On 10 October 2014 12:33, Mark Rutland <mark.rutland@xxxxxxx> wrote: > Hi Ard, > > On Fri, Oct 10, 2014 at 10:25:24AM +0100, Ard Biesheuvel wrote: >> Position independent AArch64 code needs to be linked and loaded at the same >> relative offset from a 4 KB boundary, or adrp/add and adrp/ldr pairs will >> not work correctly. (This is how PC relative symbol references with a 4 GB >> reach are emitted) >> >> We need to declare this in the PE/COFF header, otherwise the PE/COFF loader >> may load the Image and invoke the stub at an offset which violates this rule. > > Has this been observed happening, or was this just found by inspection? > This is also something found by inspection, or rather, by the discussion going on in the other thread. I am not aware of any PE/COFF loaders that may choose an offset that is not 4 KB aligned, even if the header we give it appears to allow it. >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> >> --- >> arch/arm64/kernel/head.S | 4 ++-- >> 1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S >> index 0a6e4f924df8..5e83e5b8a9de 100644 >> --- a/arch/arm64/kernel/head.S >> +++ b/arch/arm64/kernel/head.S >> @@ -159,7 +159,7 @@ optional_header: >> >> extra_header_fields: >> .quad 0 // ImageBase >> - .long 0x20 // SectionAlignment >> + .long 0x1000 // SectionAlignment >> .long 0x8 // FileAlignment >> .short 0 // MajorOperatingSystemVersion >> .short 0 // MinorOperatingSystemVersion >> @@ -226,7 +226,7 @@ section_table: >> .short 0 // NumberOfRelocations (0 for executables) >> .short 0 // NumberOfLineNumbers (0 for executables) >> .long 0xe0500020 // Characteristics (section flags) >> - .align 5 >> + .align 12 > > Can we get a comment explaining why stext needs the additional > alignment? Something like: > > /* > * EFI will load stext onwards at the 4k section alignment > * described in the PE/COFF header. To ensure that instruction > * sequences using an adrp and a :lo12: immediate will function > * correctly at this alignment, we must ensure that stext is > * placed at a 4k boundary in the Image to begin with. > */ > .align 12 > OK -- Ard. -- 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
