s390/bpf: Use relative long branches

Currently maximum JITed code size is limited to 64k, because JIT can
emit only relative short branches, whose range is limited by 64k in both
directions.

Teach JIT to use relative long branches. There are no compare+branch
relative long instructions, so using relative long branches consumes
more space due to having to having to emit an explicit comparison
instruction. Therefore do this only when relative short branch is not
enough.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20191118180340.68373-2-iii@linux.ibm.com

1 files changed, 126 insertions, 32 deletions

diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index 7bddb27c81e3..5ee1ebc6e448 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -189,6 +189,12 @@ static inline void reg_set_seen(struct bpf_jit *jit, u32 b1)
 	_EMIT4((op) | __pcrel);					\
 })
 
+#define EMIT4_PCREL_RIC(op, mask, target)			\
+({								\
+	int __rel = ((target) - jit->prg) / 2;			\
+	_EMIT4((op) | (mask) << 20 | (__rel & 0xffff));		\
+})
+
 #define _EMIT6(op1, op2)					\
 ({								\
 	if (jit->prg_buf) {					\
@@ -250,17 +256,22 @@ static inline void reg_set_seen(struct bpf_jit *jit, u32 b1)
 
 #define EMIT6_PCREL_RILB(op, b, target)				\
 ({								\
-	int rel = ((target) - jit->prg) / 2;			\
+	unsigned int rel = (int)((target) - jit->prg) / 2;	\
 	_EMIT6((op) | reg_high(b) << 16 | rel >> 16, rel & 0xffff);\
 	REG_SET_SEEN(b);					\
 })
 
 #define EMIT6_PCREL_RIL(op, target)				\
 ({								\
-	int rel = ((target) - jit->prg) / 2;			\
+	unsigned int rel = (int)((target) - jit->prg) / 2;	\
 	_EMIT6((op) | rel >> 16, rel & 0xffff);			\
 })
 
+#define EMIT6_PCREL_RILC(op, mask, target)			\
+({								\
+	EMIT6_PCREL_RIL((op) | (mask) << 20, (target));		\
+})
+
 #define _EMIT6_IMM(op, imm)					\
 ({								\
 	unsigned int __imm = (imm);				\
@@ -323,6 +334,22 @@ static bool is_codegen_pass(struct bpf_jit *jit)
 }
 
 /*
+ * Return whether "rel" can be encoded as a short PC-relative offset
+ */
+static bool is_valid_rel(int rel)
+{
+	return rel >= -65536 && rel <= 65534;
+}
+
+/*
+ * Return whether "off" can be reached using a short PC-relative offset
+ */
+static bool can_use_rel(struct bpf_jit *jit, int off)
+{
+	return is_valid_rel(off - jit->prg);
+}
+
+/*
  * Fill whole space with illegal instructions
  */
 static void jit_fill_hole(void *area, unsigned int size)
@@ -525,9 +552,9 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,
 				 int i, bool extra_pass)
 {
 	struct bpf_insn *insn = &fp->insnsi[i];
-	int jmp_off, last, insn_count = 1;
 	u32 dst_reg = insn->dst_reg;
 	u32 src_reg = insn->src_reg;
+	int last, insn_count = 1;
 	u32 *addrs = jit->addrs;
 	s32 imm = insn->imm;
 	s16 off = insn->off;
@@ -1071,9 +1098,17 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,
 		/* llgf %w1,map.max_entries(%b2) */
 		EMIT6_DISP_LH(0xe3000000, 0x0016, REG_W1, REG_0, BPF_REG_2,
 			      offsetof(struct bpf_array, map.max_entries));
-		/* clrj %b3,%w1,0xa,label0: if (u32)%b3 >= (u32)%w1 goto out */
-		EMIT6_PCREL_LABEL(0xec000000, 0x0077, BPF_REG_3,
-				  REG_W1, 0, 0xa);
+		/* if ((u32)%b3 >= (u32)%w1) goto out; */
+		if (!is_first_pass(jit) && can_use_rel(jit, jit->labels[0])) {
+			/* clrj %b3,%w1,0xa,label0 */
+			EMIT6_PCREL_LABEL(0xec000000, 0x0077, BPF_REG_3,
+					  REG_W1, 0, 0xa);
+		} else {
+			/* clr %b3,%w1 */
+			EMIT2(0x1500, BPF_REG_3, REG_W1);
+			/* brcl 0xa,label0 */
+			EMIT6_PCREL_RILC(0xc0040000, 0xa, jit->labels[0]);
+		}
 
