On Sun, 16 Mar 2025 at 00:18, Sam Edwards <cfswo...@gmail.com> wrote: > > LLVM's IAS does not (and cannot easily) support the 'adrl' > pseudoinstruction, and ARM developers generally do not consider it > portable across assembler implementations either. > > Instead, expand it into the two subtract instructions it would emit > anyway. An explanation of the math follows: > > The .+8 and .+4 refer to the same memory location; this is because the > .+4 expression occurs in a subsequent instruction, 4 bytes after the > first. This memory location is the value of the PC register when it is > read by the first sub instruction. Thus, both inner parenthesized > expressions evaluate to the same result: PC's offset relative to > image_base. The subtract instructions then remove one byte each > (low, then high) of the total offset, thereby getting the absolute > address of image_base loaded in r0. > > Signed-off-by: Sam Edwards <cfswo...@gmail.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodi...@linaro.org> > --- > arch/arm/lib/crt0_arm_efi.S | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/arm/lib/crt0_arm_efi.S b/arch/arm/lib/crt0_arm_efi.S > index 91b0fe12c51..235b3a0c48f 100644 > --- a/arch/arm/lib/crt0_arm_efi.S > +++ b/arch/arm/lib/crt0_arm_efi.S > @@ -149,7 +149,8 @@ _start: > adr r1, .L_DYNAMIC > ldr r0, [r1] > add r1, r0, r1 > - adrl r0, image_base > + sub r0, pc, #((.+8-image_base) & 0xff) > + sub r0, r0, #((.+4-image_base) & 0xff00) > bl _relocate > teq r0, #0 > bne 0f > -- > 2.48.1 >
