Makefile: don't compile all targets into target binaries

Currently target binaries contain support for all OS/arch combinations.
However, obviously a fuchsia target binary won't test windows.
For target binaries we need support only for a single target
(with the exception of 386/arm target in amd64/arm64 binaries).
So compile in only _the_ target into target binaries.
This reduces akaros/amd64 fuzzer binary from 33 to 7 MB
and execprog from 28 to 2 MB.

32 files changed, 152 insertions, 84 deletions

diff --git a/sys/akaros/gen/amd64.go b/sys/akaros/gen/amd64.go
index 252c10872..2ea6c588a 100644
--- a/sys/akaros/gen/amd64.go
+++ b/sys/akaros/gen/amd64.go
@@ -1,10 +1,14 @@
 // AUTOGENERATED FILE
+// +build !syz_target syz_target,syz_os_akaros,syz_arch_amd64
 
 package gen
 
 import . "github.com/google/syzkaller/prog"
+import . "github.com/google/syzkaller/sys/akaros"
 
-var Target_amd64 = &Target{OS: "akaros", Arch: "amd64", Revision: revision_amd64, PtrSize: 8, PageSize: 4096, NumPages: 4096, DataOffset: 536870912, Syscalls: syscalls_amd64, Resources: resources_amd64, Structs: structDescs_amd64, Consts: consts_amd64}
+func init() {
+	RegisterTarget(&Target{OS: "akaros", Arch: "amd64", Revision: revision_amd64, PtrSize: 8, PageSize: 4096, NumPages: 4096, DataOffset: 536870912, Syscalls: syscalls_amd64, Resources: resources_amd64, Structs: structDescs_amd64, Consts: consts_amd64}, InitTarget)
+}
 
 var resources_amd64 = []*ResourceDesc{
 	{Name: "fd", Type: &IntType{IntTypeCommon: IntTypeCommon{TypeCommon: TypeCommon{TypeName: "int32", TypeSize: 4}}}, Kind: []string{"fd"}, Values: []uint64{18446744073709551615, 18446744073709551516}},
@@ -1536,4 +1540,4 @@ var consts_amd64 = []ConstValue{
 	{Name: "WUNTRACED", Value: 2},
 }
 
-const revision_amd64 = "36f0e5da1becfe451b2936a2b8b1739deb53c609"
+const revision_amd64 = "0dd50d0ed02c0d84fb296a804d96c2f758c18e11"
diff --git a/sys/akaros/gen/empty.go b/sys/akaros/gen/empty.go
new file mode 100644
index 000000000..5baff07bf
--- /dev/null
+++ b/sys/akaros/gen/empty.go
@@ -0,0 +1,3 @@
+// AUTOGENERATED FILE
+// This file is needed if OS is completely excluded by build tags.
+package gen
diff --git a/sys/akaros/init.go b/sys/akaros/init.go
index c3b9e521a..91e1345a7 100644
--- a/sys/akaros/init.go
+++ b/sys/akaros/init.go
@@ -5,19 +5,14 @@ package akaros
 
 import (
 	"github.com/google/syzkaller/prog"
-	"github.com/google/syzkaller/sys/akaros/gen"
 	"github.com/google/syzkaller/sys/targets"
 )
 
-func init() {
-	prog.RegisterTarget(gen.Target_amd64, initTarget)
-}
-
 type arch struct {
 	unix *targets.UnixSanitizer
 }
 
-func initTarget(target *prog.Target) {
+func InitTarget(target *prog.Target) {
 	arch := &arch{
 		unix: targets.MakeUnixSanitizer(target),
 	}
diff --git a/sys/freebsd/gen/amd64.go b/sys/freebsd/gen/amd64.go
index ebfce0725..192053c73 100644
--- a/sys/freebsd/gen/amd64.go
+++ b/sys/freebsd/gen/amd64.go
@@ -1,10 +1,14 @@
 // AUTOGENERATED FILE
+// +build !syz_target syz_target,syz_os_freebsd,syz_arch_amd64
 
 package gen
 
 import . "github.com/google/syzkaller/prog"
+import . "github.com/google/syzkaller/sys/freebsd"
 
-var Target_amd64 = &Target{OS: "freebsd", Arch: "amd64", Revision: revision_amd64, PtrSize: 8, PageSize: 4096, NumPages: 4096, DataOffset: 536870912, Syscalls: syscalls_amd64, Resources: resources_amd64, Structs: structDescs_amd64, Consts: consts_amd64}
+func init() {
+	RegisterTarget(&Target{OS: "freebsd", Arch: "amd64", Revision: revision_amd64, PtrSize: 8, PageSize: 4096, NumPages: 4096, DataOffset: 536870912, Syscalls: syscalls_amd64, Resources: resources_amd64, Structs: structDescs_amd64, Consts: consts_amd64}, InitTarget)
+}
 
 var resources_amd64 = []*ResourceDesc{
 	{Name: "fd", Type: &IntType{IntTypeCommon: IntTypeCommon{TypeCommon: TypeCommon{TypeName: "int32", TypeSize: 4}}}, Kind: []string{"fd"}, Values: []uint64{18446744073709551615, 18446744073709551516}},
@@ -2439,4 +2443,4 @@ var consts_amd64 = []ConstValue{
 	{Name: "WUNTRACED", Value: 2},
 }
 
