On Mon, 22 Aug, at 12:01:21PM, Lukas Wunner wrote: > 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: Lukas Wunner <lukas@xxxxxxxxx> > Cc: Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx> > --- > arch/x86/boot/compressed/eboot.c | 13 +------------ > arch/x86/boot/compressed/head_32.S | 6 +++--- > arch/x86/boot/compressed/head_64.S | 8 ++++---- > arch/x86/include/asm/efi.h | 15 ++++++--------- > 4 files changed, 14 insertions(+), 28 deletions(-) Nice, I like this. Applied pending the update to the first patch. -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
