diff --git a/executor/common_linux.h b/executor/common_linux.h
index 6c43907b..90a87358 100644
--- a/executor/common_linux.h
+++ b/executor/common_linux.h
@@ -7,6 +7,7 @@
 #define _GNU_SOURCE
 #endif
 
+#include <endian.h>
 #include <sys/syscall.h>
 #include <unistd.h>
 #if defined(SYZ_EXECUTOR) || defined(SYZ_THREADED) || defined(SYZ_COLLIDE)
diff --git a/executor/executor.h b/executor/executor.h
index 13072a35..84cefecf 100644
--- a/executor/executor.h
+++ b/executor/executor.h
@@ -183,6 +183,7 @@ uint32_t* write_output(uint32_t v);
 void write_completed(uint32_t completed);
 uint64_t read_input(uint64_t** input_posp, bool peek = false);
 uint64_t read_arg(uint64_t** input_posp);
+uint64_t read_const_arg(uint64_t** input_posp, uint64_t* size_p, uint64_t* bf_off_p, uint64_t* bf_len_p);
 uint64_t read_result(uint64_t** input_posp);
 void copyin(char* addr, uint64_t val, uint64_t size, uint64_t bf_off, uint64_t bf_len);
 uint64_t copyout(char* addr, uint64_t size);
@@ -309,22 +310,22 @@ retry:
 		if (call_num == instr_copyin) {
 			char* addr = (char*)read_input(&input_pos);
 			uint64_t typ = read_input(&input_pos);
-			uint64_t size = read_input(&input_pos);
 			debug("copyin to %p\n", addr);
 			switch (typ) {
 			case arg_const: {
-				uint64_t arg = read_input(&input_pos);
-				uint64_t bf_off = read_input(&input_pos);
-				uint64_t bf_len = read_input(&input_pos);
+				uint64_t size, bf_off, bf_len;
+				uint64_t arg = read_const_arg(&input_pos, &size, &bf_off, &bf_len);
 				copyin(addr, arg, size, bf_off, bf_len);
 				break;
 			}
 			case arg_result: {
+				uint64_t size = read_input(&input_pos);
 				uint64_t val = read_result(&input_pos);
 				copyin(addr, val, size, 0, 0);
 				break;
 			}
 			case arg_data: {
+				uint64_t size = read_input(&input_pos);
 				NONFAILING(memcpy(addr, input_pos, size));
 				// Read out the data.
 				for (uint64_t i = 0; i < (size + 7) / 8; i++)
@@ -333,12 +334,12 @@ retry:
 			}
 			case arg_csum: {
 				debug("checksum found at %llx\n", addr);
+				uint64_t size = read_input(&input_pos);
 				char* csum_addr = addr;
-				uint64_t csum_size = size;
 				uint64_t csum_kind = read_input(&input_pos);
 				switch (csum_kind) {
 				case arg_csum_inet: {
-					if (csum_size != 2) {
+					if (size != 2) {
 						fail("inet checksum must be 2 bytes, not %lu", size);
 					}
 					debug("calculating checksum for %llx\n", csum_addr);
@@ -725,25 +726,46 @@ uint64_t copyout(char* addr, uint64_t size)
 uint64_t read_arg(uint64_t** input_posp)
 {
 	uint64_t typ = read_input(input_posp);
-	uint64_t size = read_input(input_posp);
-	(void)size;
-	uint64_t arg = 0;
 	switch (typ) {
 	case arg_const: {
-		arg = read_input(input_posp);
-		// Bitfields can't be args of a normal syscall, so just ignore them.
-		read_input(input_posp); // bit field offset
-		read_input(input_posp); // bit field length
-		break;
+		uint64_t size, bf_off, bf_len;
+		return read_const_arg(input_posp, &size, &bf_off, &bf_len);
 	}
 	case arg_result: {
-		arg = read_result(input_posp);
-		break;
+		read_input(input_posp); // size
+		return read_result(input_posp);
 	}
 	default:
 		fail("bad argument type %lu", typ);
 	}
-	return arg;
+}
+
+uint64_t read_const_arg(uint64_t** input_posp, uint64_t* size_p, uint64_t* bf_off_p, uint64_t* bf_len_p)
+{
+	uint64_t meta = read_input(input_posp);
+	uint64_t val = read_input(input_posp);
+	*size_p = meta & 0xff;
+	bool be = meta & (1 << 8);
+	*bf_off_p = (meta >> 16) & 0xff;
+	*bf_len_p = (meta >> 24) & 0xff;
+	uint64_t pid_stride = meta >> 32;
+	val += pid_stride * flag_pid;
+	if (be) {
+		switch (*size_p) {
+		case 2:
+			val = htobe16(val);
+			break;
+		case 4:
+			val = htobe32(val);
+			break;
+		case 8:
+			val = htobe64(val);
+			break;
+		default:
+			fail("bad big-endian int size %d", (int)*size_p);
+		}
+	}
+	return val;
 }
 
 uint64_t read_result(uint64_t** input_posp)
diff --git a/pkg/csource/csource.go b/pkg/csource/csource.go
index 1fb00d1c..38814c3b 100644
--- a/pkg/csource/csource.go
+++ b/pkg/csource/csource.go
@@ -42,7 +42,7 @@ func Write(p *prog.Prog, opts Options) ([]byte, error) {
 	ctx.generateSyscallDefines()
 
 	exec := make([]byte, prog.ExecBufferSize)
-	progSize, err := ctx.p.SerializeForExec(exec, 0)
+	progSize, err := ctx.p.SerializeForExec(exec)
 	if err != nil {
 		return nil, fmt.Errorf("failed to serialize program: %v", err)
 	}
@@ -54,6 +54,9 @@ func Write(p *prog.Prog, opts Options) ([]byte, error) {
 	if nvar != 0 {
 		ctx.printf("long r[%v];\n", nvar)
 	}
+	if opts.Procs > 1 {
+		ctx.printf("uint64_t procid;\n")
+	}
 
