pstore -last kmsg

To enable it, take the below step (test on MSM8916)

enable below config in kernel config:

```

CONFIG_PSTORE=y

CONFIG_PSTORE_CONSOLE=y

CONFIG_PSTORE_RAM=y

CONFIG_PSTORE_FTRACE=y

CONFIG_PSTORE_PMSG=y

CONFIG_DEBUG_FS=y

CONFIG_FUNCTION_TRACER=y

```

and disable below config:

# CONFIG_STRICT_MEMORY_RWX

-----code changes ------

LINUX/android/kernel/fs/pstore/ram.c

```

-static ulong ramoops_console_size = MIN_MEM_SIZE;

+static ulong ramoops_console_size = 256*1024UL;

- static ulong mem_address;

+ static ulong mem_address=0x9ff00000;

module_param(mem_address, ulong, 0400);

MODULE_PARM_DESC(mem_address,  "start of reserved RAM used to store oops/panic logs");

- static ulong mem_size;

+ static ulong mem_size=0x100000;

```

kernel/arch/arm/boot/dts/qcom/msm8916-memory.dtsi

```   

    peripheral_mem: pheripheral_region@0 {

            linux,reserve-contiguous-region;

            linux,reserve-region;

            linux,remove-completely;

            reg = <0x0 0x8b600000 0x0 0x0600000>;

            label = "peripheral_mem";

        };

+        pstore_reserve_mem: pstore_reserve_mem_region@0 {

+            linux,reserve-contiguous-region;

+            linux,reserve-region;

+            linux,remove-completely;

+            reg = <0x0 0x9ff00000 0x0 0x00100000>;

+            label = "pstore_reserve_mem";

+        };

```

-----test command ------

enable record ftrace

```

# mount -t debugfs debugfs /sys/kernel/debug/

# echo 1 > /sys/kernel/debug/pstore/record_ftrace

disable download mode:

# echo 0 > /sys/module/msm_poweroff/parameters/download_mode

# echo c > /proc/sysrq-trigger

```

[...device restart]

```

# ls /sys/fs/pstore/

  console-ramoops

  dmesg-ramoops-0

  dmesg-ramoops-1

  ftrace-ramoops

# cat /sys/fs/pstore/ftrace-ramoops

0 c08bf830  c08bfbf0  do_page_fault.part.8 <- do_page_fault+0x3c/0xa8

0 c001b770  c08bfb48  fixup_exception <- do_page_fault.part.8+0x32c/0x398

0 c0045bb0  c001b780  search_exception_tables <- fixup_exception+0x20/0x38

0 c008914c  c0045bd8  search_module_extables <- search_exception_tables+0x38/0x44

0 c08bff5c  c008915c  add_preempt_count <- search_module_extables+0x24/0xc0

0 c08bfe78  c00891cc  sub_preempt_count <- search_module_extables+0x94/0xc0

0 c08b2e28  c08bfb64  __do_kernel_fault.part.7 <- do_page_fault.part.8+0x348/0x398

```

--------------------------------------------------------

workaround for 8916/39/94 64 bit version:

ram_core.c (kernel\fs\pstore)  

```

+static void *memcpy_pstore(void *dest, const void *src, size_t count)

+{

+    char *tmp = dest;

+    const char *s = src;

+

+    while (count--)

+        *tmp++ = *s++;

+    return dest;

+}

static void notrace persistent_ram_update(struct persistent_ram_zone *prz,

    const void *s, unsigned int start, unsigned int count)

{

    struct persistent_ram_buffer *buffer = prz->buffer;

-    memcpy(buffer->data + start, s, count);

+    memcpy_pstore(buffer->data + start, s, count);

    persistent_ram_update_ecc(prz, start, count);

}

```

# 立即重新启动计算机

echo b > /proc/sysrq-trigger

# 立即关闭计算机

echo o > /proc/sysrq-trigger

# 导出内存分配的信息 （可以用/var/log/message 查看）

echo m > /proc/sysrq-trigger

# 导出当前CPU寄存器信息和标志位的信息

echo p > /proc/sysrq-trigger

# 导出线程状态信息

echo t > /proc/sysrq-trigger

# 故意让系统崩溃

echo c > /proc/sysrq-trigger

# 立即重新挂载所有的文件系统

echo s > /proc/sysrq-trigger

# 立即重新挂载所有的文件系统为只读

echo u > /proc/sysrq-trigger

备注： 上面的patch重点是找到一个地址，作为resvered 0x1000000开始地址

// user 版本有问题

pstore 有没有build  check .config

如果不能保存pstore,需要check 是否是warm reboot 还是cold reboot

echo 1 /sys/module/msm_poweroff/parameters/download_mode

bool need_warm_reset = true;

in_panic=1---> 会进入download mode, 如果设定成0 ， 则download ->reboot,