On x86_64 without HAVE_USE_MS_ABI support, uefi_call_wrapper() is a
variadic function. Parameters >=5 are copied to the stack and, when
passed small immediate values (and possibly other parameters), gcc
would emit a movl instruction before calling uefi_call_wrapper(). As a
result, only the lower 32b of these stack values are significant, the
upper 32b potentially contain garbage. Considering that
uefi_call_wrapper() assumes these arguments are clean 64b values
before calling the efi_callX() trampolines, the latter may be passed
garbage. This makes calling functions like
EFI_PCI_IO_PROTOCOL.Mem.Read()/Write() or BS->OpenProtocol() quite
unreliable.
This patch fixes this by turning uefi_call_wrapper() into a macro that
allows to expose the efi_callX() trampoline signatures to the callers,
so that gcc can know upfront that it has to pass all arguments to
efi_callX() as clean 64b values (eg. movq for immediates). The
_cast64_efi_callX macros are just here to avoid a gcc warning, they do
nothing otherwise.
Signed-off-by: David Decotigny <decot@googlers.com>
c0b8d974a6