Messages in this thread | | | Subject | Re: [PATCH 5/8] arm64: alternative: Add support for patching adrp instructions | From | Suzuki K Poulose <> | Date | Tue, 23 Aug 2016 10:39:01 +0100 |
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On 22/08/16 12:19, Will Deacon wrote: > 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 <will.deacon@arm.com> >> Cc: Marc Zyngier <marc.zyngier@arm.com> >> Cc: Andre Przywara <andre.przywara@arm.com> >> Cc: Mark Rutland <mark.rutland@arm.com> >> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> >> --- >> 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);
Right, that definitely looks better. Will change it.
> >> + 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
Correct, which is what happened initially when I didn't have the adrp handling ;-).
> stream is pretty horrible. What other instructions are there? ADR, LDR > (literal), ... ?
From a quick look, all the instructions under "Load register (literal)" :
i.e, LDR (literal) for GPR/FP_SIMD/32bit/64bit LDRSW (literal) PRFM (literal)
and Data processing instructions - immediate group with PC-relative addressing:
ADR, ADRP
I will add a check to catch the unsupported instructions in the alternative code.
Thanks Suzuki
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