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

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Date:   Sun, 14 Jan 2018 00:03:42 +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

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>

Thanks,
Karim
---
 include/linux/tnum.h  |  4 +++-
 kernel/bpf/tnum.c     | 14 +++++++-------
 kernel/bpf/verifier.c | 11 ++++++-----
 3 files changed, 16 insertions(+), 13 deletions(-)

diff --git a/include/linux/tnum.h b/include/linux/tnum.h
index 0d2d3da..72938a0 100644
--- a/include/linux/tnum.h
+++ b/include/linux/tnum.h
@@ -13,6 +13,8 @@ struct tnum {
 };
 
 /* Constructors */
+/* 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);
 /* Subtract two tnums, return @a - @b */
 struct tnum tnum_sub(struct tnum a, struct tnum b);
 /* Bitwise-AND, return @a & @b */
diff --git a/kernel/bpf/tnum.c b/kernel/bpf/tnum.c
index 1f4bf68..89e3182 100644
--- a/kernel/bpf/tnum.c
+++ b/kernel/bpf/tnum.c
@@ -8,7 +8,6 @@
 #include <linux/kernel.h>
 #include <linux/tnum.h>
 
-#define TNUM(_v, _m)	(struct tnum){.value = _v, .mask = _m}
 /* A completely unknown value */
 const struct tnum tnum_unknown = { .value = 0, .mask = -1 };
 
@@ -43,16 +42,17 @@ struct tnum tnum_rshift(struct tnum a, u8 shift)
 	return TNUM(a.value >> shift, a.mask >> shift);
 }
 
-struct tnum tnum_add(struct tnum a, struct tnum b)
+void tnum_add(struct tnum *res, struct tnum *a, struct tnum *b)
 {
 	u64 sm, sv, sigma, chi, mu;
 
-	sm = a.mask + b.mask;
-	sv = a.value + b.value;
+	sm = a->mask + b->mask;
+	sv = a->value + b->value;
 	sigma = sm + sv;
 	chi = sigma ^ sv;
-	mu = chi | a.mask | b.mask;
-	return TNUM(sv & ~mu, mu);
+	mu = chi | a->mask | b->mask;
+	res->value = (sv & ~mu);
+	res->mask = mu;
 }
 
 struct tnum tnum_sub(struct tnum a, struct tnum b)
@@ -102,7 +102,7 @@ static struct tnum hma(struct tnum acc, u64 value, u64 mask)
 {
 	while (mask) {
 		if (mask & 1)
-			acc = tnum_add(acc, TNUM(0, value));
+			tnum_add(&acc, &acc, &TNUM(0, value));
 		mask >>= 1;
 		value <<= 1;
 	}
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index b414d6b..b31b1c4 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -999,7 +999,7 @@ static int check_pkt_ptr_alignment(struct bpf_verifier_env *env,
 	 */
 	ip_align = 2;
 
-	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));
 	if (!tnum_is_aligned(reg_off, size)) {
 		char tn_buf[48];
 
@@ -1971,7 +1970,8 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
 			dst_reg->umin_value = umin_ptr + umin_val;
 			dst_reg->umax_value = umax_ptr + umax_val;
 		}
-		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);
 		dst_reg->off = ptr_reg->off;
 		if (reg_is_pkt_pointer(ptr_reg)) {
 			dst_reg->id = ++env->id_gen;
@@ -2108,7 +2108,8 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
 			dst_reg->umin_value += umin_val;
 			dst_reg->umax_value += umax_val;
 		}
-		dst_reg->var_off = tnum_add(dst_reg->var_off, src_reg.var_off);
+		tnum_add(&dst_reg->var_off, &dst_reg->var_off,
+			&src_reg.var_off);
 		break;
 	case BPF_SUB:
 		if (signed_sub_overflows(dst_reg->smin_value, smax_val) ||
-- 
2.7.4