new version of shim refuses to chainload windows in dualboot

[gueba]

[Impact]
Dual-boot installs of Ubuntu and Windows 10, and other instances of chainloading another bootloader from grub2.

[Test cases]
1) Install Windows 10
2) Install Ubuntu in a dual-boot setup with the existing Windows 10 install. (resize or install on a second disk)
3) Boot to the "ubuntu" entry in UEFI firmware.
4) Hold Shift to get the grub menu
5) Pick "Windows 10" at the grub menu

Verify that the Windows 10 entry from grub menu correctly boots to Windows 10. Without the patch, there should be a "relocation failed" error message. With the patch, Windows 10 should start normally.

[Regression potential]
Regressions would show up as other cases of failure to load the bootloader that is being chainloaded to -- it is not noticeably different than the current failure more (which is also a failure to load the bootloader). Chainload is otherwise unlikely to affect the started loader.

---

package: shim-signed, shim

release: Ubuntu 18.04.1 LTS

version: shim-signed:amd64 1.37~18.04.1+15+1533136590.3beb971-0ubuntu1
 shim:amd64 15+1533136590.3beb971-0ubuntu1

expected: grub menu loading xubuntu and windows in dualboot

happened: loading xubuntu works, loading windows failes (no error - black screen - no hard disc light flashing)
I uninstalled shim, shim-signed, disabled 'bionic-updates' and installed old versions
shim-signed:amd64 1.34.9.2+13-0ubuntu2
shim:amd64 13-0ubuntu2
and boot works well like before.

I enabled 'bionic-updates' and installed the newer versions without error and again chainloading of windows fails.

[Mathieu Trudel-Lapierre (cyphermox)]

We rolled back shim; this would now be regression-proposed.

[Mathieu Trudel-Lapierre (cyphermox)]

This is identified as a proper "typo" bug in grub, fixing.