 	if !opts.Repeat {
 		ctx.generateTestFunc(calls, nvar, "loop")
@@ -102,6 +105,7 @@ func Write(p *prog.Prog, opts Options) ([]byte, error) {
 			ctx.print("\tint i;")
 			ctx.printf("\tfor (i = 0; i < %v; i++) {\n", opts.Procs)
 			ctx.print("\t\tif (fork() == 0) {\n")
+			ctx.printf("\t\t\tprocid = i;\n")
 			if opts.HandleSegv {
 				ctx.printf("\t\t\tinstall_segv_handler();\n")
 			}
@@ -256,16 +260,6 @@ func (ctx *context) generateSyscallDefines() {
 }
 
 func (ctx *context) generateCalls(p prog.ExecProg) ([]string, uint64) {
-	resultRef := func(arg prog.ExecArgResult) string {
-		res := fmt.Sprintf("r[%v]", arg.Index)
-		if arg.DivOp != 0 {
-			res = fmt.Sprintf("%v/%v", res, arg.DivOp)
-		}
-		if arg.AddOp != 0 {
-			res = fmt.Sprintf("%v+%v", res, arg.AddOp)
-		}
-		return res
-	}
 	var calls []string
 	csumSeq := 0
 	for ci, call := range p.Calls {
@@ -275,15 +269,16 @@ func (ctx *context) generateCalls(p prog.ExecProg) ([]string, uint64) {
 			switch arg := copyin.Arg.(type) {
 			case prog.ExecArgConst:
 				if arg.BitfieldOffset == 0 && arg.BitfieldLength == 0 {
-					fmt.Fprintf(w, "\tNONFAILING(*(uint%v_t*)0x%x = (uint%v_t)0x%x);\n",
-						arg.Size*8, copyin.Addr, arg.Size*8, arg.Value)
+					fmt.Fprintf(w, "\tNONFAILING(*(uint%v_t*)0x%x = %v);\n",
+						arg.Size*8, copyin.Addr, ctx.constArgToStr(arg))
 				} else {
-					fmt.Fprintf(w, "\tNONFAILING(STORE_BY_BITMASK(uint%v_t, 0x%x, 0x%x, %v, %v));\n",
-						arg.Size*8, copyin.Addr, arg.Value, arg.BitfieldOffset, arg.BitfieldLength)
+					fmt.Fprintf(w, "\tNONFAILING(STORE_BY_BITMASK(uint%v_t, 0x%x, %v, %v, %v));\n",
+						arg.Size*8, copyin.Addr, ctx.constArgToStr(arg),
+						arg.BitfieldOffset, arg.BitfieldLength)
 				}
 			case prog.ExecArgResult:
 				fmt.Fprintf(w, "\tNONFAILING(*(uint%v_t*)0x%x = %v);\n",
-					arg.Size*8, copyin.Addr, resultRef(arg))
+					arg.Size*8, copyin.Addr, ctx.resultArgToStr(arg))
 			case prog.ExecArgData:
 				fmt.Fprintf(w, "\tNONFAILING(memcpy((void*)0x%x, \"%s\", %v));\n",
 					copyin.Addr, toCString(arg.Data), len(arg.Data))
@@ -349,9 +344,9 @@ func (ctx *context) generateCalls(p prog.ExecProg) ([]string, uint64) {
 				}
 				switch arg := arg.(type) {
 				case prog.ExecArgConst:
-					fmt.Fprintf(w, "0x%xul", arg.Value)
+					fmt.Fprintf(w, "%v", ctx.constArgToStr(arg))
 				case prog.ExecArgResult:
-					fmt.Fprintf(w, "%v", resultRef(arg))
+					fmt.Fprintf(w, "%v", ctx.resultArgToStr(arg))
 				default:
 					panic(fmt.Sprintf("unknown arg type: %+v", arg))
 				}
@@ -382,6 +377,29 @@ func (ctx *context) generateCalls(p prog.ExecProg) ([]string, uint64) {
 	return calls, p.NumVars
 }
 
+func (ctx *context) constArgToStr(arg prog.ExecArgConst) string {
+	mask := (uint64(1) << (arg.Size * 8)) - 1
+	val := fmt.Sprintf("0x%x", arg.Value&mask)
+	if ctx.opts.Procs > 1 && arg.PidStride != 0 {
+		val += fmt.Sprintf("+procid*0x%xul", arg.PidStride)
+	}
+	if arg.BigEndian {
+		val = fmt.Sprintf("htobe%v(%v)", arg.Size*8, val)
+	}
+	return val
+}
+
+func (ctx *context) resultArgToStr(arg prog.ExecArgResult) string {
+	res := fmt.Sprintf("r[%v]", arg.Index)
+	if arg.DivOp != 0 {
+		res = fmt.Sprintf("%v/%v", res, arg.DivOp)
+	}
+	if arg.AddOp != 0 {
+		res = fmt.Sprintf("%v+%v", res, arg.AddOp)
+	}
+	return res
+}
+
 func toCString(data []byte) []byte {
 	if len(data) == 0 {
 		return nil
diff --git a/pkg/csource/linux_common.go b/pkg/csource/linux_common.go
index 14a7d91d..5d207bd1 100644
--- a/pkg/csource/linux_common.go
+++ b/pkg/csource/linux_common.go
@@ -8,6 +8,7 @@ var commonHeaderLinux = `
 #define _GNU_SOURCE
 #endif
 
