syz-extract: select declaring printf or not

Kernels are standalone implementations and can have their own
implementations of functions that have different prototypes than
the standard ones. In the NetBSD case the kernel printf returns
void, and it is declared in <sys/systm.h> so avoid re-declaring it.
Select if we are going to declare printf or not depending on the OS.

sys/syz-extract/akaros.go

@@ -30,5 +30,5 @@ func (*akaros) processFile(arch *Arch, info *compiler.ConstInfo) (map[string]uin
 	for _, incdir := range info.Incdirs {
 		args = append(args, "-I"+filepath.Join(dir, incdir))
 	}
-	return extract(info, "gcc", args, "")
+	return extract(info, "gcc", args, "", true)
 }

sys/syz-extract/fetch.go

@@ -17,12 +17,13 @@ import (
 	"github.com/google/syzkaller/pkg/compiler"
 )
 
-func extract(info *compiler.ConstInfo, cc string, args []string, addSource string) (map[string]uint64, map[string]bool, error) {
+func extract(info *compiler.ConstInfo, cc string, args []string, addSource string, declarePrintf bool) (map[string]uint64, map[string]bool, error) {
 	data := &CompileData{
-		AddSource: addSource,
-		Defines:   info.Defines,
-		Includes:  info.Includes,
-		Values:    info.Consts,
+		AddSource:     addSource,
+		Defines:       info.Defines,
+		Includes:      info.Includes,
+		Values:        info.Consts,
+		DeclarePrintf: declarePrintf,
 	}
 	undeclared := make(map[string]bool)
 	bin, out, err := compile(cc, args, data)
@@ -88,10 +89,11 @@ func extract(info *compiler.ConstInfo, cc string, args []string, addSource strin
 }
 
 type CompileData struct {
-	AddSource string
-	Defines   map[string]string
-	Includes  []string
-	Values    []string
+	AddSource     string
+	Defines       map[string]string
+	Includes      []string
+	Values        []string
+	DeclarePrintf bool
 }
 
 func compile(cc string, args []string, data *CompileData) (bin string, out []byte, err error) {
@@ -144,7 +146,9 @@ var srcTemplate = template.Must(template.New("").Parse(`
 
 {{.AddSource}}
 
+{{.DeclarePrintf}}
 int printf(const char *format, ...);
+{{end}}
 
 int main() {
 	int i;

sys/syz-extract/freebsd.go

@@ -67,7 +67,7 @@ func (*freebsd) processFile(arch *Arch, info *compiler.ConstInfo) (map[string]ui
 			info.Consts = append(info.Consts, compat)
 		}
 	}
-	res, undeclared, err := extract(info, "gcc", args, "#include <sys/syscall.h>")
+	res, undeclared, err := extract(info, "gcc", args, "#include <sys/syscall.h>", true)
 	for orig, compats := range compatNames {
 		for _, compat := range compats {
 			if undeclared[orig] && !undeclared[compat] {

sys/syz-extract/fuchsia.go

@@ -31,5 +31,5 @@ func (*fuchsia) processFile(arch *Arch, info *compiler.ConstInfo) (map[string]ui
 	for _, incdir := range info.Incdirs {
 		args = append(args, "-I"+filepath.Join(dir, incdir))
 	}
-	return extract(info, cc, args, "")
+	return extract(info, cc, args, "", true)
 }

sys/syz-extract/linux.go

@@ -103,5 +103,5 @@ unsigned long phys_base;
 unsigned long __phys_addr(unsigned long addr) { return 0; }
 #endif
 `
-	return extract(info, "gcc", args, addSource)
+	return extract(info, "gcc", args, addSource, true)
 }

sys/syz-extract/netbsd.go

@@ -85,7 +85,7 @@ func (*netbsd) processFile(arch *Arch, info *compiler.ConstInfo) (map[string]uin
 			info.Consts = append(info.Consts, compat)
 		}
 	}
-	res, undeclared, err := extract(info, "gcc", args, "#include <sys/syscall.h>")
+	res, undeclared, err := extract(info, "gcc", args, "#include <sys/syscall.h>", false)
 	for orig, compats := range compatNames {
 		for _, compat := range compats {
 			if undeclared[orig] && !undeclared[compat] {

sys/syz-extract/windows.go

@@ -18,5 +18,5 @@ func (*windows) prepareArch(arch *Arch) error {
 }
 
 func (*windows) processFile(arch *Arch, info *compiler.ConstInfo) (map[string]uint64, map[string]bool, error) {
-	return extract(info, "cl", nil, "")
+	return extract(info, "cl", nil, "", true)
 }