efi/libstub: Output UTF-16 directly from vsnprintf()

The only remaining users of vsnprintf() in the EFI stub are the
diagnostic printk()'s, which are emitted to the console and not recorded
for posterity.

The EFI console uses UTF-16 (or actually, UCS-2) natively, and so all
non-UTF16 strings that are emitted need to be converted. Given the
stub's vsnprintf() support for wide strings (using the %ls conversion
modifier), which uses UTF-16 to UTF-8 conversion internally, the final
conversion to UTF-16 needs to support not just plain ASCII but UTF-8 as
well.

This is all pointless, of course, and it makes more sense to use UTF-16
internally. This removes the need for UTF-16 to UTF-8 conversion in
vsnprintf(), and given that all non-wide string inputs to vsnprintf()
that exist in the stub today are compile time constant ASCII strings,
the need to convert UTF-8 to UTF-16 disappears as well.

So implement efi_vsnprintf() taking a const char *fmt as before, but
outputting a efi_char16_t[] that can be passed to the EFI console
directly, rather than via efi_puts(), leaving the latter unused and
therefore removed.

Note that efi_puts() performs LF to CR-LF conversion internally, so add
this capability to efi_vsnprintf() as well.

Reviewed-by: Vincent Mailhol <mailhol@kernel.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

0 files changed, 0 insertions, 0 deletions