+#include <endian.h>
 #include <sys/syscall.h>
 #include <unistd.h>
 #if defined(SYZ_EXECUTOR) || defined(SYZ_THREADED) || defined(SYZ_COLLIDE)
diff --git a/pkg/ipc/ipc.go b/pkg/ipc/ipc.go
index 7aa57ded..5b716b6e 100644
--- a/pkg/ipc/ipc.go
+++ b/pkg/ipc/ipc.go
@@ -305,7 +305,7 @@ func (env *Env) Exec(opts *ExecOpts, p *prog.Prog) (output []byte, info []CallIn
 		})
 	}
 	// Copy-in serialized program.
-	progSize, err := p.SerializeForExec(env.in, env.pid)
+	progSize, err := p.SerializeForExec(env.in)
 	if err != nil {
 		err0 = fmt.Errorf("executor %v: failed to serialize: %v", env.pid, err)
 		return
diff --git a/prog/checksum.go b/prog/checksum.go
index b5226e71..f1d2c0dd 100644
--- a/prog/checksum.go
+++ b/prog/checksum.go
@@ -59,7 +59,7 @@ func extractHeaderParamsIPv6(arg Arg) (Arg, Arg) {
 	return srcAddr, dstAddr
 }
 
-func composePseudoCsumIPv4(tcpPacket, srcAddr, dstAddr Arg, protocol uint8, pid int) CsumInfo {
+func composePseudoCsumIPv4(tcpPacket, srcAddr, dstAddr Arg, protocol uint8) CsumInfo {
 	info := CsumInfo{Kind: CsumInet}
 	info.Chunks = append(info.Chunks, CsumChunk{CsumChunkArg, srcAddr, 0, 0})
 	info.Chunks = append(info.Chunks, CsumChunk{CsumChunkArg, dstAddr, 0, 0})
@@ -69,7 +69,7 @@ func composePseudoCsumIPv4(tcpPacket, srcAddr, dstAddr Arg, protocol uint8, pid
 	return info
 }
 
-func composePseudoCsumIPv6(tcpPacket, srcAddr, dstAddr Arg, protocol uint8, pid int) CsumInfo {
+func composePseudoCsumIPv6(tcpPacket, srcAddr, dstAddr Arg, protocol uint8) CsumInfo {
 	info := CsumInfo{Kind: CsumInet}
 	info.Chunks = append(info.Chunks, CsumChunk{CsumChunkArg, srcAddr, 0, 0})
 	info.Chunks = append(info.Chunks, CsumChunk{CsumChunkArg, dstAddr, 0, 0})
@@ -95,7 +95,7 @@ func findCsummedArg(arg Arg, typ *CsumType, parentsMap map[Arg]Arg) Arg {
 	panic(fmt.Sprintf("csum field '%v' references non existent field '%v'", typ.FieldName(), typ.Buf))
 }
 
-func calcChecksumsCall(c *Call, pid int) map[Arg]CsumInfo {
+func calcChecksumsCall(c *Call) map[Arg]CsumInfo {
 	var inetCsumFields []Arg
 	var pseudoCsumFields []Arg
 
@@ -172,9 +172,9 @@ func calcChecksumsCall(c *Call, pid int) map[Arg]CsumInfo {
 		protocol := uint8(typ.Protocol)
 		var info CsumInfo
 		if ipv4HeaderParsed {
-			info = composePseudoCsumIPv4(csummedArg, ipSrcAddr, ipDstAddr, protocol, pid)
+			info = composePseudoCsumIPv4(csummedArg, ipSrcAddr, ipDstAddr, protocol)
 		} else {
-			info = composePseudoCsumIPv6(csummedArg, ipSrcAddr, ipDstAddr, protocol, pid)
+			info = composePseudoCsumIPv6(csummedArg, ipSrcAddr, ipDstAddr, protocol)
 		}
 		csumMap[arg] = info
 	}
diff --git a/prog/checksum_test.go b/prog/checksum_test.go
index d466cf2c..75e18ab7 100644
--- a/prog/checksum_test.go
+++ b/prog/checksum_test.go
@@ -15,12 +15,12 @@ func TestChecksumCalcRandom(t *testing.T) {
 	for i := 0; i < iters; i++ {
 		p := target.Generate(rs, 10, nil)
 		for _, call := range p.Calls {
-			CalcChecksumsCall(call, i%32)
+			CalcChecksumsCall(call)
 		}
 		for try := 0; try <= 10; try++ {
 			p.Mutate(rs, 10, nil, nil)
 			for _, call := range p.Calls {
-				CalcChecksumsCall(call, i%32)
+				CalcChecksumsCall(call)
 			}
 		}
 	}
diff --git a/prog/decodeexec.go b/prog/decodeexec.go
index e62569b4..a1646178 100644
--- a/prog/decodeexec.go
+++ b/prog/decodeexec.go
@@ -38,6 +38,8 @@ type ExecArgConst struct {
 	Value          uint64
 	BitfieldOffset uint64
 	BitfieldLength uint64
+	PidStride      uint64
+	BigEndian      bool
 }
 
