On Thu, Aug 18, 2016 at 02:10:29PM +0100, Suzuki K Poulose wrote: > adrp uses PC-relative address offset to a page (of 4K size) of > a symbol. If it appears in an alternative code patched in, we > should adjust the offset to reflect the address where it will > be run from. This patch adds support for fixing the offset > for adrp instructions. > > Cc: Will Deacon <[email protected]> > Cc: Marc Zyngier <[email protected]> > Cc: Andre Przywara <[email protected]> > Cc: Mark Rutland <[email protected]> > Signed-off-by: Suzuki K Poulose <[email protected]> > --- > arch/arm64/kernel/alternative.c | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/arch/arm64/kernel/alternative.c b/arch/arm64/kernel/alternative.c > index d2ee1b2..71c6962 100644 > --- a/arch/arm64/kernel/alternative.c > +++ b/arch/arm64/kernel/alternative.c > @@ -80,6 +80,19 @@ static u32 get_alt_insn(struct alt_instr *alt, u32 > *insnptr, u32 *altinsnptr) > offset = target - (unsigned long)insnptr; > insn = aarch64_set_branch_offset(insn, offset); > } > + } else if (aarch64_insn_is_adrp(insn)) { > + s32 orig_offset, new_offset; > + unsigned long target; > + > + /* > + * If we're replacing an adrp instruction, which uses > PC-relative > + * immediate addressing, adjust the offset to reflect the new > + * PC. adrp operates on 4K aligned addresses. > + */ > + orig_offset = aarch64_insn_adrp_get_offset(insn); > + target = ((unsigned long)altinsnptr & ~0xfffUL) + orig_offset; > + new_offset = target - ((unsigned long)insnptr & ~0xfffUL);
The masking with ~0xfffUL might be nicer if you write it as align_down(ptr, SZ_4K); > + insn = aarch64_insn_adrp_set_offset(insn, new_offset); > } > > return insn; I wonder if we shouldn't have a catch-all for any instructions performing PC-relative operations here, because silent corruption of the instruction stream is pretty horrible. What other instructions are there? ADR, LDR (literal), ... ? Will
