• Lukas Wunner's avatar
    x86/efi: Allow invocation of arbitrary boot services · 0a637ee6
    Lukas Wunner authored
    We currently allow invocation of 8 boot services with efi_call_early().
    Not included are LocateHandleBuffer and LocateProtocol in particular.
    For graphics output or to retrieve PCI ROMs and Apple device properties,
    we're thus forced to use the LocateHandle + AllocatePool + LocateHandle
    combo, which is cumbersome and needs more code.
    
    The ARM folks allow invocation of the full set of boot services but are
    restricted to our 8 boot services in functions shared across arches.
    
    Thus, rather than adding just LocateHandleBuffer and LocateProtocol to
    struct efi_config, let's rework efi_call_early() to allow invocation of
    arbitrary boot services by selecting the 64 bit vs 32 bit code path in
    the macro itself.
    
    When compiling for 32 bit or for 64 bit without mixed mode, the unused
    code path is optimized away and the binary code is the same as before.
    But on 64 bit with mixed mode enabled, this commit adds one compare
    instruction to each invocation of a boot service and, depending on the
    code path selected, two jump instructions. (Most of the time gcc
    arranges the jumps in the 32 bit code path.) The result is a minuscule
    performance penalty and the binary code becomes slightly larger and more
    difficult to read when disassembled. This isn't a hot path, so these
    drawbacks are arguably outweighed by the attainable simplification of
    the C code. We have some overhead anyway for thunking or conversion
    between calling conventions.
    
    The 8 boot services can consequently be removed from struct efi_config.
    
    No functional change intended (for now).
    
    Example -- invocation of free_pool before (64 bit code path):
    0x2d4      movq  %ds:efi_early, %rdx          ; efi_early
    0x2db      movq  %ss:arg_0-0x20(%rsp), %rsi
    0x2e0      xorl  %eax, %eax
    0x2e2      movq  %ds:0x28(%rdx), %rdi         ; efi_early->free_pool
    0x2e6      callq *%ds:0x58(%rdx)              ; efi_early->call()
    
    Example -- invocation of free_pool after (64 / 32 bit mixed code path):
    0x0dc      movq  %ds:efi_early, %rax          ; efi_early
    0x0e3      cmpb  $0, %ds:0x28(%rax)           ; !efi_early->is64 ?
    0x0e7      movq  %ds:0x20(%rax), %rdx         ; efi_early->call()
    0x0eb      movq  %ds:0x10(%rax), %rax         ; efi_early->boot_services
    0x0ef      je    $0x150
    0x0f1      movq  %ds:0x48(%rax), %rdi         ; free_pool (64 bit)
    0x0f5      xorl  %eax, %eax
    0x0f7      callq *%rdx
    ...
    0x150      movl  %ds:0x30(%rax), %edi         ; free_pool (32 bit)
    0x153      jmp   $0x0f5
    
    Size of eboot.o text section:
    CONFIG_X86_32:                         6464 before, 6318 after
    CONFIG_X86_64 && !CONFIG_EFI_MIXED:    7670 before, 7573 after
    CONFIG_X86_64 &&  CONFIG_EFI_MIXED:    7670 before, 8319 after
    Signed-off-by: default avatarLukas Wunner <lukas@wunner.de>
    Signed-off-by: default avatarMatt Fleming <matt@codeblueprint.co.uk>
    0a637ee6
eboot.c 28.8 KB