linux-kernel - [PATCH] kernel:bpf Remove structure passing and assignment to save stack and no coping structures

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Message-Id: <1516224723-20195-1-git-send-email-karim.eshapa@gmail.com>
Date:   Wed, 17 Jan 2018 23:32:03 +0200
From:   Karim Eshapa <karim.eshapa@...il.com>
To:     ast@...nel.org
Cc:     daniel@...earbox.net, ecree@...arflare.com, davem@...emloft.net,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        Karim Eshapa <karim.eshapa@...il.com>
Subject: [PATCH] kernel:bpf Remove structure passing and assignment to save stack and no coping structures

>On Sun, Jan 14, 2018 at 01:18:35PM +0200, Karim Eshapa wrote:
>> >> Use pointers to structure as arguments to function instead of coping
>> >> structures and less stack size. Also transfer TNUM(_v, _m) to
>> >> tnum.h file to be used in differnet files for creating anonymous structures
>> >> statically.
>> >>
>> >> Signed-off-by: Karim Eshapa <karim.eshapa@...il.com>
>> ...
>> >> +/* Statically tnum constant */
>> >> +#define TNUM(_v, _m) (struct tnum){.value = _v, .mask = _m}
>> >>  /* Represent a known constant as a tnum. */
>> >>  struct tnum tnum_const(u64 value);
>> >>  /* A completely unknown value */
>> >> @@ -26,7 +28,7 @@ struct tnum tnum_lshift(struct tnum a, u8 shift);
>> >>  /* Shift a tnum right (by a fixed shift) */
>> >>  struct tnum tnum_rshift(struct tnum a, u8 shift);
>> >>  /* Add two tnums, return @a + @b */
>> >> -struct tnum tnum_add(struct tnum a, struct tnum b);
>> >> +void tnum_add(struct tnum *res, struct tnum *a, struct tnum *b);
>> ...
>> >> -     reg_off = tnum_add(reg->var_off, tnum_const(ip_align + reg->off + off));
>> >> +     tnum_add(&reg_off, &reg->var_off, &TNUM(ip_align + reg->off + off, 0));
>> >>       if (!tnum_is_aligned(reg_off, size)) {
>> >>               char tn_buf[48];
>> >>
>> >> @@ -1023,8 +1023,7 @@ static int check_generic_ptr_alignment(struct bpf_verifier_env *env,
>> >>       /* Byte size accesses are always allowed. */
>> >>       if (!strict || size == 1)
>> >>               return 0;
>> >> -
>> >> -     reg_off = tnum_add(reg->var_off, tnum_const(reg->off + off));
>> >> +     tnum_add(&reg_off, &reg->var_off, &TNUM(reg->off + off, 0));
>> ...
> >> -             dst_reg->var_off = tnum_add(ptr_reg->var_off, off_reg->var_off);
>> >> +             tnum_add(&dst_reg->var_off, &ptr_reg->var_off,
>> >> +                     &off_reg->var_off);
>>
>> >Is it gnu or intel style of argumnets ? where is src or dest ?
>> >Can the same pointer be used as src and as dst ? etc, etc
>> >I don't think it saves stack either.
>> >I'd rather leave things as-is.
>>
>> It's not specific style but it's recommended when passing structure specially if
>> the structures have large sizes.
> and (dest, src0, src1) respectively.Although tnum structure isn't large but it saves
>> stack,we have 2 structure passed before calling and 1 returned to receive the return value.

>1. your patch has compile time warnings
>2. it doesn't reduce stack size.
>   For two functions that use tnum_add:
>   adjust_ptr_min_max_vals() before and after has exactly the same.
>   check_ptr_alignment() after your patch _increased_ stack size.
>3. text of verifier.o shrank 133 bytes while tnum.o increased 198

>Please do your homework next time.
>tnum code will stay as-is.

Thanks so much for your response,if there is any recommended tools
to test how your patch affect memory, performance and what's
going on because all accepted patches I sumbited was so trivial 
I'll be so appreciated.

Karim,