 		/*
 		 * if (tail_call_cnt++ > MAX_TAIL_CALL_CNT)
@@ -1088,9 +1123,16 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,
 		EMIT4_IMM(0xa7080000, REG_W0, 1);
 		/* laal %w1,%w0,off(%r15) */
 		EMIT6_DISP_LH(0xeb000000, 0x00fa, REG_W1, REG_W0, REG_15, off);
-		/* clij %w1,MAX_TAIL_CALL_CNT,0x2,label0 */
-		EMIT6_PCREL_IMM_LABEL(0xec000000, 0x007f, REG_W1,
-				      MAX_TAIL_CALL_CNT, 0, 0x2);
+		if (!is_first_pass(jit) && can_use_rel(jit, jit->labels[0])) {
+			/* clij %w1,MAX_TAIL_CALL_CNT,0x2,label0 */
+			EMIT6_PCREL_IMM_LABEL(0xec000000, 0x007f, REG_W1,
+					      MAX_TAIL_CALL_CNT, 0, 0x2);
+		} else {
+			/* clfi %w1,MAX_TAIL_CALL_CNT */
+			EMIT6_IMM(0xc20f0000, REG_W1, MAX_TAIL_CALL_CNT);
+			/* brcl 0x2,label0 */
+			EMIT6_PCREL_RILC(0xc0040000, 0x2, jit->labels[0]);
+		}
 
 		/*
 		 * prog = array->ptrs[index];
@@ -1102,11 +1144,16 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,
 		EMIT4(0xb9160000, REG_1, BPF_REG_3);
 		/* sllg %r1,%r1,3: %r1 *= 8 */
 		EMIT6_DISP_LH(0xeb000000, 0x000d, REG_1, REG_1, REG_0, 3);
-		/* lg %r1,prog(%b2,%r1) */
-		EMIT6_DISP_LH(0xe3000000, 0x0004, REG_1, BPF_REG_2,
+		/* ltg %r1,prog(%b2,%r1) */
+		EMIT6_DISP_LH(0xe3000000, 0x0002, REG_1, BPF_REG_2,
 			      REG_1, offsetof(struct bpf_array, ptrs));
-		/* clgij %r1,0,0x8,label0 */
-		EMIT6_PCREL_IMM_LABEL(0xec000000, 0x007d, REG_1, 0, 0, 0x8);
+		if (!is_first_pass(jit) && can_use_rel(jit, jit->labels[0])) {
+			/* brc 0x8,label0 */
+			EMIT4_PCREL_RIC(0xa7040000, 0x8, jit->labels[0]);
+		} else {
+			/* brcl 0x8,label0 */
+			EMIT6_PCREL_RILC(0xc0040000, 0x8, jit->labels[0]);
+		}
 
