mirror of
https://github.com/AsahiLinux/u-boot
synced 2024-12-26 04:53:42 +00:00
ebfa2d2bce
Add link to usage/cmd/exception.rst. Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
184 lines
6.6 KiB
ReStructuredText
184 lines
6.6 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0+
|
|
.. Copyright (c) 2020 Heinrich Schuchardt
|
|
|
|
Analyzing crash dumps
|
|
=====================
|
|
|
|
When the CPU detects an instruction that it cannot execute it raises an
|
|
interrupt. U-Boot then writes a crash dump. This chapter describes how such
|
|
dump can be analyzed.
|
|
|
|
Creating a crash dump voluntarily
|
|
---------------------------------
|
|
|
|
For describing the analysis of a crash dump we need an example. U-Boot comes
|
|
with a command :doc:`exception <../usage/cmd/exception>` that comes in handy
|
|
here. The command is enabled by::
|
|
|
|
CONFIG_CMD_EXCEPTION=y
|
|
|
|
The example output below was recorded when running qemu\_arm64\_defconfig on
|
|
QEMU::
|
|
|
|
=> exception undefined
|
|
"Synchronous Abort" handler, esr 0x02000000
|
|
elr: 00000000000101fc lr : 00000000000214ec (reloc)
|
|
elr: 000000007ff291fc lr : 000000007ff3a4ec
|
|
x0 : 000000007ffbd7f8 x1 : 0000000000000000
|
|
x2 : 0000000000000001 x3 : 000000007eedce18
|
|
x4 : 000000007ff291fc x5 : 000000007eedce50
|
|
x6 : 0000000000000064 x7 : 000000007eedce10
|
|
x8 : 0000000000000000 x9 : 0000000000000004
|
|
x10: 6db6db6db6db6db7 x11: 000000000000000d
|
|
x12: 0000000000000006 x13: 000000000001869f
|
|
x14: 000000007edd7dc0 x15: 0000000000000002
|
|
x16: 000000007ff291fc x17: 0000000000000000
|
|
x18: 000000007eed8dc0 x19: 0000000000000000
|
|
x20: 000000007ffbd7f8 x21: 0000000000000000
|
|
x22: 000000007eedce10 x23: 0000000000000002
|
|
x24: 000000007ffd4c80 x25: 0000000000000000
|
|
x26: 0000000000000000 x27: 0000000000000000
|
|
x28: 000000007eedce70 x29: 000000007edd7b40
|
|
|
|
Code: b00003c0 912ad000 940029d6 17ffff52 (e7f7defb)
|
|
Resetting CPU ...
|
|
|
|
resetting ...
|
|
|
|
The first line provides us with the type of interrupt that occurred.
|
|
On ARMv8 a synchronous abort is an exception thrown when hitting an unallocated
|
|
instruction. The exception syndrome register ESR register contains information
|
|
describing the reason for the exception. Bit 25 set here indicates that a 32 bit
|
|
instruction led to the exception.
|
|
|
|
The second line provides the contents of the elr and the lr register after
|
|
subtracting the relocation offset. - U-Boot relocates itself after being
|
|
loaded. - The relocation offset can also be displayed using the bdinfo command.
|
|
|
|
After the contents of the registers we get a line indicating the machine
|
|
code of the instructions preceding the crash and in parentheses the instruction
|
|
leading to the dump.
|
|
|
|
Analyzing the code location
|
|
---------------------------
|
|
|
|
We can convert the instructions in the line starting with 'Code:' into mnemonics
|
|
using the objdump command. To make things easier scripts/decodecode is
|
|
supplied::
|
|
|
|
$echo 'Code: b00003c0 912ad000 940029d6 17ffff52 (e7f7defb)' | \
|
|
CROSS_COMPILE=aarch64-linux-gnu- ARCH=arm64 scripts/decodecode
|
|
Code: b00003c0 912ad000 940029d6 17ffff52 (e7f7defb)
|
|
All code
|
|
========
|
|
0: b00003c0 adrp x0, 0x79000
|
|
4: 912ad000 add x0, x0, #0xab4
|
|
8: 940029d6 bl 0xa760
|
|
c: 17ffff52 b 0xfffffffffffffd54
|
|
10:* e7f7defb .inst 0xe7f7defb ; undefined <-- trapping instruction
|
|
|
|
Code starting with the faulting instruction
|
|
===========================================
|
|
0: e7f7defb .inst 0xe7f7defb ; undefined
|
|
|
|
Now lets use the locations provided by the elr and lr registers after
|
|
subtracting the relocation offset to find out where in the code the crash
|
|
occurred and from where it was invoked.
