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authorMatt Fleming <matt.fleming@intel.com>2014-01-10 15:54:31 +0000
committerMatt Fleming <matt.fleming@intel.com>2014-03-04 21:25:06 +0000
commitb8ff87a6158886771677e6dc8139bac6e3cba717 (patch)
treec781f609a9949236ae88a302d330e5d319ea9e1a /arch/x86/include/asm/efi.h
parentc116e8d60adabfd545a269fccab85e77febc1643 (diff)
downloadop-kernel-dev-b8ff87a6158886771677e6dc8139bac6e3cba717.zip
op-kernel-dev-b8ff87a6158886771677e6dc8139bac6e3cba717.tar.gz
x86/efi: Firmware agnostic handover entry points
The EFI handover code only works if the "bitness" of the firmware and the kernel match, i.e. 64-bit firmware and 64-bit kernel - it is not possible to mix the two. This goes against the tradition that a 32-bit kernel can be loaded on a 64-bit BIOS platform without having to do anything special in the boot loader. Linux distributions, for one thing, regularly run only 32-bit kernels on their live media. Despite having only one 'handover_offset' field in the kernel header, EFI boot loaders use two separate entry points to enter the kernel based on the architecture the boot loader was compiled for, (1) 32-bit loader: handover_offset (2) 64-bit loader: handover_offset + 512 Since we already have two entry points, we can leverage them to infer the bitness of the firmware we're running on, without requiring any boot loader modifications, by making (1) and (2) valid entry points for both CONFIG_X86_32 and CONFIG_X86_64 kernels. To be clear, a 32-bit boot loader will always use (1) and a 64-bit boot loader will always use (2). It's just that, if a single kernel image supports (1) and (2) that image can be used with both 32-bit and 64-bit boot loaders, and hence both 32-bit and 64-bit EFI. (1) and (2) must be 512 bytes apart at all times, but that is already part of the boot ABI and we could never change that delta without breaking existing boot loaders anyhow. Signed-off-by: Matt Fleming <matt.fleming@intel.com>
Diffstat (limited to 'arch/x86/include/asm/efi.h')
-rw-r--r--arch/x86/include/asm/efi.h6
1 files changed, 3 insertions, 3 deletions
diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
index 3d6b9f8..8585686 100644
--- a/arch/x86/include/asm/efi.h
+++ b/arch/x86/include/asm/efi.h
@@ -19,9 +19,11 @@
*/
#define EFI_OLD_MEMMAP EFI_ARCH_1
+#define EFI32_LOADER_SIGNATURE "EL32"
+#define EFI64_LOADER_SIGNATURE "EL64"
+
#ifdef CONFIG_X86_32
-#define EFI_LOADER_SIGNATURE "EL32"
extern unsigned long asmlinkage efi_call_phys(void *, ...);
@@ -57,8 +59,6 @@ extern unsigned long asmlinkage efi_call_phys(void *, ...);
#else /* !CONFIG_X86_32 */
-#define EFI_LOADER_SIGNATURE "EL64"
-
extern u64 efi_call0(void *fp);
extern u64 efi_call1(void *fp, u64 arg1);
extern u64 efi_call2(void *fp, u64 arg1, u64 arg2);
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