where/how 2nd kernel's elfcorehdr_addr comes from

where/how 2nd kernel's elfcorehdr_addr comes from

[lizhijian]

Hi folks,

I'm trying to add pmem's metadata(located at pmem device) to 
/proc/vmcore. To accomplish this, I think

something i need to know is where the contents of /proc/vmcore come 
from, and then append

something into it.

I have read 
https://opensource.com/article/17/6/kdump-usage-and-internals, and knew 
/proc/vmcore is a elf file.

It mentioned that "Creates /proc/vmcore as per elfcorehdr information 
received", but i don't get how it

elfcorehdr(maybe elfcorehdr_addr) be assigned in 2nd kernel.

I tried to grep it in the kernel source, but still no answer.  So i deep 
hope you guys can give me some hints or answer.

and thank you in advance :)

[root@iaas-rpma linux]# git grep elfcorehdr_addr | grep -v -w -e ia64 -e 
loongarch -e mips -e powerpc  -e riscv

arch/s390/kernel/setup.c:       elfcorehdr_addr = ELFCORE_ADDR_MAX;

drivers/of/fdt.c:       if (memblock_is_region_reserved(elfcorehdr_addr, 
elfcorehdr_size)) {

drivers/of/fdt.c:       memblock_reserve(elfcorehdr_addr, elfcorehdr_size);

drivers/of/fdt.c:               elfcorehdr_size >> 10, elfcorehdr_addr);

drivers/of/fdt.c:       elfcorehdr_addr = 
dt_mem_next_cell(dt_root_addr_cells, &prop);

drivers/of/fdt.c:                elfcorehdr_addr, elfcorehdr_size);

fs/proc/vmcore.c:       addr = elfcorehdr_addr;

fs/proc/vmcore.c:       addr = elfcorehdr_addr;

fs/proc/vmcore.c:       addr = elfcorehdr_addr;

fs/proc/vmcore.c:       addr = elfcorehdr_addr;

fs/proc/vmcore.c:       addr = elfcorehdr_addr;

fs/proc/vmcore.c:       rc = elfcorehdr_alloc(&elfcorehdr_addr, 
&elfcorehdr_size);

fs/proc/vmcore.c:       elfcorehdr_free(elfcorehdr_addr);

fs/proc/vmcore.c:       elfcorehdr_addr = ELFCORE_ADDR_ERR;

include/linux/crash_dump.h:extern unsigned long long elfcorehdr_addr;

include/linux/crash_dump.h:     return elfcorehdr_addr != ELFCORE_ADDR_MAX;

include/linux/crash_dump.h:     return is_kdump_kernel() && 
elfcorehdr_addr != ELFCORE_ADDR_ERR ? 1 : 0;

include/linux/crash_dump.h:             elfcorehdr_addr = ELFCORE_ADDR_ERR;

kernel/crash_dump.c: * Note: elfcorehdr_addr is not just limited to 
vmcore. It is also used by

kernel/crash_dump.c:unsigned long long elfcorehdr_addr = ELFCORE_ADDR_MAX;

kernel/crash_dump.c:EXPORT_SYMBOL_GPL(elfcorehdr_addr);

kernel/crash_dump.c:    elfcorehdr_addr = memparse(arg, &end);

kernel/crash_dump.c:            elfcorehdr_size = elfcorehdr_addr;

kernel/crash_dump.c:            elfcorehdr_addr = memparse(end + 1, &end);

Thanks

Zhijian
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Re: where/how 2nd kernel's elfcorehdr_addr comes from

[lizhijian]

On 04/11/2022 17:03, Li, Zhijian/李 智坚 wrote:
> Hi folks,
>
> I'm trying to add pmem's metadata(located at pmem device) to
> /proc/vmcore. To accomplish this, I think
>
> something i need to know is where the contents of /proc/vmcore come
> from, and then append
>
> something into it.
>
> I have read
> https://opensource.com/article/17/6/kdump-usage-and-internals, and knew
> /proc/vmcore is a elf file.
>
> It mentioned that "Creates /proc/vmcore as per elfcorehdr information
> received", but i don't get how it
>
> elfcorehdr(maybe elfcorehdr_addr) be assigned in 2nd kernel.

