
+
 #ifndef CONFIG_ARM_UNWIND
 /*
  * Stack pointers should always be within the kernels view of
diff --git a/arch/arm/lib/backtrace.S b/arch/arm/lib/backtrace.S
index fab5a50503ae..7d7952e5a3b1 100644
--- a/arch/arm/lib/backtrace.S
+++ b/arch/arm/lib/backtrace.S
@@ -10,6 +10,7 @@
  * 27/03/03 Ian Molton Clean up CONFIG_CPU
  *
  */
+#include <linux/kern_levels.h>
 #include <linux/linkage.h>
 #include <asm/assembler.h>
                 .text
@@ -83,13 +84,13 @@ for_each_frame:	tst	frame, mask		@ Check for address exceptions
                 teq     r3, r1, lsr #11
                 ldreq   r0, [frame, #-8]        @ get sp
                 subeq   r0, r0, #4              @ point at the last arg
-                bleq    .Ldumpstm               @ dump saved registers
+                bleq    dump_backtrace_stm      @ dump saved registers
 
 1004:           ldr     r1, [sv_pc, #0]         @ if stmfd sp!, {..., fp, ip, lr, pc}
                 ldr     r3, .Ldsi               @ instruction exists,
                 teq     r3, r1, lsr #11
                 subeq   r0, frame, #16
-                bleq    .Ldumpstm               @ dump saved registers
+                bleq    dump_backtrace_stm      @ dump saved registers
 
                 teq     sv_fp, #0               @ zero saved fp means
                 beq     no_frame                @ no further frames
@@ -112,38 +113,6 @@ ENDPROC(c_backtrace)
                 .long   1004b, 1006b
                 .popsection
 
-#define instr r4
-#define reg   r5
-#define stack r6
-
-.Ldumpstm:      stmfd   sp!, {instr, reg, stack, r7, lr}
-                mov     stack, r0
-                mov     instr, r1
-                mov     reg, #10
-                mov     r7, #0
-1:              mov     r3, #1
- ARM(           tst     instr, r3, lsl reg      )
- THUMB(         lsl     r3, reg                 )
- THUMB(         tst     instr, r3               )
-                beq     2f
-                add     r7, r7, #1
-                teq     r7, #6
-                moveq   r7, #0
-                adr     r3, .Lcr
-                addne   r3, r3, #1              @ skip newline
-                ldr     r2, [stack], #-4
-                mov     r1, reg
-                adr     r0, .Lfp
-                bl      printk
-2:              subs    reg, reg, #1
-                bpl     1b
-                teq     r7, #0
-                adrne   r0, .Lcr
-                blne    printk
-                ldmfd   sp!, {instr, reg, stack, r7, pc}
-
-.Lfp:           .asciz  " r%d:%08x%s"
-.Lcr:           .asciz  "\n"
 .Lbad:          .asciz  "Backtrace aborted due to bad frame pointer <%p>\n"
                 .align
 .Ldsi:          .word   0xe92dd800 >> 11        @ stmfd sp!, {... fp, ip, lr, pc}