-const revision_amd64 = "fd7de83a3ebf8e454b041bbfe7513ed4a139d44d"
+const revision_amd64 = "89eac40a68a14ffc0af9fc9b181147236b82d00b"
diff --git a/sys/freebsd/gen/empty.go b/sys/freebsd/gen/empty.go
new file mode 100644
index 000000000..5baff07bf
--- /dev/null
+++ b/sys/freebsd/gen/empty.go
@@ -0,0 +1,3 @@
+// AUTOGENERATED FILE
+// This file is needed if OS is completely excluded by build tags.
+package gen
diff --git a/sys/freebsd/init.go b/sys/freebsd/init.go
index f75fb5d97..ab2224715 100644
--- a/sys/freebsd/init.go
+++ b/sys/freebsd/init.go
@@ -5,15 +5,10 @@ package freebsd
 
 import (
 	"github.com/google/syzkaller/prog"
-	"github.com/google/syzkaller/sys/freebsd/gen"
 	"github.com/google/syzkaller/sys/targets"
 )
 
-func init() {
-	prog.RegisterTarget(gen.Target_amd64, initTarget)
-}
-
-func initTarget(target *prog.Target) {
+func InitTarget(target *prog.Target) {
 	arch := &arch{
 		unix: targets.MakeUnixSanitizer(target),
 	}
diff --git a/sys/fuchsia/gen/amd64.go b/sys/fuchsia/gen/amd64.go
index 63d7a8ff2..8e91dd584 100644
--- a/sys/fuchsia/gen/amd64.go
+++ b/sys/fuchsia/gen/amd64.go
@@ -1,10 +1,14 @@
 // AUTOGENERATED FILE
+// +build !syz_target syz_target,syz_os_fuchsia,syz_arch_amd64
 
 package gen
 
 import . "github.com/google/syzkaller/prog"
+import . "github.com/google/syzkaller/sys/fuchsia"
 
-var Target_amd64 = &Target{OS: "fuchsia", Arch: "amd64", Revision: revision_amd64, PtrSize: 8, PageSize: 4096, NumPages: 4096, DataOffset: 536870912, Syscalls: syscalls_amd64, Resources: resources_amd64, Structs: structDescs_amd64, Consts: consts_amd64}
+func init() {
+	RegisterTarget(&Target{OS: "fuchsia", Arch: "amd64", Revision: revision_amd64, PtrSize: 8, PageSize: 4096, NumPages: 4096, DataOffset: 536870912, Syscalls: syscalls_amd64, Resources: resources_amd64, Structs: structDescs_amd64, Consts: consts_amd64}, InitTarget)
+}
 
 var resources_amd64 = []*ResourceDesc{
 	{Name: "fd", Type: &IntType{IntTypeCommon: IntTypeCommon{TypeCommon: TypeCommon{TypeName: "int32", TypeSize: 4}}}, Kind: []string{"fd"}, Values: []uint64{18446744073709551615, 18446744073709551516}},
@@ -1317,4 +1321,4 @@ var consts_amd64 = []ConstValue{
 	{Name: "ZX_WAIT_ASYNC_REPEATING", Value: 1},
 }
 
-const revision_amd64 = "9540132f74bbe9bfb7e8f215844bdb3a88b9a665"
+const revision_amd64 = "4cc56cb437136b65655dd3e0d9389be66131c7d1"
diff --git a/sys/fuchsia/gen/arm64.go b/sys/fuchsia/gen/arm64.go
index 326d53079..69bc14651 100644
--- a/sys/fuchsia/gen/arm64.go
+++ b/sys/fuchsia/gen/arm64.go
@@ -1,10 +1,14 @@
 // AUTOGENERATED FILE
+// +build !syz_target syz_target,syz_os_fuchsia,syz_arch_arm64
 
 package gen
 
 import . "github.com/google/syzkaller/prog"
+import . "github.com/google/syzkaller/sys/fuchsia"
 
-var Target_arm64 = &Target{OS: "fuchsia", Arch: "arm64", Revision: revision_arm64, PtrSize: 8, PageSize: 4096, NumPages: 4096, DataOffset: 536870912, Syscalls: syscalls_arm64, Resources: resources_arm64, Structs: structDescs_arm64, Consts: consts_arm64}
+func init() {
+	RegisterTarget(&Target{OS: "fuchsia", Arch: "arm64", Revision: revision_arm64, PtrSize: 8, PageSize: 4096, NumPages: 4096, DataOffset: 536870912, Syscalls: syscalls_arm64, Resources: resources_arm64, Structs: structDescs_arm64, Consts: consts_arm64}, InitTarget)
+}
 
 var resources_arm64 = []*ResourceDesc{
 	{Name: "fd", Type: &IntType{IntTypeCommon: IntTypeCommon{TypeCommon: TypeCommon{TypeName: "int32", TypeSize: 4}}}, Kind: []string{"fd"}, Values: []uint64{18446744073709551615, 18446744073709551516}},
@@ -1317,4 +1321,4 @@ var consts_arm64 = []ConstValue{
 	{Name: "ZX_WAIT_ASYNC_REPEATING", Value: 1},
 }
 