 type ExecArgResult struct {
@@ -127,11 +129,14 @@ func (dec *execDecoder) parse() {
 func (dec *execDecoder) readArg() ExecArg {
 	switch typ := dec.read(); typ {
 	case execArgConst:
+		meta := dec.read()
 		return ExecArgConst{
-			Size:           dec.read(),
 			Value:          dec.read(),
-			BitfieldOffset: dec.read(),
-			BitfieldLength: dec.read(),
+			Size:           meta & 0xff,
+			BitfieldOffset: (meta >> 16) & 0xff,
+			BitfieldLength: (meta >> 24) & 0xff,
+			PidStride:      meta >> 32,
+			BigEndian:      (meta & (1 << 8)) != 0,
 		}
 	case execArgResult:
 		return ExecArgResult{
diff --git a/prog/encoding_test.go b/prog/encoding_test.go
index 5fce3014..6c063b5a 100644
--- a/prog/encoding_test.go
+++ b/prog/encoding_test.go
@@ -159,7 +159,7 @@ func TestDeserialize(t *testing.T) {
 				t.Fatalf("deserialization should have failed with:\n%s\ndata:\n%s\n",
 					test.err, test.data)
 			}
-			p.SerializeForExec(buf, 0)
+			p.SerializeForExec(buf)
 		}
 	}
 }
diff --git a/prog/encodingexec.go b/prog/encodingexec.go
index 86ec1f63..2a41e4a5 100644
--- a/prog/encodingexec.go
+++ b/prog/encodingexec.go
@@ -73,7 +73,7 @@ func (s ByPhysicalAddr) Less(i, j int) bool {
 // SerializeForExec serializes program p for execution by process pid into the provided buffer.
 // Returns number of bytes written to the buffer.
 // If the provided buffer is too small for the program an error is returned.
-func (p *Prog) SerializeForExec(buffer []byte, pid int) (int, error) {
+func (p *Prog) SerializeForExec(buffer []byte) (int, error) {
 	if debug {
 		if err := p.validate(); err != nil {
 			panic(fmt.Errorf("serializing invalid program: %v", err))
@@ -88,7 +88,7 @@ func (p *Prog) SerializeForExec(buffer []byte, pid int) (int, error) {
 	}
 	for _, c := range p.Calls {
 		// Calculate checksums.
-		csumMap := calcChecksumsCall(c, pid)
+		csumMap := calcChecksumsCall(c)
 		var csumUses map[Arg]bool
 		if csumMap != nil {
 			csumUses = make(map[Arg]bool)
@@ -125,7 +125,7 @@ func (p *Prog) SerializeForExec(buffer []byte, pid int) (int, error) {
 					if !IsPad(arg1.Type()) && arg1.Type().Dir() != DirOut {
 						w.write(execInstrCopyin)
 						w.write(addr)
-						w.writeArg(arg1, pid)
+						w.writeArg(arg1)
 					}
 				})
 			}
@@ -181,7 +181,7 @@ func (p *Prog) SerializeForExec(buffer []byte, pid int) (int, error) {
 		}
 		w.write(uint64(len(c.Args)))
 		for _, arg := range c.Args {
-			w.writeArg(arg, pid)
+			w.writeArg(arg)
 		}
 		// Generate copyout instructions that persist interesting return values.
 		foreachArg(c, func(arg, base Arg, _ *[]Arg) {
@@ -258,21 +258,15 @@ func (w *execContext) write(v uint64) {
 	w.buf = w.buf[8:]
 }
 
