[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:

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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 <redacted>

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+/* 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);

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-     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));

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-             dst_reg->var_off = tnum_add(ptr_reg->var_off, off_reg->var_off);

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+             tnum_add(&dst_reg->var_off, &ptr_reg->var_off,
+                     &off_reg->var_off);

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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

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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,