Re: [PATCH] arm64: bpf: fix signedness bug in loading 64-bit immediate

[Will Deacon]

On Fri, May 08, 2015 at 09:45:59AM +0100, Xi Wang wrote:
> On Fri, May 8, 2015 at 1:38 AM, Will Deacon <will.deacon@xxxxxxx> wrote:
> >> -             imm64 = (u64)insn1.imm << 32 | imm;
> >> +             imm64 = ((u64)(u32)insn1.imm) << 32 | (u64)(u32)imm;
> >
> > This seems a bit convoluted to me. Don't you just need to add a (u32)
> > cast to imm and that's it? The (u64)(u32) looks redundant.
> 
> You're right -  the second (u64) is redundant; the hope was to make
> the code easier to understand.  It's from the interpreter code in
> kernel/core/bpf.c, which uses (u64)(u32) as well.
> 
> >> -                     BPF_ALU64_IMM(BPF_MOV, R0, 1),
> >> +                     BPF_LD_IMM64(R0, 0x1ffffffffLL),
> >> +                     BPF_ALU64_IMM(BPF_RSH, R0, 32), /* R0 = 1 */
> >>                       BPF_EXIT_INSN(),
> >
> > This hunk should probably be a separate patch, unless you get Alexei's ack
> > for me to take it via the arm64 tree too.
> 
> I would be happy to split this into a separate patch if that works
> better, or simply drop this part.

Ok, I plan to apply the patch below for 4.1.

Will

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