Merge branch 'compressed-JITed-insn'

Luke Nelson says:

====================
his patch series enables using compressed riscv (RVC) instructions
in the rv64 BPF JIT.

RVC is a standard riscv extension that adds a set of compressed,
2-byte instructions that can replace some regular 4-byte instructions
for improved code density.

This series first modifies the JIT to support using 2-byte instructions
(e.g., in jump offset computations), then adds RVC encoding and
helper functions, and finally uses the helper functions to optimize
the rv64 JIT.

I used our formal verification framework, Serval, to verify the
correctness of the RVC encodings and their uses in the rv64 JIT.

The JIT continues to pass all tests in lib/test_bpf.c, and introduces
no new failures to test_verifier; both with and without RVC being enabled.

The following are examples of the JITed code for the verifier selftest
"direct packet read test#3 for CGROUP_SKB OK", without and with RVC
enabled, respectively. The former uses 178 bytes, and the latter uses 112,
for a ~37% reduction in code size for this example.

Without RVC:

   0: 02000813    addi  a6,zero,32
   4: fd010113    addi  sp,sp,-48
   8: 02813423    sd    s0,40(sp)
   c: 02913023    sd    s1,32(sp)
  10: 01213c23    sd    s2,24(sp)
  14: 01313823    sd    s3,16(sp)
  18: 01413423    sd    s4,8(sp)
  1c: 03010413    addi  s0,sp,48
  20: 03056683    lwu   a3,48(a0)
  24: 02069693    slli  a3,a3,0x20
  28: 0206d693    srli  a3,a3,0x20
  2c: 03456703    lwu   a4,52(a0)
  30: 02071713    slli  a4,a4,0x20
  34: 02075713    srli  a4,a4,0x20
  38: 03856483    lwu   s1,56(a0)
  3c: 02049493    slli  s1,s1,0x20
  40: 0204d493    srli  s1,s1,0x20
  44: 03c56903    lwu   s2,60(a0)
  48: 02091913    slli  s2,s2,0x20
  4c: 02095913    srli  s2,s2,0x20
  50: 04056983    lwu   s3,64(a0)
  54: 02099993    slli  s3,s3,0x20
  58: 0209d993    srli  s3,s3,0x20
  5c: 09056a03    lwu   s4,144(a0)
  60: 020a1a13    slli  s4,s4,0x20
  64: 020a5a13    srli  s4,s4,0x20
  68: 00900313    addi  t1,zero,9
  6c: 006a7463    bgeu  s4,t1,0x74
  70: 00000a13    addi  s4,zero,0
  74: 02d52823    sw    a3,48(a0)
  78: 02e52a23    sw    a4,52(a0)
  7c: 02952c23    sw    s1,56(a0)
  80: 03252e23    sw    s2,60(a0)
  84: 05352023    sw    s3,64(a0)
  88: 00000793    addi  a5,zero,0
  8c: 02813403    ld    s0,40(sp)
  90: 02013483    ld    s1,32(sp)
  94: 01813903    ld    s2,24(sp)
  98: 01013983    ld    s3,16(sp)
  9c: 00813a03    ld    s4,8(sp)
  a0: 03010113    addi  sp,sp,48
  a4: 00078513    addi  a0,a5,0
  a8: 00008067    jalr  zero,0(ra)

With RVC:

   0:   02000813    addi    a6,zero,32
   4:   7179        c.addi16sp  sp,-48
   6:   f422        c.sdsp  s0,40(sp)
   8:   f026        c.sdsp  s1,32(sp)
   a:   ec4a        c.sdsp  s2,24(sp)
   c:   e84e        c.sdsp  s3,16(sp)
   e:   e452        c.sdsp  s4,8(sp)
  10:   1800        c.addi4spn  s0,sp,48
  12:   03056683    lwu     a3,48(a0)
  16:   1682        c.slli  a3,0x20
  18:   9281        c.srli  a3,0x20
  1a:   03456703    lwu     a4,52(a0)
  1e:   1702        c.slli  a4,0x20
  20:   9301        c.srli  a4,0x20
  22:   03856483    lwu     s1,56(a0)
  26:   1482        c.slli  s1,0x20
  28:   9081        c.srli  s1,0x20
  2a:   03c56903    lwu     s2,60(a0)
  2e:   1902        c.slli  s2,0x20
  30:   02095913    srli    s2,s2,0x20
  34:   04056983    lwu     s3,64(a0)
  38:   1982        c.slli  s3,0x20
  3a:   0209d993    srli    s3,s3,0x20
  3e:   09056a03    lwu     s4,144(a0)
  42:   1a02        c.slli  s4,0x20
  44:   020a5a13    srli    s4,s4,0x20
  48:   4325        c.li    t1,9
  4a:   006a7363    bgeu    s4,t1,0x50
  4e:   4a01        c.li    s4,0
  50:   d914        c.sw    a3,48(a0)
  52:   d958        c.sw    a4,52(a0)
  54:   dd04        c.sw    s1,56(a0)
  56:   03252e23    sw      s2,60(a0)
  5a:   05352023    sw      s3,64(a0)
  5e:   4781        c.li    a5,0
  60:   7422        c.ldsp  s0,40(sp)
  62:   7482        c.ldsp  s1,32(sp)
  64:   6962        c.ldsp  s2,24(sp)
  66:   69c2        c.ldsp  s3,16(sp)
  68:   6a22        c.ldsp  s4,8(sp)
  6a:   6145        c.addi16sp  sp,48
  6c:   853e        c.mv    a0,a5
  6e:   8082        c.jr    ra

RFC -> v1:
  - From Björn Töpel:
    * Changed RVOFF macro to static inline "ninsns_rvoff".
    * Changed return type of rvc_ functions from u32 to u16.
    * Changed sizeof(u16) to sizeof(*ctx->insns).
  * Factored unsigned immediate checks into helper functions
    (is_8b_uint, etc.)
  * Changed to use IS_ENABLED instead of #ifdef to check if RVC is
    enabled.
  * Changed type of immediate arguments to rvc_* encoding to u32
    to avoid issues from promotion of u16 to signed int.
  * Cleaned up RVC checks in emit_{addi,slli,srli,srai}.
    + Wrapped lines at 100 instead of 80 columns for increased clarity.
	+ Move !imm checks into each branch instead of checking
	  separately.
	+ Strengthed checks for c.{slli,srli,srai} to check that
	  imm < XLEN. Otherwise, imm could be non-zero but the lower
	  XLEN bits could all be zero, leading to invalid RVC encoding.
  * Changed emit_imm to sign-extend the 12-bit value in "lower"
    + The immediate checks for emit_{addiw,li,addi} use signed
	  comparisons, so this enables the RVC variants to be used
	  more often (e.g., if val == -1, then lower should be -1
	  as opposed to 4095).
====================
Reviewed-by: Björn Töpel <bjorn.topel@gmail.com>
Acked-by: Björn Töpel <bjorn.topel@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

arch/riscv/net/bpf_jit_comp32.c

@@ -644,7 +644,7 @@ static int emit_branch_r64(const s8 *src1, const s8 *src2, s32 rvoff,
 
 	e = ctx->ninsns;
 	/* Adjust for extra insns. */
-	rvoff -= (e - s) << 2;
+	rvoff -= ninsns_rvoff(e - s);
 	emit_jump_and_link(RV_REG_ZERO, rvoff, true, ctx);
 	return 0;
 }
@@ -713,7 +713,7 @@ static int emit_bcc(u8 op, u8 rd, u8 rs, int rvoff, struct rv_jit_context *ctx)
 	if (far) {
 		e = ctx->ninsns;
 		/* Adjust for extra insns. */
-		rvoff -= (e - s) << 2;
+		rvoff -= ninsns_rvoff(e - s);
 		emit_jump_and_link(RV_REG_ZERO, rvoff, true, ctx);
 	}
 	return 0;
@@ -731,7 +731,7 @@ static int emit_branch_r32(const s8 *src1, const s8 *src2, s32 rvoff,
 
 	e = ctx->ninsns;
 	/* Adjust for extra insns. */
-	rvoff -= (e - s) << 2;
+	rvoff -= ninsns_rvoff(e - s);
 
 	if (emit_bcc(op, lo(rs1), lo(rs2), rvoff, ctx))
 		return -1;
@@ -795,7 +795,7 @@ static int emit_bpf_tail_call(int insn, struct rv_jit_context *ctx)
 	 * if (index >= max_entries)
 	 *   goto out;
 	 */
-	off = (tc_ninsn - (ctx->ninsns - start_insn)) << 2;
+	off = ninsns_rvoff(tc_ninsn - (ctx->ninsns - start_insn));
 	emit_bcc(BPF_JGE, lo(idx_reg), RV_REG_T1, off, ctx);
 
 	/*
@@ -804,7 +804,7 @@ static int emit_bpf_tail_call(int insn, struct rv_jit_context *ctx)
 	 *   goto out;
 	 */
 	emit(rv_addi(RV_REG_T1, RV_REG_TCC, -1), ctx);
-	off = (tc_ninsn - (ctx->ninsns - start_insn)) << 2;
+	off = ninsns_rvoff(tc_ninsn - (ctx->ninsns - start_insn));
 	emit_bcc(BPF_JSLT, RV_REG_TCC, RV_REG_ZERO, off, ctx);
 
 	/*
@@ -818,7 +818,7 @@ static int emit_bpf_tail_call(int insn, struct rv_jit_context *ctx)
 	if (is_12b_check(off, insn))
 		return -1;
 	emit(rv_lw(RV_REG_T0, off, RV_REG_T0), ctx);
-	off = (tc_ninsn - (ctx->ninsns - start_insn)) << 2;
+	off = ninsns_rvoff(tc_ninsn - (ctx->ninsns - start_insn));
 	emit_bcc(BPF_JEQ, RV_REG_T0, RV_REG_ZERO, off, ctx);
 
 	/*
@@ -1214,7 +1214,7 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
 			emit_imm32(tmp2, imm, ctx);
 			src = tmp2;
 			e = ctx->ninsns;
-			rvoff -= (e - s) << 2;
+			rvoff -= ninsns_rvoff(e - s);
 		}
 
 		if (is64)

arch/riscv/net/bpf_jit_core.c

@@ -73,7 +73,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
 
 	if (ctx->offset) {
 		extra_pass = true;
-		image_size = sizeof(u32) * ctx->ninsns;
+		image_size = sizeof(*ctx->insns) * ctx->ninsns;
 		goto skip_init_ctx;
 	}
 
@@ -103,7 +103,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
 			if (jit_data->header)
 				break;
 
-			image_size = sizeof(u32) * ctx->ninsns;
+			image_size = sizeof(*ctx->insns) * ctx->ninsns;
 			jit_data->header =
 				bpf_jit_binary_alloc(image_size,
 						     &jit_data->image,
@@ -114,7 +114,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
 				goto out_offset;
 			}
 
-			ctx->insns = (u32 *)jit_data->image;
+			ctx->insns = (u16 *)jit_data->image;
 			/*
 			 * Now, when the image is allocated, the image can
 			 * potentially shrink more (auipc/jalr -> jal).