-const revision_arm64 = "ebb425942f2bbfd2db293e4a2a0a417f6aaafb1c"
+const revision_arm64 = "42ba25aa193b27b48c8f8ade1c9186cb89c7ca61"
diff --git a/sys/fuchsia/gen/empty.go b/sys/fuchsia/gen/empty.go
new file mode 100644
index 000000000..5baff07bf
--- /dev/null
+++ b/sys/fuchsia/gen/empty.go
@@ -0,0 +1,3 @@
+// AUTOGENERATED FILE
+// This file is needed if OS is completely excluded by build tags.
+package gen
diff --git a/sys/fuchsia/init.go b/sys/fuchsia/init.go
index 3f02e151d..eefba3950 100644
--- a/sys/fuchsia/init.go
+++ b/sys/fuchsia/init.go
@@ -5,15 +5,9 @@ package fuchsia
 
 import (
 	"github.com/google/syzkaller/prog"
-	"github.com/google/syzkaller/sys/fuchsia/gen"
 	"github.com/google/syzkaller/sys/targets"
 )
 
-func init() {
-	prog.RegisterTarget(gen.Target_amd64, initTarget)
-	prog.RegisterTarget(gen.Target_arm64, initTarget)
-}
-
-func initTarget(target *prog.Target) {
+func InitTarget(target *prog.Target) {
 	target.MakeMmap = targets.MakeSyzMmap(target)
 }
diff --git a/sys/linux/gen/386.go b/sys/linux/gen/386.go
index 972193818..82bb7aa81 100644
--- a/sys/linux/gen/386.go
+++ b/sys/linux/gen/386.go
@@ -1,10 +1,14 @@
 // AUTOGENERATED FILE
+// +build !syz_target syz_target,syz_os_linux,syz_arch_386 syz_target,syz_os_linux,syz_arch_amd64
 
 package gen
 
 import . "github.com/google/syzkaller/prog"
+import . "github.com/google/syzkaller/sys/linux"
 
-var Target_386 = &Target{OS: "linux", Arch: "386", Revision: revision_386, PtrSize: 4, PageSize: 4096, NumPages: 4096, DataOffset: 536870912, Syscalls: syscalls_386, Resources: resources_386, Structs: structDescs_386, Consts: consts_386}
+func init() {
+	RegisterTarget(&Target{OS: "linux", Arch: "386", Revision: revision_386, PtrSize: 4, PageSize: 4096, NumPages: 4096, DataOffset: 536870912, Syscalls: syscalls_386, Resources: resources_386, Structs: structDescs_386, Consts: consts_386}, InitTarget)
+}
 
 var resources_386 = []*ResourceDesc{
 	{Name: "assoc_id", Type: &IntType{IntTypeCommon: IntTypeCommon{TypeCommon: TypeCommon{TypeName: "int32", TypeSize: 4}}}, Kind: []string{"assoc_id"}, Values: []uint64{0}},
@@ -39509,4 +39513,4 @@ var consts_386 = []ConstValue{
 	{Name: "bpf_insn_load_imm_dw", Value: 24},
 }
 
-const revision_386 = "d16df4bd3b5d63c53207d8d48f0e7aa8375ae471"
+const revision_386 = "c026c82f557e0fb27209b060f233071e8ba38eab"
diff --git a/sys/linux/gen/amd64.go b/sys/linux/gen/amd64.go
index 6fffdec69..c2747f266 100644
--- a/sys/linux/gen/amd64.go
+++ b/sys/linux/gen/amd64.go
@@ -1,10 +1,14 @@
 // AUTOGENERATED FILE
+// +build !syz_target syz_target,syz_os_linux,syz_arch_amd64
 
 package gen
 
 import . "github.com/google/syzkaller/prog"
+import . "github.com/google/syzkaller/sys/linux"
 
-var Target_amd64 = &Target{OS: "linux", Arch: "amd64", Revision: revision_amd64, PtrSize: 8, PageSize: 4096, NumPages: 4096, DataOffset: 536870912, Syscalls: syscalls_amd64, Resources: resources_amd64, Structs: structDescs_amd64, Consts: consts_amd64}
+func init() {
+	RegisterTarget(&Target{OS: "linux", Arch: "amd64", Revision: revision_amd64, PtrSize: 8, PageSize: 4096, NumPages: 4096, DataOffset: 536870912, Syscalls: syscalls_amd64, Resources: resources_amd64, Structs: structDescs_amd64, Consts: consts_amd64}, InitTarget)
+}
 
 var resources_amd64 = []*ResourceDesc{
 	{Name: "assoc_id", Type: &IntType{IntTypeCommon: IntTypeCommon{TypeCommon: TypeCommon{TypeName: "int32", TypeSize: 4}}}, Kind: []string{"assoc_id"}, Values: []uint64{0}},
@@ -40196,4 +40200,4 @@ var consts_amd64 = []ConstValue{
 	{Name: "bpf_insn_load_imm_dw", Value: 24},
 }
 
-const revision_amd64 = "22bac64bd4f91440dd851726a290b9eb1f1ae092"
+const revision_amd64 = "c06fc3bdc53ae8ee708128ddd51d14a679aa12f0"
diff --git a/sys/linux/gen/arm.go b/sys/linux/gen/arm.go
index 160738afd..8192e252a 100644
--- a/sys/linux/gen/arm.go
+++ b/sys/linux/gen/arm.go
@@ -1,10 +1,14 @@
 // AUTOGENERATED FILE
+// +build !syz_target syz_target,syz_os_linux,syz_arch_arm syz_target,syz_os_linux,syz_arch_arm64
 
 package gen
 
 import . "github.com/google/syzkaller/prog"
+import . "github.com/google/syzkaller/sys/linux"
 
