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    SubjectRe: [PATCH 4/4] ARM: net fix emit_udiv() for BPF_ALU | BPF_DIV | BPF_K intruction.
    On Wed, Apr 29, 2015 at 03:37:37PM +0200, Nicolas Schichan wrote:
    > In that case, emit_udiv() will be called with rn == ARM_R0 (r_scratch)
    > and loading rm first into ARM_R0 will result in jit_udiv() function
    > being called the same dividend and divisor. Fix that by loading rn
    > first into ARM_R1 and then rm into ARM_R0.
    >
    > Signed-off-by: Nicolas Schichan <nschichan@freebox.fr>
    > ---
    > arch/arm/net/bpf_jit_32.c | 4 ++--
    > 1 file changed, 2 insertions(+), 2 deletions(-)
    >
    > diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c
    > index b5f470d..ffaf311 100644
    > --- a/arch/arm/net/bpf_jit_32.c
    > +++ b/arch/arm/net/bpf_jit_32.c
    > @@ -449,10 +449,10 @@ static inline void emit_udiv(u8 rd, u8 rm, u8 rn, struct jit_ctx *ctx)
    > return;
    > }
    > #endif
    > - if (rm != ARM_R0)
    > - emit(ARM_MOV_R(ARM_R0, rm), ctx);
    > if (rn != ARM_R1)
    > emit(ARM_MOV_R(ARM_R1, rn), ctx);
    > + if (rm != ARM_R0)
    > + emit(ARM_MOV_R(ARM_R0, rm), ctx);

    I don't think you've thought enough about this. What if rm is ARM_R1?
    What if rn = ARM_R0 and rm = ARM_R1?

    How about:

    if (rn == ARM_R0 && rm == ARM_R1) {
    emit(ARM_MOV_R(ARM_R3, rn), ctx); // r3 <- r0(rn)
    emit(ARM_MOV_R(ARM_R0, rm), ctx); // r0 <- r1(rm)
    emit(ARM_MOV_R(ARM_R1, ARM_R3), ctx); // r1 <- r3
    } else if (rn == ARM_R0) {
    emit(ARM_MOV_R(ARM_R1, rn), ctx); // r1 <- rn
    if (rm != ARM_R0)
    emit(ARM_MOV_R(ARM_R0, rm), ctx); // r0 <- rm
    } else {
    if (rm != ARM_R0)
    emit(ARM_MOV_R(ARM_R0, rm), ctx); // r0 <- rm
    if (rn != ARM_R1)
    emit(ARM_MOV_R(ARM_R1, rn), ctx); // r1 <- rn
    }

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