On 15 July 2014 11:57, Mark Rutland <mark.rutland@xxxxxxx> wrote: > Hi Ard, > > On Tue, Jul 15, 2014 at 10:10:02AM +0100, Ard Biesheuvel wrote: >> After the EFI stub has done its business, it jumps into the kernel by branching >> to offset #0 of the loaded Image, which is where it expects to find the header >> containing a 'branch to stext' instruction. >> However, the header is not covered by any PE/COFF section, so the header may >> not actually be loaded at the expected offset. So instead, jump to 'stext' >> directly, which is at the base of the PE/COFF .text section. > > It would be nice to point out in the commit message that the other > changes in the patch are just cleanup to use stext_offset rather than > open-coding it. > OK >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> >> --- >> arch/arm64/kernel/efi-entry.S | 2 +- >> arch/arm64/kernel/head.S | 10 ++++++---- >> 2 files changed, 7 insertions(+), 5 deletions(-) >> >> diff --git a/arch/arm64/kernel/efi-entry.S b/arch/arm64/kernel/efi-entry.S >> index 619b1dd7bcde..6ef541731d9e 100644 >> --- a/arch/arm64/kernel/efi-entry.S >> +++ b/arch/arm64/kernel/efi-entry.S >> @@ -61,7 +61,7 @@ ENTRY(efi_stub_entry) >> */ >> mov x20, x0 // DTB address >> ldr x0, [sp, #16] // relocated _text address >> - mov x21, x0 >> + add x21, x0, #:lo12:stext_offset > > I think we can drop the :lo12: here, which will allow us to have a > warning if stext_offset is unexpectedly large (I believe this will > currently silently mask bits were that to happen?). > There is no alternative lo12 relocation that errors out when the value does not fit, so it would have to use a literal instead. > Other than that, this looks like a sensible thing to do given that we > cannot rely on the header being present. > Cheers, Ard. >> >> /* >> * Flush dcache covering current runtime addresses >> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S >> index a2c1195abb7f..78ddae28b090 100644 >> --- a/arch/arm64/kernel/head.S >> +++ b/arch/arm64/kernel/head.S >> @@ -137,6 +137,8 @@ efi_head: >> #endif >> >> #ifdef CONFIG_EFI >> + .globl stext_offset >> + .set stext_offset, stext - efi_head >> .align 3 >> pe_header: >> .ascii "PE" >> @@ -160,7 +162,7 @@ optional_header: >> .long 0 // SizeOfInitializedData >> .long 0 // SizeOfUninitializedData >> .long efi_stub_entry - efi_head // AddressOfEntryPoint >> - .long stext - efi_head // BaseOfCode >> + .long stext_offset // BaseOfCode >> >> extra_header_fields: >> .quad 0 // ImageBase >> @@ -177,7 +179,7 @@ extra_header_fields: >> .long _edata - efi_head // SizeOfImage >> >> // Everything before the kernel image is considered part of the header >> - .long stext - efi_head // SizeOfHeaders >> + .long stext_offset // SizeOfHeaders >> .long 0 // CheckSum >> .short 0xa // Subsystem (EFI application) >> .short 0 // DllCharacteristics >> @@ -222,9 +224,9 @@ section_table: >> .byte 0 >> .byte 0 // end of 0 padding of section name >> .long _edata - stext // VirtualSize >> - .long stext - efi_head // VirtualAddress >> + .long stext_offset // VirtualAddress >> .long _edata - stext // SizeOfRawData >> - .long stext - efi_head // PointerToRawData >> + .long stext_offset // PointerToRawData >> >> .long 0 // PointerToRelocations (0 for executables) >> .long 0 // PointerToLineNumbers (0 for executables) >> -- >> 1.8.3.2 >> >> -- 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
