Dmesg not being dumped

[Nikolay Borisov]

On 08/19/2015 05:08 PM, Minfei Huang wrote:
> On 08/19/15 at 04:40pm, Nikolay Borisov wrote:
>> On 08/19/2015 04:13 PM, Minfei Huang wrote:
>>> Hi. Nikolay.
>>> Does kexec-tools work for original rhel kernel, like 3.10.0-xxx. Also do
>>
>> Unfortunately I canno test with an official rhel kernel since we are not
>> using those. Also, the problem is not that kexec is not working at all,
>> but just that the dmesg log is not being saved in the vmcore-dmesg.txt
>> file. Here are the relevant portion of the my .config which deal with
>> debug info:
>>
>> CONFIG_DEBUG_INFO=y
>> # CONFIG_DEBUG_INFO_REDUCED is not set
>> # CONFIG_DEBUG_INFO_SPLIT is not set
>> # CONFIG_DEBUG_INFO_DWARF4 is not set
> 
> I ran the kexec-tools-2.0.7-35 on kernel 4.2.0-rc5+ and kdump works
> successfully to dump the vmcore. The kernel is built by the default config
> (generated by make defconfig). Following is the relevant portions of the
> config. 
> 
>  # cat .config | grep KEXEC
> CONFIG_KEXEC=y
> CONFIG_KEXEC_FILE=y
> CONFIG_KEXEC_VERIFY_SIG=y
> CONFIG_KEXEC_BZIMAGE_VERIFY_SIG=y
> CONFIG_KEXEC_JUMP=y
>  # cat .config | grep DEBUG_INFO
> CONFIG_DEBUG_INFO=y
> # CONFIG_DEBUG_INFO_REDUCED is not set
> # CONFIG_DEBUG_INFO_SPLIT is not set
> # CONFIG_DEBUG_INFO_DWARF4 is not set
> 
> Thanks
> Minfei

I only have CONFIG_KEXEC=y but the others are not necessary as far as I
can tell. I don't do any verification  so the VERIFY_SIG are disabled.
KEXEC_JUMP is also n, since I haven't enabled hibernation and KEXEC_FILE
is also not critical.  My debug info is the same as yours.


> 
>>
>> The failures is happening (according to my reading of the vmcore-dmesg.c
>> file) here:
>>
>> +	if (!log_sz) {
>> +		fprintf(stderr, "Missing the struct log size export\n");
>> +		exit(64);
>> +	}
>>
>> And log_size is being set here:
>>
>> 		str = "SIZE(printk_log)=";
>> 		if (memcmp(str, pos, strlen(str)) == 0)
>> 			log_sz = strtoull(pos + strlen(str), NULL, 10);
>>
>> The pertinent question I guess is why this string cannot be found in the
>> resulting vmcore image. I just tried with kexec 2.0.10 and the result is
>> the same.