 		/*
 		 * Restore registers before calling function
@@ -1263,36 +1310,83 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,
 		goto branch_oc;
 branch_ks:
 		is_jmp32 = BPF_CLASS(insn->code) == BPF_JMP32;
-		/* lgfi %w1,imm (load sign extend imm) */
-		EMIT6_IMM(0xc0010000, REG_W1, imm);
-		/* crj or cgrj %dst,%w1,mask,off */
-		EMIT6_PCREL(0xec000000, (is_jmp32 ? 0x0076 : 0x0064),
-			    dst_reg, REG_W1, i, off, mask);
+		/* cfi or cgfi %dst,imm */
+		EMIT6_IMM(is_jmp32 ? 0xc20d0000 : 0xc20c0000,
+			  dst_reg, imm);
+		if (!is_first_pass(jit) &&
+		    can_use_rel(jit, addrs[i + off + 1])) {
+			/* brc mask,off */
+			EMIT4_PCREL_RIC(0xa7040000,
+					mask >> 12, addrs[i + off + 1]);
+		} else {
+			/* brcl mask,off */
+			EMIT6_PCREL_RILC(0xc0040000,
+					 mask >> 12, addrs[i + off + 1]);
+		}
 		break;
 branch_ku:
 		is_jmp32 = BPF_CLASS(insn->code) == BPF_JMP32;
-		/* lgfi %w1,imm (load sign extend imm) */
-		EMIT6_IMM(0xc0010000, REG_W1, imm);
-		/* clrj or clgrj %dst,%w1,mask,off */
-		EMIT6_PCREL(0xec000000, (is_jmp32 ? 0x0077 : 0x0065),
-			    dst_reg, REG_W1, i, off, mask);
+		/* clfi or clgfi %dst,imm */
+		EMIT6_IMM(is_jmp32 ? 0xc20f0000 : 0xc20e0000,
+			  dst_reg, imm);
+		if (!is_first_pass(jit) &&
+		    can_use_rel(jit, addrs[i + off + 1])) {
+			/* brc mask,off */
+			EMIT4_PCREL_RIC(0xa7040000,
+					mask >> 12, addrs[i + off + 1]);
+		} else {
+			/* brcl mask,off */
+			EMIT6_PCREL_RILC(0xc0040000,
+					 mask >> 12, addrs[i + off + 1]);
+		}
 		break;
 branch_xs:
 		is_jmp32 = BPF_CLASS(insn->code) == BPF_JMP32;
-		/* crj or cgrj %dst,%src,mask,off */
-		EMIT6_PCREL(0xec000000, (is_jmp32 ? 0x0076 : 0x0064),
-			    dst_reg, src_reg, i, off, mask);
+		if (!is_first_pass(jit) &&
+		    can_use_rel(jit, addrs[i + off + 1])) {
+			/* crj or cgrj %dst,%src,mask,off */
+			EMIT6_PCREL(0xec000000, (is_jmp32 ? 0x0076 : 0x0064),
+				    dst_reg, src_reg, i, off, mask);
+		} else {
+			/* cr or cgr %dst,%src */
+			if (is_jmp32)
+				EMIT2(0x1900, dst_reg, src_reg);
+			else
+				EMIT4(0xb9200000, dst_reg, src_reg);
+			/* brcl mask,off */
+			EMIT6_PCREL_RILC(0xc0040000,
+					 mask >> 12, addrs[i + off + 1]);
+		}
 		break;
 branch_xu:
 		is_jmp32 = BPF_CLASS(insn->code) == BPF_JMP32;
-		/* clrj or clgrj %dst,%src,mask,off */
-		EMIT6_PCREL(0xec000000, (is_jmp32 ? 0x0077 : 0x0065),
-			    dst_reg, src_reg, i, off, mask);
+		if (!is_first_pass(jit) &&
+		    can_use_rel(jit, addrs[i + off + 1])) {
+			/* clrj or clgrj %dst,%src,mask,off */
+			EMIT6_PCREL(0xec000000, (is_jmp32 ? 0x0077 : 0x0065),
+				    dst_reg, src_reg, i, off, mask);
+		} else {
+			/* clr or clgr %dst,%src */
+			if (is_jmp32)
+				EMIT2(0x1500, dst_reg, src_reg);
+			else
+				EMIT4(0xb9210000, dst_reg, src_reg);
+			/* brcl mask,off */
+			EMIT6_PCREL_RILC(0xc0040000,
+					 mask >> 12, addrs[i + off + 1]);
+		}
 		break;
 branch_oc:
-		/* brc mask,jmp_off (branch instruction needs 4 bytes) */
-		jmp_off = addrs[i + off + 1] - (addrs[i + 1] - 4);
-		EMIT4_PCREL(0xa7040000 | mask << 8, jmp_off);
+		if (!is_first_pass(jit) &&
+		    can_use_rel(jit, addrs[i + off + 1])) {
+			/* brc mask,off */
+			EMIT4_PCREL_RIC(0xa7040000,
+					mask >> 12, addrs[i + off + 1]);
+		} else {
+			/* brcl mask,off */
+			EMIT6_PCREL_RILC(0xc0040000,
+					 mask >> 12, addrs[i + off + 1]);
+		}
 		break;
 	}
 	default: /* too complex, give up */