[efi] Add support for executing images via a shim

Add support for using a shim as a helper to execute an EFI image.
When a shim has been specified via shim(), the shim image will be
passed to LoadImage() instead of the selected EFI image, the command
line will be prepended with the name of the selected EFI image, and
the selected EFI image will be exposed via the virtual filesystem as
the fixed second stage file.

Construct the default second stage alternative filename based on the
EFI removable media filename, since that matches the pattern used by
shim for all currently supported architectures.

Do not install the EFI PXE APIs when using a shim, since if shim finds
EFI_PXE_BASE_CODE_PROTOCOL on the loaded image's device handle then it
will attempt to download files afresh instead of using the files
already downloaded by iPXE and exposed via the EFI_SIMPLE_FILE_SYSTEM
protocol.  (Experience shows that there is no point in trying to get a
fix for this upstreamed into shim.)

Signed-off-by: Michael Brown <mcb30@ipxe.org>

0 files changed, 0 insertions, 0 deletions