On Tue, Jul 15, 2014 at 12:49:07PM +0100, Ard Biesheuvel wrote: > On 15 July 2014 13:31, Mark Rutland <mark.rutland@xxxxxxx> wrote: > >> >> 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. > > > > Ah, that's a shame. What happens when the value doesn't fit if the > > linker / assembler don't error out? > > > > Obviously, it will jump into the wrong place if stext ever gets pushed > beyond a 4k boundary, which is not that likely (current value is > 0x160, we may want to up it to 0x200 at some point if we need to > increase the PE/COFF section alignment, which some versions of the > (poor) PE/COFF documentation say should be 0x200 at the minimum) > > However, doing ldr x21, =stext_offset works fine as well > > > That sounds like a toolchain bug if they're silently doing the wrong > > thing. > > > > Meh, don't think so, really. You get what you pay for, and :lo12: just > isn't supposed to care. (It's mainly used with adrp to get a +/- 4gb > PC relative reach) We appear to have a misunderstanding. I was suggesting we use: add x21, x0, #stext_offset ... and I thought you meant that wouldn't produce an error if the immediate was out of range. I understand that :lo12: cuts the top bits off, and for its intended use that makes sense. >From testing I see see that gas isn't happy to accept an undefined symbol as an immediate without :lo12:, and I can see why that makes sense. My suggestion was bad, sorry. Thanks, Mark. -- 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