-var Target_arm = &Target{OS: "linux", Arch: "arm", Revision: revision_arm, PtrSize: 4, PageSize: 4096, NumPages: 4096, DataOffset: 536870912, Syscalls: syscalls_arm, Resources: resources_arm, Structs: structDescs_arm, Consts: consts_arm}
+func init() {
+	RegisterTarget(&Target{OS: "linux", Arch: "arm", Revision: revision_arm, PtrSize: 4, PageSize: 4096, NumPages: 4096, DataOffset: 536870912, Syscalls: syscalls_arm, Resources: resources_arm, Structs: structDescs_arm, Consts: consts_arm}, InitTarget)
+}
 
 var resources_arm = []*ResourceDesc{
 	{Name: "assoc_id", Type: &IntType{IntTypeCommon: IntTypeCommon{TypeCommon: TypeCommon{TypeName: "int32", TypeSize: 4}}}, Kind: []string{"assoc_id"}, Values: []uint64{0}},
@@ -39367,4 +39371,4 @@ var consts_arm = []ConstValue{
 	{Name: "bpf_insn_load_imm_dw", Value: 24},
 }
 
-const revision_arm = "c46361b24a9d8c4d25f99c6a74ed373b73b0cdd1"
+const revision_arm = "b4f6cbe7c414a45bfaf3dcccf7f1040502de3980"
diff --git a/sys/linux/gen/arm64.go b/sys/linux/gen/arm64.go
index 8bf0d11df..d783efc8b 100644
--- a/sys/linux/gen/arm64.go
+++ b/sys/linux/gen/arm64.go
@@ -1,10 +1,14 @@
 // AUTOGENERATED FILE
+// +build !syz_target syz_target,syz_os_linux,syz_arch_arm64
 
 package gen
 
 import . "github.com/google/syzkaller/prog"
+import . "github.com/google/syzkaller/sys/linux"
 
-var Target_arm64 = &Target{OS: "linux", Arch: "arm64", Revision: revision_arm64, PtrSize: 8, PageSize: 4096, NumPages: 4096, DataOffset: 536870912, Syscalls: syscalls_arm64, Resources: resources_arm64, Structs: structDescs_arm64, Consts: consts_arm64}
+func init() {
+	RegisterTarget(&Target{OS: "linux", Arch: "arm64", Revision: revision_arm64, PtrSize: 8, PageSize: 4096, NumPages: 4096, DataOffset: 536870912, Syscalls: syscalls_arm64, Resources: resources_arm64, Structs: structDescs_arm64, Consts: consts_arm64}, InitTarget)
+}
 
 var resources_arm64 = []*ResourceDesc{
 	{Name: "assoc_id", Type: &IntType{IntTypeCommon: IntTypeCommon{TypeCommon: TypeCommon{TypeName: "int32", TypeSize: 4}}}, Kind: []string{"assoc_id"}, Values: []uint64{0}},
@@ -39561,4 +39565,4 @@ var consts_arm64 = []ConstValue{
 	{Name: "bpf_insn_load_imm_dw", Value: 24},
 }
 
-const revision_arm64 = "e1ce203bf0cb9e092e65fc6ca9cd1cde96e19316"
+const revision_arm64 = "70ff2aa900dc3911170ab814adc6a362bb014580"
diff --git a/sys/linux/gen/empty.go b/sys/linux/gen/empty.go
new file mode 100644
index 000000000..5baff07bf
--- /dev/null
+++ b/sys/linux/gen/empty.go
@@ -0,0 +1,3 @@
+// AUTOGENERATED FILE
+// This file is needed if OS is completely excluded by build tags.
+package gen
diff --git a/sys/linux/gen/ppc64le.go b/sys/linux/gen/ppc64le.go
index d8f088418..8ffa0b43f 100644
--- a/sys/linux/gen/ppc64le.go
+++ b/sys/linux/gen/ppc64le.go
@@ -1,10 +1,14 @@
 // AUTOGENERATED FILE
+// +build !syz_target syz_target,syz_os_linux,syz_arch_ppc64le
 
 package gen
 
 import . "github.com/google/syzkaller/prog"
+import . "github.com/google/syzkaller/sys/linux"
 
-var Target_ppc64le = &Target{OS: "linux", Arch: "ppc64le", Revision: revision_ppc64le, PtrSize: 8, PageSize: 4096, NumPages: 4096, DataOffset: 536870912, Syscalls: syscalls_ppc64le, Resources: resources_ppc64le, Structs: structDescs_ppc64le, Consts: consts_ppc64le}
+func init() {
+	RegisterTarget(&Target{OS: "linux", Arch: "ppc64le", Revision: revision_ppc64le, PtrSize: 8, PageSize: 4096, NumPages: 4096, DataOffset: 536870912, Syscalls: syscalls_ppc64le, Resources: resources_ppc64le, Structs: structDescs_ppc64le, Consts: consts_ppc64le}, InitTarget)
+}
 
 var resources_ppc64le = []*ResourceDesc{
 	{Name: "assoc_id", Type: &IntType{IntTypeCommon: IntTypeCommon{TypeCommon: TypeCommon{TypeName: "int32", TypeSize: 4}}}, Kind: []string{"assoc_id"}, Values: []uint64{0}},
@@ -36992,4 +36996,4 @@ var consts_ppc64le = []ConstValue{
 	{Name: "bpf_insn_load_imm_dw", Value: 24},
 }
 
