cgo: add support for printf

The C printf function is sometimes needed for C files included using
CGo. This commit makes sure they're available on all systems where CGo
is fully supported (that is, everywhere except on AVR).

For baremetal systems using picolibc, I've picked the integer-only
version of printf to save on flash size. We might want to consider
providing a way to pick the floating point version instead, if needed.

GNUmakefile

@@ -806,6 +806,7 @@ build/release: tinygo gen-device wasi-libc $(if $(filter 1,$(USE_SYSTEM_BINARYEN
 	@mkdir -p build/release/tinygo/lib/CMSIS/CMSIS
 	@mkdir -p build/release/tinygo/lib/macos-minimal-sdk
 	@mkdir -p build/release/tinygo/lib/mingw-w64/mingw-w64-crt/lib-common
+	@mkdir -p build/release/tinygo/lib/mingw-w64/mingw-w64-crt/stdio
 	@mkdir -p build/release/tinygo/lib/mingw-w64/mingw-w64-headers/defaults
 	@mkdir -p build/release/tinygo/lib/musl/arch
 	@mkdir -p build/release/tinygo/lib/musl/crt
@@ -840,10 +841,12 @@ endif
 	@cp -rp lib/musl/src/include         build/release/tinygo/lib/musl/src
 	@cp -rp lib/musl/src/internal        build/release/tinygo/lib/musl/src
 	@cp -rp lib/musl/src/legacy          build/release/tinygo/lib/musl/src
+	@cp -rp lib/musl/src/locale          build/release/tinygo/lib/musl/src
 	@cp -rp lib/musl/src/linux           build/release/tinygo/lib/musl/src
 	@cp -rp lib/musl/src/malloc          build/release/tinygo/lib/musl/src
 	@cp -rp lib/musl/src/mman            build/release/tinygo/lib/musl/src
 	@cp -rp lib/musl/src/math            build/release/tinygo/lib/musl/src
+	@cp -rp lib/musl/src/multibyte       build/release/tinygo/lib/musl/src
 	@cp -rp lib/musl/src/signal          build/release/tinygo/lib/musl/src
 	@cp -rp lib/musl/src/stdio           build/release/tinygo/lib/musl/src
 	@cp -rp lib/musl/src/string          build/release/tinygo/lib/musl/src
@@ -853,6 +856,7 @@ endif
 	@cp -rp lib/mingw-w64/mingw-w64-crt/def-include                 build/release/tinygo/lib/mingw-w64/mingw-w64-crt
 	@cp -rp lib/mingw-w64/mingw-w64-crt/lib-common/api-ms-win-crt-* build/release/tinygo/lib/mingw-w64/mingw-w64-crt/lib-common
 	@cp -rp lib/mingw-w64/mingw-w64-crt/lib-common/kernel32.def.in  build/release/tinygo/lib/mingw-w64/mingw-w64-crt/lib-common
+	@cp -rp lib/mingw-w64/mingw-w64-crt/stdio/ucrt_*                build/release/tinygo/lib/mingw-w64/mingw-w64-crt/stdio
 	@cp -rp lib/mingw-w64/mingw-w64-headers/crt/                    build/release/tinygo/lib/mingw-w64/mingw-w64-headers
 	@cp -rp lib/mingw-w64/mingw-w64-headers/defaults/include        build/release/tinygo/lib/mingw-w64/mingw-w64-headers/defaults
 	@cp -rp lib/nrfx/*                   build/release/tinygo/lib/nrfx

builder/build.go

@@ -169,11 +169,12 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
 		}
 		libcDependencies = append(libcDependencies, dummyCompileJob(path))
 	case "mingw-w64":
-		_, unlock, err := MinGW.load(config, tmpdir)
+		job, unlock, err := MinGW.load(config, tmpdir)
 		if err != nil {
 			return BuildResult{}, err
 		}
-		unlock()
+		defer unlock()
+		libcDependencies = append(libcDependencies, job)
 		libcDependencies = append(libcDependencies, makeMinGWExtraLibs(tmpdir, config.GOARCH())...)
 	case "":
 		// no library specified, so nothing to do

