Hi Catalin, Will,
On Tue, Sep 16, 2014 at 12:48 AM, Daniel Borkmann <dbork...@redhat.com> wrote:
[...]
> +static void jit_fill_hole(void *area, unsigned int size)
> +{
> + u32 *ptr;
> + /* We are guaranteed to have aligned memory. */
> + for (ptr = area; size >= sizeof(u32); size -= sizeof(u32))
> + *ptr++ = cpu_to_le32(AARCH64_BREAK_FAULT);
> +}
[...]
Out of curiosity, I looked at objdump of the above code.
0000000000000088 <jit_fill_hole>:
88: 71000c3f cmp w1, #0x3
8c: 54000149 b.ls b4 <jit_fill_hole+0x2c>
90: 51001022 sub w2, w1, #0x4
94: 927e7442 and x2, x2, #0xfffffffc
98: 91001042 add x2, x2, #0x4
9c: 8b020002 add x2, x0, x2
a0: 52840001 mov w1, #0x2000
// #8192 <-- loops here
a4: 72ba8401 movk w1, #0xd420, lsl #16
a8: b8004401 str w1, [x0],#4 <-- is there an
optimization such that we loop here?
ac: eb02001f cmp x0, x2
b0: 54ffff81 b.ne a0 <jit_fill_hole+0x18>
b4: d65f03c0 ret
I'm wondering if there's any optimizations that'll generate code that
loops at 0xa8 instead of 0xa0. w1 only needs to loaded with the
constant once, but here we're reloading it on every iteration of the
loop.
Thanks,
z
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