-func (w *execContext) writeArg(arg Arg, pid int) {
+func (w *execContext) writeArg(arg Arg) {
 	switch a := arg.(type) {
 	case *ConstArg:
-		w.write(execArgConst)
-		w.write(a.Size())
-		w.write(a.Value(pid))
-		w.write(a.Type().BitfieldOffset())
-		w.write(a.Type().BitfieldLength())
+		val, pidStride, bigEndian := a.Value()
+		w.writeConstArg(a.Size(), val, a.Type().BitfieldOffset(), a.Type().BitfieldLength(),
+			pidStride, bigEndian)
 	case *ResultArg:
 		if a.Res == nil {
-			w.write(execArgConst)
-			w.write(a.Size())
-			w.write(a.Val)
-			w.write(0) // bit field offset
-			w.write(0) // bit field length
+			w.writeConstArg(a.Size(), a.Val, 0, 0, 0, false)
 		} else {
 			info, ok := w.args[a.Res]
 			if !ok {
@@ -285,11 +279,7 @@ func (w *execContext) writeArg(arg Arg, pid int) {
 			w.write(a.OpAdd)
 		}
 	case *PointerArg:
-		w.write(execArgConst)
-		w.write(a.Size())
-		w.write(w.target.physicalAddr(arg))
-		w.write(0) // bit field offset
-		w.write(0) // bit field length
+		w.writeConstArg(a.Size(), w.target.physicalAddr(arg), 0, 0, 0, false)
 	case *DataArg:
 		data := a.Data()
 		w.write(execArgData)
@@ -308,3 +298,13 @@ func (w *execContext) writeArg(arg Arg, pid int) {
 		panic("unknown arg type")
 	}
 }
+
+func (w *execContext) writeConstArg(size, val, bfOffset, bfLength, pidStride uint64, bigEndian bool) {
+	w.write(execArgConst)
+	meta := size | bfOffset<<16 | bfLength<<24 | pidStride<<32
+	if bigEndian {
+		meta |= 1 << 8
+	}
+	w.write(meta)
+	w.write(val)
+}
diff --git a/prog/encodingexec_test.go b/prog/encodingexec_test.go
index 15d58d87..5c2c1853 100644
--- a/prog/encodingexec_test.go
+++ b/prog/encodingexec_test.go
@@ -16,7 +16,7 @@ func TestSerializeForExecRandom(t *testing.T) {
 	buf := make([]byte, ExecBufferSize)
 	for i := 0; i < iters; i++ {
 		p := target.Generate(rs, 10, nil)
-		n, err := p.SerializeForExec(buf, i%16)
+		n, err := p.SerializeForExec(buf)
 		if err != nil {
 			t.Fatalf("failed to serialize: %v", err)
 		}
@@ -65,11 +65,11 @@ func TestSerializeForExec(t *testing.T) {
 			"syz_test$int(0x1, 0x2, 0x3, 0x4, 0x5)",
 			[]uint64{
 				callID("syz_test$int"), ExecNoCopyout, 5,
-				execArgConst, 8, 1, 0, 0,
-				execArgConst, 1, 2, 0, 0,
-				execArgConst, 2, 3, 0, 0,
-				execArgConst, 4, 4, 0, 0,
-				execArgConst, 8, 5, 0, 0,
+				execArgConst, 8, 1,
+				execArgConst, 1, 2,
+				execArgConst, 2, 3,
+				execArgConst, 4, 4,
+				execArgConst, 8, 5,
 				execInstrEOF,
 			},
 			nil,
@@ -77,12 +77,12 @@ func TestSerializeForExec(t *testing.T) {
 		{
 			"syz_test$align0(&(0x7f0000000000)={0x1, 0x2, 0x3, 0x4, 0x5})",
 			[]uint64{
-				execInstrCopyin, dataOffset + 0, execArgConst, 2, 1, 0, 0,
-				execInstrCopyin, dataOffset + 4, execArgConst, 4, 2, 0, 0,
-				execInstrCopyin, dataOffset + 8, execArgConst, 1, 3, 0, 0,
-				execInstrCopyin, dataOffset + 10, execArgConst, 2, 4, 0, 0,
-				execInstrCopyin, dataOffset + 16, execArgConst, 8, 5, 0, 0,
-				callID("syz_test$align0"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset, 0, 0,
+				execInstrCopyin, dataOffset + 0, execArgConst, 2, 1,
+				execInstrCopyin, dataOffset + 4, execArgConst, 4, 2,
+				execInstrCopyin, dataOffset + 8, execArgConst, 1, 3,
+				execInstrCopyin, dataOffset + 10, execArgConst, 2, 4,
+				execInstrCopyin, dataOffset + 16, execArgConst, 8, 5,
+				callID("syz_test$align0"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset,
 				execInstrEOF,
 			},
 			nil,
@@ -90,12 +90,12 @@ func TestSerializeForExec(t *testing.T) {
 		{
 			"syz_test$align1(&(0x7f0000000000)={0x1, 0x2, 0x3, 0x4, 0x5})",
 			[]uint64{
-				execInstrCopyin, dataOffset + 0, execArgConst, 2, 1, 0, 0,
-				execInstrCopyin, dataOffset + 2, execArgConst, 4, 2, 0, 0,
-				execInstrCopyin, dataOffset + 6, execArgConst, 1, 3, 0, 0,
-				execInstrCopyin, dataOffset + 7, execArgConst, 2, 4, 0, 0,
-				execInstrCopyin, dataOffset + 9, execArgConst, 8, 5, 0, 0,
-				callID("syz_test$align1"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset, 0, 0,
+				execInstrCopyin, dataOffset + 0, execArgConst, 2, 1,
+				execInstrCopyin, dataOffset + 2, execArgConst, 4, 2,
+				execInstrCopyin, dataOffset + 6, execArgConst, 1, 3,
+				execInstrCopyin, dataOffset + 7, execArgConst, 2, 4,
+				execInstrCopyin, dataOffset + 9, execArgConst, 8, 5,
+				callID("syz_test$align1"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset,
 				execInstrEOF,
 			},
 			nil,
@@ -103,10 +103,10 @@ func TestSerializeForExec(t *testing.T) {
 		{
 			"syz_test$align2(&(0x7f0000000000)={0x42, {[0x43]}, {[0x44]}})",
 			[]uint64{
-				execInstrCopyin, dataOffset + 0, execArgConst, 1, 0x42, 0, 0,
-				execInstrCopyin, dataOffset + 1, execArgConst, 2, 0x43, 0, 0,
-				execInstrCopyin, dataOffset + 4, execArgConst, 2, 0x44, 0, 0,
-				callID("syz_test$align2"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset, 0, 0,
+				execInstrCopyin, dataOffset + 0, execArgConst, 1, 0x42,
+				execInstrCopyin, dataOffset + 1, execArgConst, 2, 0x43,
+				execInstrCopyin, dataOffset + 4, execArgConst, 2, 0x44,
+				callID("syz_test$align2"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset,
 				execInstrEOF,
 			},
 			nil,
@@ -114,10 +114,10 @@ func TestSerializeForExec(t *testing.T) {
 		{
 			"syz_test$align3(&(0x7f0000000000)={0x42, {0x43}, {0x44}})",
 			[]uint64{
-				execInstrCopyin, dataOffset + 0, execArgConst, 1, 0x42, 0, 0,
-				execInstrCopyin, dataOffset + 1, execArgConst, 1, 0x43, 0, 0,
-				execInstrCopyin, dataOffset + 4, execArgConst, 1, 0x44, 0, 0,
-				callID("syz_test$align3"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset, 0, 0,
+				execInstrCopyin, dataOffset + 0, execArgConst, 1, 0x42,
+				execInstrCopyin, dataOffset + 1, execArgConst, 1, 0x43,
+				execInstrCopyin, dataOffset + 4, execArgConst, 1, 0x44,
+				callID("syz_test$align3"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset,
 				execInstrEOF,
 			},
 			nil,
@@ -125,10 +125,10 @@ func TestSerializeForExec(t *testing.T) {
 		{
 			"syz_test$align4(&(0x7f0000000000)={{0x42, 0x43}, 0x44})",
 			[]uint64{
-				execInstrCopyin, dataOffset + 0, execArgConst, 1, 0x42, 0, 0,
-				execInstrCopyin, dataOffset + 1, execArgConst, 2, 0x43, 0, 0,
-				execInstrCopyin, dataOffset + 4, execArgConst, 1, 0x44, 0, 0,
-				callID("syz_test$align4"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset, 0, 0,
+				execInstrCopyin, dataOffset + 0, execArgConst, 1, 0x42,
