Kernel Crash Dump (kdump) broken with 6.5

[Mahesh J Salgaonkar]

On 2023-07-17 20:15:53 Mon, Sachin Sant wrote:
> Kdump seems to be broken with 6.5 for ppc64le.
> 
> [ 14.200412] systemd[1]: Starting dracut pre-pivot and cleanup hook...
> [[0;32m OK [0m] Started dracut pre-pivot and cleanup hook.
> Starting Kdump Vmcore Save Service...
> [ 14.231669] systemd[1]: Started dracut pre-pivot and cleanup hook.
> [ 14.231801] systemd[1]: Starting Kdump Vmcore Save Service...
> [ 14.341035] kdump.sh[297]: kdump: saving to /sysroot//var/crash//127.0.0.1-2023-07-14-13:32:34/
> [ 14.350053] EXT4-fs (sda2): re-mounted e971a335-1ef8-4295-ab4e-3940f28e53fc r/w. Quota mode: none.
> [ 14.345979] kdump.sh[297]: kdump: saving vmcore-dmesg.txt to /sysroot//var/crash//127.0.0.1-2023-07-14-13:32:34/
> [ 14.348742] kdump.sh[331]: Cannot open /proc/vmcore: No such file or directory
> [ 14.348845] kdump.sh[297]: kdump: saving vmcore-dmesg.txt failed
> [ 14.349014] kdump.sh[297]: kdump: saving vmcore
> [ 14.443422] kdump.sh[332]: open_dump_memory: Can't open the dump memory(/proc/vmcore). No such file or directory
> [ 14.456413] kdump.sh[332]: makedumpfile Failed.
> [ 14.456662] kdump.sh[297]: kdump: saving vmcore failed, _exitcode:1
> [ 14.456822] kdump.sh[297]: kdump: saving the /run/initramfs/kexec-dmesg.log to /sysroot//var/crash//127.0.0.1-2023-07-14-13:32:34/
> [ 14.487002] kdump.sh[297]: kdump: saving vmcore failed
> [[0;1;31mFAILED[0m] Failed to start Kdump Vmcore Save Service.

Thanks Sachin for catching this.

> 
> 6.4 was good. Git bisect points to following patch
> 
> commit 606787fed7268feb256957872586370b56af697a
>     powerpc/64s: Remove support for ELFv1 little endian userspace
> 
> Reverting this patch allows a successful capture of vmcore.
> 
> Does this change require any corresponding change to kdump
> and/or kexec tools?

Need to investigate that. It looks like vmcore_elf64_check_arch(&ehdr)
check from fs/proc/vmcore.c is failing after above commit.

static int __init parse_crash_elf64_headers(void)
{
[...]

        /* Do some basic Verification. */
        if (memcmp(ehdr.e_ident, ELFMAG, SELFMAG) != 0 ||
                (ehdr.e_type != ET_CORE) ||
                !vmcore_elf64_check_arch(&ehdr) ||
[...]

It looks like ehdr->e_flags are not set properly while generating vmcore
ELF header. I see that in kexec_file_load, ehdr->e_flags left set to 0
irrespective of IS_ENABLED(CONFIG_PPC64_ELF_ABI_V2) is true or false.

-Mahesh