I got it, elfcorehdr comes from 1st kernel's kexec-tools which passes 
elfcorehdr=xxx to 2nd kernel

Thanks


>
> I tried to grep it in the kernel source, but still no answer.  So i deep
> hope you guys can give me some hints or answer.
>
> and thank you in advance :)
>
> [root@iaas-rpma linux]# git grep elfcorehdr_addr | grep -v -w -e ia64 -e
> loongarch -e mips -e powerpc  -e riscv
>
> arch/s390/kernel/setup.c:       elfcorehdr_addr = ELFCORE_ADDR_MAX;
>
> drivers/of/fdt.c:       if (memblock_is_region_reserved(elfcorehdr_addr,
> elfcorehdr_size)) {
>
> drivers/of/fdt.c:       memblock_reserve(elfcorehdr_addr, elfcorehdr_size);
>
> drivers/of/fdt.c:               elfcorehdr_size >> 10, elfcorehdr_addr);
>
> drivers/of/fdt.c:       elfcorehdr_addr =
> dt_mem_next_cell(dt_root_addr_cells, &prop);
>
> drivers/of/fdt.c:                elfcorehdr_addr, elfcorehdr_size);
>
> fs/proc/vmcore.c:       addr = elfcorehdr_addr;
>
> fs/proc/vmcore.c:       addr = elfcorehdr_addr;
>
> fs/proc/vmcore.c:       addr = elfcorehdr_addr;
>
> fs/proc/vmcore.c:       addr = elfcorehdr_addr;
>
> fs/proc/vmcore.c:       addr = elfcorehdr_addr;
>
> fs/proc/vmcore.c:       rc = elfcorehdr_alloc(&elfcorehdr_addr,
> &elfcorehdr_size);
>
> fs/proc/vmcore.c:       elfcorehdr_free(elfcorehdr_addr);
>
> fs/proc/vmcore.c:       elfcorehdr_addr = ELFCORE_ADDR_ERR;
>
> include/linux/crash_dump.h:extern unsigned long long elfcorehdr_addr;
>
> include/linux/crash_dump.h:     return elfcorehdr_addr != ELFCORE_ADDR_MAX;
>
> include/linux/crash_dump.h:     return is_kdump_kernel() &&
> elfcorehdr_addr != ELFCORE_ADDR_ERR ? 1 : 0;
>
> include/linux/crash_dump.h:             elfcorehdr_addr = ELFCORE_ADDR_ERR;
>
> kernel/crash_dump.c: * Note: elfcorehdr_addr is not just limited to
> vmcore. It is also used by
>
> kernel/crash_dump.c:unsigned long long elfcorehdr_addr = ELFCORE_ADDR_MAX;
>
> kernel/crash_dump.c:EXPORT_SYMBOL_GPL(elfcorehdr_addr);
>
> kernel/crash_dump.c:    elfcorehdr_addr = memparse(arg, &end);
>
> kernel/crash_dump.c:            elfcorehdr_size = elfcorehdr_addr;
>
> kernel/crash_dump.c:            elfcorehdr_addr = memparse(end + 1, &end);
>
> Thanks
>
> Zhijian
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Re: where/how 2nd kernel's elfcorehdr_addr comes from

[Baoquan He]

On 11/04/22 at 09:03am, lizhijian@fujitsu.com wrote:
> Hi folks,
> 
> I'm trying to add pmem's metadata(located at pmem device) to 
> /proc/vmcore. To accomplish this, I think
> 
> something i need to know is where the contents of /proc/vmcore come 
> from, and then append
> 
> something into it.
> 
> I have read 
> https://opensource.com/article/17/6/kdump-usage-and-internals, and knew 
> /proc/vmcore is a elf file.
> 
> It mentioned that "Creates /proc/vmcore as per elfcorehdr information 
> received", but i don't get how it
> 
> elfcorehdr(maybe elfcorehdr_addr) be assigned in 2nd kernel.
> 
> I tried to grep it in the kernel source, but still no answer.  So i deep 
> hope you guys can give me some hints or answer.

Since you have studied this, so:
crash_prepare_elf64_headers() is the place where elf header of vmcore is
contructed in 1st kernel. And in crash_load_segments() it's prepared to
be passed out. I am talking about x86, and kexec_file load. You should
be able to find the similar thing in user space code.


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