+				execInstrCopyin, dataOffset + 1, execArgConst, 2, 0x43,
+				execInstrCopyin, dataOffset + 4, execArgConst, 1, 0x44,
+				callID("syz_test$align4"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset,
 				execInstrEOF,
 			},
 			nil,
@@ -136,13 +136,13 @@ func TestSerializeForExec(t *testing.T) {
 		{
 			"syz_test$align5(&(0x7f0000000000)={{0x42, []}, {0x43, [0x44, 0x45, 0x46]}, 0x47})",
 			[]uint64{
-				execInstrCopyin, dataOffset + 0, execArgConst, 8, 0x42, 0, 0,
-				execInstrCopyin, dataOffset + 8, execArgConst, 8, 0x43, 0, 0,
-				execInstrCopyin, dataOffset + 16, execArgConst, 2, 0x44, 0, 0,
-				execInstrCopyin, dataOffset + 18, execArgConst, 2, 0x45, 0, 0,
-				execInstrCopyin, dataOffset + 20, execArgConst, 2, 0x46, 0, 0,
-				execInstrCopyin, dataOffset + 22, execArgConst, 1, 0x47, 0, 0,
-				callID("syz_test$align5"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset, 0, 0,
+				execInstrCopyin, dataOffset + 0, execArgConst, 8, 0x42,
+				execInstrCopyin, dataOffset + 8, execArgConst, 8, 0x43,
+				execInstrCopyin, dataOffset + 16, execArgConst, 2, 0x44,
+				execInstrCopyin, dataOffset + 18, execArgConst, 2, 0x45,
+				execInstrCopyin, dataOffset + 20, execArgConst, 2, 0x46,
+				execInstrCopyin, dataOffset + 22, execArgConst, 1, 0x47,
+				callID("syz_test$align5"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset,
 				execInstrEOF,
 			},
 			nil,
@@ -150,9 +150,9 @@ func TestSerializeForExec(t *testing.T) {
 		{
 			"syz_test$align6(&(0x7f0000000000)={0x42, [0x43]})",
 			[]uint64{
-				execInstrCopyin, dataOffset + 0, execArgConst, 1, 0x42, 0, 0,
-				execInstrCopyin, dataOffset + 4, execArgConst, 4, 0x43, 0, 0,
-				callID("syz_test$align6"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset, 0, 0,
+				execInstrCopyin, dataOffset + 0, execArgConst, 1, 0x42,
+				execInstrCopyin, dataOffset + 4, execArgConst, 4, 0x43,
+				callID("syz_test$align6"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset,
 				execInstrEOF,
 			},
 			nil,
@@ -160,9 +160,9 @@ func TestSerializeForExec(t *testing.T) {
 		{
 			"syz_test$union0(&(0x7f0000000000)={0x1, @f2=0x2})",
 			[]uint64{
-				execInstrCopyin, dataOffset + 0, execArgConst, 8, 1, 0, 0,
-				execInstrCopyin, dataOffset + 8, execArgConst, 1, 2, 0, 0,
-				callID("syz_test$union0"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset, 0, 0,
+				execInstrCopyin, dataOffset + 0, execArgConst, 8, 1,
+				execInstrCopyin, dataOffset + 8, execArgConst, 1, 2,
+				callID("syz_test$union0"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset,
 				execInstrEOF,
 			},
 			nil,
@@ -170,9 +170,9 @@ func TestSerializeForExec(t *testing.T) {
 		{
 			"syz_test$union1(&(0x7f0000000000)={@f1=0x42, 0x43})",
 			[]uint64{
-				execInstrCopyin, dataOffset + 0, execArgConst, 4, 0x42, 0, 0,
-				execInstrCopyin, dataOffset + 8, execArgConst, 1, 0x43, 0, 0,
-				callID("syz_test$union1"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset, 0, 0,
+				execInstrCopyin, dataOffset + 0, execArgConst, 4, 0x42,
+				execInstrCopyin, dataOffset + 8, execArgConst, 1, 0x43,
+				callID("syz_test$union1"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset,
 				execInstrEOF,
 			},
 			nil,
@@ -180,9 +180,9 @@ func TestSerializeForExec(t *testing.T) {
 		{
 			"syz_test$union2(&(0x7f0000000000)={@f1=0x42, 0x43})",
 			[]uint64{
-				execInstrCopyin, dataOffset + 0, execArgConst, 4, 0x42, 0, 0,
-				execInstrCopyin, dataOffset + 4, execArgConst, 1, 0x43, 0, 0,
-				callID("syz_test$union2"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset, 0, 0,
+				execInstrCopyin, dataOffset + 0, execArgConst, 4, 0x42,
+				execInstrCopyin, dataOffset + 4, execArgConst, 1, 0x43,
+				callID("syz_test$union2"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset,
 				execInstrEOF,
 			},
 			nil,
@@ -190,11 +190,11 @@ func TestSerializeForExec(t *testing.T) {
 		{
 			"syz_test$array0(&(0x7f0000000000)={0x1, [@f0=0x2, @f1=0x3], 0x4})",
 			[]uint64{
-				execInstrCopyin, dataOffset + 0, execArgConst, 1, 1, 0, 0,
-				execInstrCopyin, dataOffset + 1, execArgConst, 2, 2, 0, 0,
-				execInstrCopyin, dataOffset + 3, execArgConst, 8, 3, 0, 0,
-				execInstrCopyin, dataOffset + 11, execArgConst, 8, 4, 0, 0,
-				callID("syz_test$array0"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset, 0, 0,
+				execInstrCopyin, dataOffset + 0, execArgConst, 1, 1,
+				execInstrCopyin, dataOffset + 1, execArgConst, 2, 2,
+				execInstrCopyin, dataOffset + 3, execArgConst, 8, 3,
+				execInstrCopyin, dataOffset + 11, execArgConst, 8, 4,
+				callID("syz_test$array0"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset,
 				execInstrEOF,
 			},
 			nil,
@@ -202,9 +202,9 @@ func TestSerializeForExec(t *testing.T) {
 		{
 			"syz_test$array1(&(0x7f0000000000)={0x42, \"0102030405\"})",
 			[]uint64{
-				execInstrCopyin, dataOffset + 0, execArgConst, 1, 0x42, 0, 0,
+				execInstrCopyin, dataOffset + 0, execArgConst, 1, 0x42,
 				execInstrCopyin, dataOffset + 1, execArgData, 5, 0x0504030201,
-				callID("syz_test$array1"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset, 0, 0,
+				callID("syz_test$array1"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset,
 				execInstrEOF,
 			},
 			nil,
@@ -212,10 +212,10 @@ func TestSerializeForExec(t *testing.T) {
 		{
 			"syz_test$array2(&(0x7f0000000000)={0x42, \"aaaaaaaabbbbbbbbccccccccdddddddd\", 0x43})",
 			[]uint64{
-				execInstrCopyin, dataOffset + 0, execArgConst, 2, 0x42, 0, 0,
+				execInstrCopyin, dataOffset + 0, execArgConst, 2, 0x42,
 				execInstrCopyin, dataOffset + 2, execArgData, 16, 0xbbbbbbbbaaaaaaaa, 0xddddddddcccccccc,
-				execInstrCopyin, dataOffset + 18, execArgConst, 2, 0x43, 0, 0,
-				callID("syz_test$array2"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset, 0, 0,
+				execInstrCopyin, dataOffset + 18, execArgConst, 2, 0x43,
+				callID("syz_test$array2"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset,
 				execInstrEOF,
 			},
 			nil,
@@ -223,11 +223,11 @@ func TestSerializeForExec(t *testing.T) {
 		{
 			"syz_test$end0(&(0x7f0000000000)={0x42, 0x42, 0x42, 0x42})",
 			[]uint64{
-				execInstrCopyin, dataOffset + 0, execArgConst, 1, 0x42, 0, 0,
-				execInstrCopyin, dataOffset + 1, execArgConst, 2, 0x4200, 0, 0,
-				execInstrCopyin, dataOffset + 3, execArgConst, 4, 0x42000000, 0, 0,
