kexec'd kernel fails to locate RSDP on an EFI system

[vcaputo]

Others have experienced similar issues surrounding kdump on efi systems:
http://lists.infradead.org/pipermail/kexec/2012-October/006924.html
http://lists.infradead.org/pipermail/kexec/2010-March/003889.html

A simple solution seems to be adding the following to the kernel cmdline supplied via kexec in bootengine on efi systems:

acpi_rsdp=$(grep -m1 ^ACPI /sys/firmware/efi/systab | cut -f2- -d=)

[vcaputo]

@brianredbeard was able to get his efi sbc to boot coreos via bootengine successfully by manually placing the acpi_rsdp= field in the syslinux/boot_kernel.cfg which propagated down to the bootengine kexec thanks to the --reuse-cmdline.

[nh2]

Note that this also helps when you're running a kernel started via kexec and poweroff does not work, and dmesg prints and hangs at:

reboot: System halted

Passing the mentioned kernel parameter during the kexec invocation allows the kexec'ed kernel to poweroff in that case.

[nh2]

While the above is a workaround, I have now identified two bugs in kexec that made it necessary in my case, and proposed patches to fix them at http://lists.infradead.org/pipermail/kexec/2019-April/022964.html