Installing shim-signed:amd64 is met with a "cat: /sys/firmware/efi/fw_platform_size: No such file or directory" error

[Derrick Karpo <dkarpo@gmail.com>]

Hello.

I'm using live-build 1:20210407 and on Friday the build worked fine
but today during the build it errored. Note: This may be a shim-signed
issue and not a live-build issue!

<snip>
Setting up shim-signed:amd64 (1.34+15.4-2) ...
cat: /sys/firmware/efi/fw_platform_size: No such file or directory
dpkg: error processing package shim-signed:amd64 (--configure):
 installed shim-signed:amd64 package post-installation script
subprocess returned error exit status 1
Errors were encountered while processing:
 shim-signed:amd64
E: Sub-process /usr/bin/dpkg returned an error code (1)
Setting up shim-signed:amd64 (1.34+15.4-2) ...
cat: /sys/firmware/efi/fw_platform_size: No such file or directory
dpkg: error processing package shim-signed:amd64 (--configure):
 installed shim-signed:amd64 package post-installation script
subprocess returned error exit status 1
Errors were encountered while processing:
 shim-signed:amd64
<snip>

I went into the chroot and when manually installing shim-signed it
still fails. I bind mounted /sys and /dev and the failures still
happen in that it "cat: /sys/firmware/efi/fw_platform_size: No such
file or directory".

<snip>
# apt-get install shim-signed:amd64
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
shim-signed is already the newest version (1.34+15.4-2).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
1 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n]
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
        LANGUAGE = "en_CA:en",
        LC_ALL = (unset),
        LANG = "en_CA.UTF-8"
    are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").
E: Can not write log (Is /dev/pts mounted?) - posix_openpt (19: No such device)
Setting up shim-signed:amd64 (1.34+15.4-2) ...
cat: /sys/firmware/efi/fw_platform_size: No such file or directory
<snip>

Yesterday there was an update to shim-signed in Debian sid and my
suspicion is that it is the cause for the error as nothing else has
really changed in this build environment. I'm just not sure if this
should be reported as a live-build issue or a shim-signed issue?
Perhaps it's a user issue and I'm missing something to expose the UEFI
firmware bitness via sysfs? Any assistance you can provide would be
appreciated!

Derrick