-				execInstrCopyin, dataOffset + 7, execArgConst, 8, 0x4200000000000000, 0, 0,
-				callID("syz_test$end0"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset, 0, 0,
+				execInstrCopyin, dataOffset + 0, execArgConst, 1, 0x42,
+				execInstrCopyin, dataOffset + 1, execArgConst, 2 | 1<<8, 0x42,
+				execInstrCopyin, dataOffset + 3, execArgConst, 4 | 1<<8, 0x42,
+				execInstrCopyin, dataOffset + 7, execArgConst, 8 | 1<<8, 0x42,
+				callID("syz_test$end0"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset,
 				execInstrEOF,
 			},
 			nil,
@@ -235,10 +235,10 @@ func TestSerializeForExec(t *testing.T) {
 		{
 			"syz_test$end1(&(0x7f0000000000)={0xe, 0x42, 0x1})",
 			[]uint64{
-				execInstrCopyin, dataOffset + 0, execArgConst, 2, 0x0e00, 0, 0,
-				execInstrCopyin, dataOffset + 2, execArgConst, 4, 0x42000000, 0, 0,
-				execInstrCopyin, dataOffset + 6, execArgConst, 8, 0x0100000000000000, 0, 0,
-				callID("syz_test$end1"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset, 0, 0,
+				execInstrCopyin, dataOffset + 0, execArgConst, 2 | 1<<8, 0xe,
+				execInstrCopyin, dataOffset + 2, execArgConst, 4 | 1<<8, 0x42,
+				execInstrCopyin, dataOffset + 6, execArgConst, 8 | 1<<8, 0x1,
+				callID("syz_test$end1"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset,
 				execInstrEOF,
 			},
 			nil,
@@ -246,27 +246,112 @@ func TestSerializeForExec(t *testing.T) {
 		{
 			"syz_test$bf0(&(0x7f0000000000)={0x42, 0x42, 0x42, 0x42, 0x42, 0x42, 0x42, 0x42})",
 			[]uint64{
-				execInstrCopyin, dataOffset + 0, execArgConst, 2, 0x42, 0, 10,
-				execInstrCopyin, dataOffset + 8, execArgConst, 8, 0x42, 0, 0,
-				execInstrCopyin, dataOffset + 16, execArgConst, 2, 0x42, 0, 5,
-				execInstrCopyin, dataOffset + 16, execArgConst, 2, 0x42, 5, 6,
-				execInstrCopyin, dataOffset + 20, execArgConst, 4, 0x42, 0, 15,
-				execInstrCopyin, dataOffset + 24, execArgConst, 2, 0x42, 0, 11,
-				execInstrCopyin, dataOffset + 26, execArgConst, 2, 0x4200, 0, 11,
-				execInstrCopyin, dataOffset + 28, execArgConst, 1, 0x42, 0, 0,
-				callID("syz_test$bf0"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset, 0, 0,
+				execInstrCopyin, dataOffset + 0, execArgConst, 2 | 0<<16 | 10<<24, 0x42,
+				execInstrCopyin, dataOffset + 8, execArgConst, 8, 0x42,
+				execInstrCopyin, dataOffset + 16, execArgConst, 2 | 0<<16 | 5<<24, 0x42,
+				execInstrCopyin, dataOffset + 16, execArgConst, 2 | 5<<16 | 6<<24, 0x42,
+				execInstrCopyin, dataOffset + 20, execArgConst, 4 | 0<<16 | 15<<24, 0x42,
+				execInstrCopyin, dataOffset + 24, execArgConst, 2 | 0<<16 | 11<<24, 0x42,
+				execInstrCopyin, dataOffset + 26, execArgConst, 2 | 1<<8 | 0<<16 | 11<<24, 0x42,
+				execInstrCopyin, dataOffset + 28, execArgConst, 1, 0x42,
+				callID("syz_test$bf0"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset,
 				execInstrEOF,
 			},
-			nil,
+			&ExecProg{
+				Calls: []ExecCall{
+					{
+						Meta:  target.SyscallMap["syz_test$bf0"],
+						Index: ExecNoCopyout,
+						Args: []ExecArg{
+							ExecArgConst{
+								Size:  ptrSize,
+								Value: dataOffset,
+							},
+						},
+						Copyin: []ExecCopyin{
+							{
+								Addr: dataOffset + 0,
+								Arg: ExecArgConst{
+									Size:           2,
+									Value:          0x42,
+									BitfieldOffset: 0,
+									BitfieldLength: 10,
+								},
+							},
+							{
+								Addr: dataOffset + 8,
+								Arg: ExecArgConst{
+									Size:  8,
+									Value: 0x42,
+								},
+							},
+							{
+								Addr: dataOffset + 16,
+								Arg: ExecArgConst{
+									Size:           2,
+									Value:          0x42,
+									BitfieldOffset: 0,
+									BitfieldLength: 5,
+								},
+							},
+							{
+								Addr: dataOffset + 16,
+								Arg: ExecArgConst{
+									Size:           2,
+									Value:          0x42,
+									BitfieldOffset: 5,
+									BitfieldLength: 6,
+								},
+							},
+							{
+								Addr: dataOffset + 20,
+								Arg: ExecArgConst{
+									Size:           4,
+									Value:          0x42,
+									BitfieldOffset: 0,
+									BitfieldLength: 15,
+								},
+							},
+							{
+								Addr: dataOffset + 24,
+								Arg: ExecArgConst{
+									Size:           2,
+									Value:          0x42,
+									BitfieldOffset: 0,
+									BitfieldLength: 11,
+								},
+							},
+							{
+								Addr: dataOffset + 26,
+								Arg: ExecArgConst{
+									Size:           2,
+									Value:          0x42,
+									BitfieldOffset: 0,
+									BitfieldLength: 11,
+									BigEndian:      true,
+								},
+							},
+							{
+								Addr: dataOffset + 28,
+								Arg: ExecArgConst{
+									Size:  1,
+									Value: 0x42,
+								},
+							},
+						},
+					},
+				},
+				NumVars: 0,
+			},
 		},
 		{
 			"syz_test$bf1(&(0x7f0000000000)={{0x42, 0x42, 0x42}, 0x42})",
 			[]uint64{
-				execInstrCopyin, dataOffset + 0, execArgConst, 4, 0x42, 0, 10,
-				execInstrCopyin, dataOffset + 0, execArgConst, 4, 0x42, 10, 10,
-				execInstrCopyin, dataOffset + 0, execArgConst, 4, 0x42, 20, 10,
-				execInstrCopyin, dataOffset + 4, execArgConst, 1, 0x42, 0, 0,
-				callID("syz_test$bf1"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset, 0, 0,
+				execInstrCopyin, dataOffset + 0, execArgConst, 4 | 0<<16 | 10<<24, 0x42,
+				execInstrCopyin, dataOffset + 0, execArgConst, 4 | 10<<16 | 10<<24, 0x42,
+				execInstrCopyin, dataOffset + 0, execArgConst, 4 | 20<<16 | 10<<24, 0x42,
+				execInstrCopyin, dataOffset + 4, execArgConst, 1, 0x42,
+				callID("syz_test$bf1"), ExecNoCopyout, 1, execArgConst, ptrSize, dataOffset,
 				execInstrEOF,
 			},
 			nil,
@@ -274,7 +359,7 @@ func TestSerializeForExec(t *testing.T) {
 		{
 			"syz_test$res1(0xffff)",
 			[]uint64{
-				callID("syz_test$res1"), ExecNoCopyout, 1, execArgConst, 4, 0xffff, 0, 0,
+				callID("syz_test$res1"), ExecNoCopyout, 1, execArgConst, 4, 0xffff,
 				execInstrEOF,
 			},
 			nil,
@@ -289,7 +374,7 @@ func TestSerializeForExec(t *testing.T) {
 			if err != nil {
 				t.Fatalf("failed to deserialize prog %v: %v", i, err)
 			}
-			n, err := p.SerializeForExec(buf, i%16)
+			n, err := p.SerializeForExec(buf)
 			if err != nil {
 				t.Fatalf("failed to serialize: %v", err)
 			}
diff --git a/prog/prog.go b/prog/prog.go
index f78aac58..4a612d9b 100644
--- a/prog/prog.go
+++ b/prog/prog.go
@@ -63,31 +63,28 @@ func (arg *ConstArg) Size() uint64 {
 	return arg.typ.Size()
 }
 