|
|
|
|
File u-boot.map contains the memory layout of the U-Boot binary. Here we find
|
|
these lines::
|
|
|
|
.text.do_undefined
|
|
0x00000000000101fc 0xc cmd/built-in.o
|
|
.text.exception_complete
|
|
0x0000000000010208 0x90 cmd/built-in.o
|
|
...
|
|
.text.cmd_process
|
|
0x00000000000213b8 0x164 common/built-in.o
|
|
0x00000000000213b8 cmd_process
|
|
.text.cmd_process_error
|
|
0x000000000002151c 0x40 common/built-in.o
|
|
0x000000000002151c cmd_process_error
|
|
|
|
So the error occurred at the start of function do\_undefined() and this
|
|
function was invoked from somewhere inside function cmd\_process().
|
|
|
|
If we want to dive deeper, we can disassemble the U-Boot binary::
|
|
|
|
$ aarch64-linux-gnu-objdump -S -D u-boot | less
|
|
|
|
00000000000101fc <do_undefined>:
|
|
{
|
|
/*
|
|
* 0xe7f...f. is undefined in ARM mode
|
|
* 0xde.. is undefined in Thumb mode
|
|
*/
|
|
asm volatile (".word 0xe7f7defb\n");
|
|
101fc: e7f7defb .inst 0xe7f7defb ; undefined
|
|
return CMD_RET_FAILURE;
|
|
}
|
|
10200: 52800020 mov w0, #0x1 // #1
|
|
10204: d65f03c0 ret
|
|
|
|
This example is based on the ARMv8 architecture but the same procedures can be
|
|
used on other architectures as well.
|
|
|
|
Crashs in UEFI binaries
|
|
-----------------------
|
|
|
|
If UEFI images are loaded when a crash occurs, their load addresses are
|
|
displayed. If the process counter points to an address in a loaded UEFI
|
|
binary, the relative process counter position is indicated. Here is an
|
|
example executed on the U-Boot sandbox::
|
|
|
|
=> load host 0:1 $kernel_addr_r buggy.efi
|
|
5632 bytes read in 0 ms
|
|
=> bootefi $kernel_addr_r
|
|
Booting /buggy.efi
|
|
Buggy world!
|
|
|
|
Segmentation violation
|
|
pc = 0x19fc264c, pc_reloc = 0xffffaa4688b1664c
|
|
|
|
UEFI image [0x0000000019fc0000:0x0000000019fc6137] pc=0x264c '/buggy.efi'
|
|
|
|
The crash occured in UEFI binary buggy.efi at relative position 0x264c.
|
|
Disassembly may be used to find the actual source code location::
|
|
|
|
$ x86_64-linux-gnu-objdump -S -D buggy_efi.so
|
|
|
|
0000000000002640 <memset>:
|
|
2640: f3 0f 1e fa endbr64
|
|
2644: 48 89 f8 mov %rdi,%rax
|
|
2647: 48 89 f9 mov %rdi,%rcx
|
|
264a: eb 0b jmp 2657 <memset+0x17>
|
|
264c: 40 88 31 mov %sil,(%rcx)
|
|
|
|
Architecture specific details
|
|
-----------------------------
|
|
|
|
ARMv8
|
|
~~~~~
|
|
|
|
On the ARM 64-bit architecture CONFIG_ARMV8_SPL_EXCEPTION_VECTORS controls
|
|
if the exception vector tables are set up in the Secondary Program Loader (SPL).
|
|
Without initialization of the tables crash dumps cannot be shown. The feature is
|
|
disabled by default on most boards to reduce the size of the SPL.
|
|
|
|
RISC-V
|
|
~~~~~~
|
|
|
|
On the RISC-V architecture CONFIG_SHOW_REGS=y has to be specified to show
|
|
all registers in crash dumps.
|
|
|
|
Sandbox
|
|
~~~~~~~
|
|
|
|
The sandbox U-Boot binary must be invoked with parameter *-S* to display crash
|
|
dumps:
|
|
|
|
.. code-block:: bash
|
|
|
|
./u-boot -S -T
|
|
|
|
Only with CONFIG_SANDBOX_CRASH_RESET=y the sandbox reboots after a crash.
|