-const revision_ppc64le = "1ccba534d5c6adaffc5ebfbea33c22833f5cb846"
+const revision_ppc64le = "be0af9fd447e9ac157423f3260f414d60066f653"
diff --git a/sys/linux/init.go b/sys/linux/init.go
index 8d7231fcd..035ffee2f 100644
--- a/sys/linux/init.go
+++ b/sys/linux/init.go
@@ -7,10 +7,10 @@ import (
 	"runtime"
 
 	"github.com/google/syzkaller/prog"
-	"github.com/google/syzkaller/sys/linux/gen"
 	"github.com/google/syzkaller/sys/targets"
 )
 
+/*
 func init() {
 	prog.RegisterTarget(gen.Target_amd64, initTarget)
 	prog.RegisterTarget(gen.Target_386, initTarget)
@@ -18,8 +18,9 @@ func init() {
 	prog.RegisterTarget(gen.Target_arm, initTarget)
 	prog.RegisterTarget(gen.Target_ppc64le, initTarget)
 }
+*/
 
-func initTarget(target *prog.Target) {
+func InitTarget(target *prog.Target) {
 	arch := &arch{
 		unix:                      targets.MakeUnixSanitizer(target),
 		clockGettimeSyscall:       target.SyscallMap["clock_gettime"],
diff --git a/sys/netbsd/gen/amd64.go b/sys/netbsd/gen/amd64.go
index be9bbb998..cd7cdcd03 100644
--- a/sys/netbsd/gen/amd64.go
+++ b/sys/netbsd/gen/amd64.go
@@ -1,10 +1,14 @@
 // AUTOGENERATED FILE
+// +build !syz_target syz_target,syz_os_netbsd,syz_arch_amd64
 
 package gen
 
 import . "github.com/google/syzkaller/prog"
+import . "github.com/google/syzkaller/sys/netbsd"
 
-var Target_amd64 = &Target{OS: "netbsd", Arch: "amd64", Revision: revision_amd64, PtrSize: 8, PageSize: 4096, NumPages: 4096, DataOffset: 536870912, Syscalls: syscalls_amd64, Resources: resources_amd64, Structs: structDescs_amd64, Consts: consts_amd64}
+func init() {
+	RegisterTarget(&Target{OS: "netbsd", Arch: "amd64", Revision: revision_amd64, PtrSize: 8, PageSize: 4096, NumPages: 4096, DataOffset: 536870912, Syscalls: syscalls_amd64, Resources: resources_amd64, Structs: structDescs_amd64, Consts: consts_amd64}, InitTarget)
+}
 
 var resources_amd64 = []*ResourceDesc{
 	{Name: "fd", Type: &IntType{IntTypeCommon: IntTypeCommon{TypeCommon: TypeCommon{TypeName: "int32", TypeSize: 4}}}, Kind: []string{"fd"}, Values: []uint64{18446744073709551615, 18446744073709551516}},
@@ -1673,4 +1677,4 @@ var consts_amd64 = []ConstValue{
 	{Name: "WUNTRACED", Value: 2},
 }
 
-const revision_amd64 = "cea6c87ab1f9e36df1927913a619e71cd29abcbf"
+const revision_amd64 = "c05720ceb16e651f6ae9addd1f5be83497d861e3"
diff --git a/sys/netbsd/gen/empty.go b/sys/netbsd/gen/empty.go
new file mode 100644
index 000000000..5baff07bf
--- /dev/null
+++ b/sys/netbsd/gen/empty.go
@@ -0,0 +1,3 @@
+// AUTOGENERATED FILE
+// This file is needed if OS is completely excluded by build tags.
+package gen
diff --git a/sys/netbsd/init.go b/sys/netbsd/init.go
index 908cbe655..7b6b1250e 100644
--- a/sys/netbsd/init.go
+++ b/sys/netbsd/init.go
@@ -5,15 +5,10 @@ package netbsd
 
 import (
 	"github.com/google/syzkaller/prog"
-	"github.com/google/syzkaller/sys/netbsd/gen"
 	"github.com/google/syzkaller/sys/targets"
 )
 
-func init() {
-	prog.RegisterTarget(gen.Target_amd64, initTarget)
-}
-
-func initTarget(target *prog.Target) {
+func InitTarget(target *prog.Target) {
 	arch := &arch{
 		MAP_FIXED: target.ConstMap["MAP_FIXED"],
 	}
diff --git a/sys/sys.go b/sys/sys.go
index e67093e16..51c04b444 100644
--- a/sys/sys.go
+++ b/sys/sys.go
@@ -5,13 +5,13 @@ package sys
 
 import (
 	// Import all targets, so that users only need to import sys.
-	_ "github.com/google/syzkaller/sys/akaros"
-	_ "github.com/google/syzkaller/sys/freebsd"
-	_ "github.com/google/syzkaller/sys/fuchsia"
-	_ "github.com/google/syzkaller/sys/linux"
-	_ "github.com/google/syzkaller/sys/netbsd"
-	_ "github.com/google/syzkaller/sys/test"
-	_ "github.com/google/syzkaller/sys/windows"
+	_ "github.com/google/syzkaller/sys/akaros/gen"
+	_ "github.com/google/syzkaller/sys/freebsd/gen"
+	_ "github.com/google/syzkaller/sys/fuchsia/gen"
+	_ "github.com/google/syzkaller/sys/linux/gen"
+	_ "github.com/google/syzkaller/sys/netbsd/gen"
+	_ "github.com/google/syzkaller/sys/test/gen"
+	_ "github.com/google/syzkaller/sys/windows/gen"
 )
 
 // Emitted by Makefile.
diff --git a/sys/syz-sysgen/sysgen.go b/sys/syz-sysgen/sysgen.go
index 65242910b..467987c45 100644
--- a/sys/syz-sysgen/sysgen.go
+++ b/sys/syz-sysgen/sysgen.go
@@ -114,6 +114,7 @@ func main() {
 				job.OK = true
 			}()
 		}
+		writeEmpty(OS)
 		wg.Wait()
 
 		var syscallArchs []ArchData
@@ -160,15 +161,23 @@ func main() {
 }
 
 func generate(target *targets.Target, prg *compiler.Prog, consts map[string]uint64, out io.Writer) {
-	fmt.Fprintf(out, "// AUTOGENERATED FILE\n\n")
+	tag := fmt.Sprintf("syz_target,syz_os_%v,syz_arch_%v", target.OS, target.Arch)
+	if target.VMArch != "" {
+		tag += fmt.Sprintf(" syz_target,syz_os_%v,syz_arch_%v", target.OS, target.VMArch)
+	}
+	fmt.Fprintf(out, "// AUTOGENERATED FILE\n")
+	fmt.Fprintf(out, "// +build !syz_target %v\n\n", tag)
 	fmt.Fprintf(out, "package gen\n\n")
-	fmt.Fprintf(out, "import . \"github.com/google/syzkaller/prog\"\n\n")
+	fmt.Fprintf(out, "import . \"github.com/google/syzkaller/prog\"\n")
+	fmt.Fprintf(out, "import . \"github.com/google/syzkaller/sys/%v\"\n\n", target.OS)
 
-	fmt.Fprintf(out, "var Target_%v = &Target{"+
+	fmt.Fprintf(out, "func init() {\n")
+	fmt.Fprintf(out, "\tRegisterTarget(&Target{"+
 		"OS: %q, Arch: %q, Revision: revision_%v, PtrSize: %v, "+
 		"PageSize: %v, NumPages: %v, DataOffset: %v, Syscalls: syscalls_%v, "+
-		"Resources: resources_%v, Structs: structDescs_%v, Consts: consts_%v}\n\n",
-		target.Arch, target.OS, target.Arch, target.Arch, target.PtrSize,
+		"Resources: resources_%v, Structs: structDescs_%v, Consts: consts_%v}, "+
+		"InitTarget)\n}\n\n",
+		target.OS, target.Arch, target.Arch, target.PtrSize,
 		target.PageSize, target.NumPages, target.DataOffset,
 		target.Arch, target.Arch, target.Arch, target.Arch)
 
@@ -196,6 +205,14 @@ func generate(target *targets.Target, prg *compiler.Prog, consts map[string]uint
 	fmt.Fprintf(out, "\n\n")
 }
 
+func writeEmpty(OS string) {
+	const data = `// AUTOGENERATED FILE
+// This file is needed if OS is completely excluded by build tags.
+package gen
+`
+	writeSource(filepath.Join("sys", OS, "gen", "empty.go"), []byte(data))
+}
+
 func generateExecutorSyscalls(target *targets.Target, syscalls []*prog.Syscall, rev string) ArchData {
 	data := ArchData{
 		Revision:   rev,
diff --git a/sys/targets/targets.go b/sys/targets/targets.go
index 59220625c..ea742f14e 100644
--- a/sys/targets/targets.go
+++ b/sys/targets/targets.go
@@ -16,6 +16,7 @@ type Target struct {
 	osCommon
 	OS               string
 	Arch             string
+	VMArch           string // e.g. amd64 for 386, or arm64 for arm
 	PtrSize          uint64
 	PageSize         uint64
 	NumPages         uint64
@@ -123,6 +124,7 @@ var List = map[string]map[string]*Target{
 			},
 		},
 		"386": {
+			VMArch:           "amd64",
 			PtrSize:          4,
 			PageSize:         4 << 10,
 			CFlags:           []string{"-m32"},
@@ -140,6 +142,7 @@ var List = map[string]map[string]*Target{
 			KernelHeaderArch: "arm64",
 		},
 		"arm": {
+			VMArch:           "arm64",
 			PtrSize:          4,
 			PageSize:         4 << 10,
 			CFlags:           []string{"-D__LINUX_ARM_ARCH__=6", "-m32", "-D__ARM_EABI__"},
diff --git a/sys/test/gen/32_fork_shmem.go b/sys/test/gen/32_fork_shmem.go
index e9c5d42ee..b61c234c1 100644
--- a/sys/test/gen/32_fork_shmem.go
+++ b/sys/test/gen/32_fork_shmem.go
@@ -1,10 +1,14 @@
 // AUTOGENERATED FILE
+// +build !syz_target syz_target,syz_os_test,syz_arch_32_fork_shmem
 
 package gen
 
 import . "github.com/google/syzkaller/prog"
+import . "github.com/google/syzkaller/sys/test"
 
-var Target_32_fork_shmem = &Target{OS: "test", Arch: "32_fork_shmem", Revision: revision_32_fork_shmem, PtrSize: 4, PageSize: 4096, NumPages: 4096, DataOffset: 536870912, Syscalls: syscalls_32_fork_shmem, Resources: resources_32_fork_shmem, Structs: structDescs_32_fork_shmem, Consts: consts_32_fork_shmem}
+func init() {
+	RegisterTarget(&Target{OS: "test", Arch: "32_fork_shmem", Revision: revision_32_fork_shmem, PtrSize: 4, PageSize: 4096, NumPages: 4096, DataOffset: 536870912, Syscalls: syscalls_32_fork_shmem, Resources: resources_32_fork_shmem, Structs: structDescs_32_fork_shmem, Consts: consts_32_fork_shmem}, InitTarget)
+}
 
 var resources_32_fork_shmem = []*ResourceDesc(nil)
 
@@ -24,4 +28,4 @@ var consts_32_fork_shmem = []ConstValue{
 	{Name: "ONLY_32BITS_CONST", Value: 1},
 }
 
-const revision_32_fork_shmem = "f3f80dea03f2b372f892da4a49e6af7f47106120"
+const revision_32_fork_shmem = "18f983f4760ca5ac41eaf7c18bd9f487f6dde42b"
diff --git a/sys/test/gen/32_shmem.go b/sys/test/gen/32_shmem.go
index 39e2b9400..02db6010e 100644
--- a/sys/test/gen/32_shmem.go
+++ b/sys/test/gen/32_shmem.go
@@ -1,10 +1,14 @@
 // AUTOGENERATED FILE
+// +build !syz_target syz_target,syz_os_test,syz_arch_32_shmem
 
 package gen
 
 import . "github.com/google/syzkaller/prog"
+import . "github.com/google/syzkaller/sys/test"
 
-var Target_32_shmem = &Target{OS: "test", Arch: "32_shmem", Revision: revision_32_shmem, PtrSize: 4, PageSize: 8192, NumPages: 2048, DataOffset: 536870912, Syscalls: syscalls_32_shmem, Resources: resources_32_shmem, Structs: structDescs_32_shmem, Consts: consts_32_shmem}
+func init() {
+	RegisterTarget(&Target{OS: "test", Arch: "32_shmem", Revision: revision_32_shmem, PtrSize: 4, PageSize: 8192, NumPages: 2048, DataOffset: 536870912, Syscalls: syscalls_32_shmem, Resources: resources_32_shmem, Structs: structDescs_32_shmem, Consts: consts_32_shmem}, InitTarget)
+}
 
 var resources_32_shmem = []*ResourceDesc(nil)
 
@@ -24,4 +28,4 @@ var consts_32_shmem = []ConstValue{
 	{Name: "ONLY_32BITS_CONST", Value: 1},
 }
 
-const revision_32_shmem = "9819b8a5a8ea14bf3a71d86bb2012bafd6ab25b6"
+const revision_32_shmem = "9d4e8ff9d9c38d5fe7cdc046adcde8be29782e6b"
diff --git a/sys/test/gen/64.go b/sys/test/gen/64.go
index d1057117f..b594499c8 100644
--- a/sys/test/gen/64.go
+++ b/sys/test/gen/64.go
@@ -1,10 +1,14 @@
 // AUTOGENERATED FILE
+// +build !syz_target syz_target,syz_os_test,syz_arch_64
 
 package gen
 
 import . "github.com/google/syzkaller/prog"
+import . "github.com/google/syzkaller/sys/test"
 
-var Target_64 = &Target{OS: "test", Arch: "64", Revision: revision_64, PtrSize: 8, PageSize: 4096, NumPages: 4096, DataOffset: 536870912, Syscalls: syscalls_64, Resources: resources_64, Structs: structDescs_64, Consts: consts_64}
+func init() {
+	RegisterTarget(&Target{OS: "test", Arch: "64", Revision: revision_64, PtrSize: 8, PageSize: 4096, NumPages: 4096, DataOffset: 536870912, Syscalls: syscalls_64, Resources: resources_64, Structs: structDescs_64, Consts: consts_64}, InitTarget)
+}
 
 var resources_64 = []*ResourceDesc{
 	{Name: "anyres32", Type: &IntType{IntTypeCommon: IntTypeCommon{TypeCommon: TypeCommon{TypeName: "int32", TypeSize: 4}}}, Kind: []string{"anyres32"}, Values: []uint64{0}},
@@ -875,4 +879,4 @@ var consts_64 = []ConstValue{
 	{Name: "SYS_unsupported"},
 }
 
-const revision_64 = "96964f599c9870f5d27e4d6054b0d16011652c81"
+const revision_64 = "981444b6842c8896801fdf67dc75c454cad9e594"
diff --git a/sys/test/gen/64_fork.go b/sys/test/gen/64_fork.go
index 533715055..ca62e9ce0 100644
--- a/sys/test/gen/64_fork.go
+++ b/sys/test/gen/64_fork.go
@@ -1,10 +1,14 @@
 // AUTOGENERATED FILE
+// +build !syz_target syz_target,syz_os_test,syz_arch_64_fork
 
 package gen
 
 import . "github.com/google/syzkaller/prog"
+import . "github.com/google/syzkaller/sys/test"
 
-var Target_64_fork = &Target{OS: "test", Arch: "64_fork", Revision: revision_64_fork, PtrSize: 8, PageSize: 8192, NumPages: 2048, DataOffset: 536870912, Syscalls: syscalls_64_fork, Resources: resources_64_fork, Structs: structDescs_64_fork, Consts: consts_64_fork}
+func init() {
+	RegisterTarget(&Target{OS: "test", Arch: "64_fork", Revision: revision_64_fork, PtrSize: 8, PageSize: 8192, NumPages: 2048, DataOffset: 536870912, Syscalls: syscalls_64_fork, Resources: resources_64_fork, Structs: structDescs_64_fork, Consts: consts_64_fork}, InitTarget)
+}
 
 var resources_64_fork = []*ResourceDesc(nil)
 
@@ -23,4 +27,4 @@ var consts_64_fork = []ConstValue{
 	{Name: "IPPROTO_UDP", Value: 17},
 }
 
-const revision_64_fork = "96f1f19d85a4d091cba7b036633c3b48ccfe4439"
+const revision_64_fork = "1c9fe1f1a1f6f871fc5c088ca80174655322aca4"
diff --git a/sys/test/gen/empty.go b/sys/test/gen/empty.go
new file mode 100644
index 000000000..5baff07bf
--- /dev/null
+++ b/sys/test/gen/empty.go
@@ -0,0 +1,3 @@
+// AUTOGENERATED FILE
+// This file is needed if OS is completely excluded by build tags.
+package gen
diff --git a/sys/test/init.go b/sys/test/init.go
index 8e67fd754..815c99a98 100644
--- a/sys/test/init.go
+++ b/sys/test/init.go
@@ -6,16 +6,8 @@ package test
 import (
 	"github.com/google/syzkaller/prog"
 	"github.com/google/syzkaller/sys/targets"
-	"github.com/google/syzkaller/sys/test/gen"
 )
 
-func init() {
-	prog.RegisterTarget(gen.Target_64, initTarget)
-	prog.RegisterTarget(gen.Target_64_fork, initTarget)
-	prog.RegisterTarget(gen.Target_32_shmem, initTarget)
-	prog.RegisterTarget(gen.Target_32_fork_shmem, initTarget)
-}
-
-func initTarget(target *prog.Target) {
+func InitTarget(target *prog.Target) {
 	target.MakeMmap = targets.MakeSyzMmap(target)
 }
diff --git a/sys/windows/gen/amd64.go b/sys/windows/gen/amd64.go
index 47cf0eae3..445fc3d01 100644
--- a/sys/windows/gen/amd64.go
+++ b/sys/windows/gen/amd64.go
@@ -1,10 +1,14 @@
 // AUTOGENERATED FILE
+// +build !syz_target syz_target,syz_os_windows,syz_arch_amd64
 
 package gen
 
 import . "github.com/google/syzkaller/prog"
+import . "github.com/google/syzkaller/sys/windows"
 
-var Target_amd64 = &Target{OS: "windows", Arch: "amd64", Revision: revision_amd64, PtrSize: 8, PageSize: 4096, NumPages: 4096, DataOffset: 536870912, Syscalls: syscalls_amd64, Resources: resources_amd64, Structs: structDescs_amd64, Consts: consts_amd64}
+func init() {
+	RegisterTarget(&Target{OS: "windows", Arch: "amd64", Revision: revision_amd64, PtrSize: 8, PageSize: 4096, NumPages: 4096, DataOffset: 536870912, Syscalls: syscalls_amd64, Resources: resources_amd64, Structs: structDescs_amd64, Consts: consts_amd64}, InitTarget)
+}
 
 var resources_amd64 = []*ResourceDesc{
 	{Name: "HANDLE", Type: &IntType{IntTypeCommon: IntTypeCommon{TypeCommon: TypeCommon{TypeName: "intptr", TypeSize: 8}}}, Kind: []string{"HANDLE"}, Values: []uint64{18446744073709551615}},
@@ -14611,4 +14615,4 @@ var consts_amd64 = []ConstValue{
 	{Name: "WRITE_OWNER", Value: 524288},
 }
 
-const revision_amd64 = "e9562f6b9973e9e9a9522fd8ec12b4e913f13b4c"
+const revision_amd64 = "f2b48fb82a68b0cb24b2ab9638add66deb9542dd"
diff --git a/sys/windows/gen/empty.go b/sys/windows/gen/empty.go
new file mode 100644
index 000000000..5baff07bf
--- /dev/null
+++ b/sys/windows/gen/empty.go
@@ -0,0 +1,3 @@
+// AUTOGENERATED FILE
+// This file is needed if OS is completely excluded by build tags.
+package gen
diff --git a/sys/windows/init.go b/sys/windows/init.go
index f27f89cb0..2c165cea7 100644
--- a/sys/windows/init.go
+++ b/sys/windows/init.go
@@ -5,14 +5,9 @@ package windows
 
 import (
 	"github.com/google/syzkaller/prog"
-	"github.com/google/syzkaller/sys/windows/gen"
 )
 
-func init() {
-	prog.RegisterTarget(gen.Target_amd64, initTarget)
-}
-
-func initTarget(target *prog.Target) {
+func InitTarget(target *prog.Target) {
 	arch := &arch{
 		virtualAllocSyscall:    target.SyscallMap["VirtualAlloc"],
 		MEM_COMMIT:             target.ConstMap["MEM_COMMIT"],