-// Returns value taking endianness and executor pid into consideration.
-func (arg *ConstArg) Value(pid int) uint64 {
+// Value returns value, pid stride and endianness.
+func (arg *ConstArg) Value() (uint64, uint64, bool) {
 	switch typ := (*arg).Type().(type) {
 	case *IntType:
-		return encodeValue(arg.Val, typ.Size(), typ.BigEndian)
+		return arg.Val, 0, typ.BigEndian
 	case *ConstType:
-		return encodeValue(arg.Val, typ.Size(), typ.BigEndian)
+		return arg.Val, 0, typ.BigEndian
 	case *FlagsType:
-		return encodeValue(arg.Val, typ.Size(), typ.BigEndian)
+		return arg.Val, 0, typ.BigEndian
 	case *LenType:
-		return encodeValue(arg.Val, typ.Size(), typ.BigEndian)
+		return arg.Val, 0, typ.BigEndian
 	case *CsumType:
 		// Checksums are computed dynamically in executor.
-		return 0
+		return 0, 0, false
 	case *ResourceType:
-		if t, ok := typ.Desc.Type.(*IntType); ok {
-			return encodeValue(arg.Val, t.Size(), t.BigEndian)
-		} else {
-			panic(fmt.Sprintf("bad base type for a resource: %v", t))
-		}
+		t := typ.Desc.Type.(*IntType)
+		return arg.Val, 0, t.BigEndian
 	case *ProcType:
-		val := typ.ValuesStart + typ.ValuesPerProc*uint64(pid) + arg.Val
-		return encodeValue(val, typ.Size(), typ.BigEndian)
+		return typ.ValuesStart + arg.Val, typ.ValuesPerProc, typ.BigEndian
+	default:
+		panic(fmt.Sprintf("unknown ConstArg type %#v", typ))
 	}
-	return arg.Val
 }
 
 // Used for PtrType and VmaType.
@@ -281,22 +278,6 @@ func InnerArg(arg Arg) Arg {
 	return arg // Not a pointer.
 }
 
-func encodeValue(value uint64, size uint64, bigEndian bool) uint64 {
-	if !bigEndian {
-		return value
-	}
-	switch size {
-	case 2:
-		return uint64(swap16(uint16(value)))
-	case 4:
-		return uint64(swap32(uint32(value)))
-	case 8:
-		return swap64(value)
-	default:
-		panic(fmt.Sprintf("bad size %v for value %v", size, value))
-	}
-}
-
 func defaultArg(t Type) Arg {
 	switch typ := t.(type) {
 	case *IntType, *ConstType, *FlagsType, *LenType, *ProcType, *CsumType: