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ARM: fix backtrace

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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>
This commit is contained in:
Russell King 2016-11-15 13:55:59 +00:00
parent 6127d124ee
commit 24c66dfd56
2 changed files with 23 additions and 34 deletions
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20
arch/arm/kernel/traps.c
View File

@ -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

37
arch/arm/lib/backtrace.S
View File

@ -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}