builder/mingw-w64.go

@@ -27,14 +27,30 @@ var MinGW = Library{
 		_, err = io.Copy(outf, inf)
 		return err
 	},
-	sourceDir: func() string { return "" }, // unused
+	sourceDir: func() string { return filepath.Join(goenv.Get("TINYGOROOT"), "lib/mingw-w64") },
 	cflags: func(target, headerPath string) []string {
-		// No flags necessary because there are no files to compile.
-		return nil
+		mingwDir := filepath.Join(goenv.Get("TINYGOROOT"), "lib/mingw-w64")
+		return []string{
+			"-nostdlibinc",
+			"-isystem", mingwDir + "/mingw-w64-headers/crt",
+			"-I", mingwDir + "/mingw-w64-headers/defaults/include",
+			"-I" + headerPath,
+		}
 	},
 	librarySources: func(target string) ([]string, error) {
-		// We only use the UCRT DLL file. No source files necessary.
-		return nil, nil
+		// These files are needed so that printf and the like are supported.
+		sources := []string{
+			"mingw-w64-crt/stdio/ucrt_fprintf.c",
+			"mingw-w64-crt/stdio/ucrt_fwprintf.c",
+			"mingw-w64-crt/stdio/ucrt_printf.c",
+			"mingw-w64-crt/stdio/ucrt_snprintf.c",
+			"mingw-w64-crt/stdio/ucrt_sprintf.c",
+			"mingw-w64-crt/stdio/ucrt_vfprintf.c",
+			"mingw-w64-crt/stdio/ucrt_vprintf.c",
+			"mingw-w64-crt/stdio/ucrt_vsnprintf.c",
+			"mingw-w64-crt/stdio/ucrt_vsprintf.c",
+		}
+		return sources, nil
 	},
 }
 

builder/musl.go

@@ -92,6 +92,8 @@ var Musl = Library{
 			"-Wno-ignored-pragmas",
 			"-Wno-tautological-constant-out-of-range-compare",
 			"-Wno-deprecated-non-prototype",
+			"-Wno-format",
+			"-Wno-parentheses",
 			"-Qunused-arguments",
 			// Select include dirs. Don't include standard library includes
 			// (that would introduce host dependencies and other complications),
@@ -119,11 +121,13 @@ var Musl = Library{
 			"internal/syscall_ret.c",
 			"internal/vdso.c",
 			"legacy/*.c",
+			"locale/*.c",
 			"linux/*.c",
 			"malloc/*.c",
 			"malloc/mallocng/*.c",
 			"mman/*.c",
 			"math/*.c",
+			"multibyte/*.c",
 			"signal/*.c",
 			"stdio/*.c",
 			"string/*.c",

builder/picolibc.go

@@ -29,6 +29,7 @@ var Picolibc = Library{
 			"-D_HAVE_ALIAS_ATTRIBUTE",
 			"-DTINY_STDIO",
 			"-DPOSIX_IO",
+			"-DFORMAT_DEFAULT_INTEGER", // use __i_vfprintf and __i_vfscanf by default
 			"-D_IEEE_LIBM",
 			"-D__OBSOLETE_MATH_FLOAT=1", // use old math code that doesn't expect a FPU
 			"-D__OBSOLETE_MATH_DOUBLE=0",

testdata/cgo/main.c

@@ -1,4 +1,5 @@
 #include "main.h"
+#include <stdio.h>
 
 int global = 3;
 bool globalBool = 1;
@@ -67,3 +68,7 @@ void unionSetData(short f0, short f1, short f2) {
 void arraydecay(int buf1[5], int buf2[3][8], int buf3[4][7][2]) {
 	// Do nothing.
 }
+
+void printf_single_int(char *format, int arg) {
+	printf(format, arg);
+}

testdata/cgo/main.go

@@ -174,6 +174,10 @@ func main() {
 	// libc: test basic stdio functionality
 	putsBuf := []byte("line written using C puts\x00")
 	C.puts((*C.char)(unsafe.Pointer(&putsBuf[0])))
+
+	// libc: test whether printf works in C.
+	printfBuf := []byte("line written using C printf with value=%d\n\x00")
+	C.printf_single_int((*C.char)(unsafe.Pointer(&printfBuf[0])), -21)
 }
 
 func printUnion(union C.joined_t) C.joined_t {

testdata/cgo/main.h

@@ -150,3 +150,5 @@ extern int global;
 // Test array decaying into a pointer.
 typedef int arraydecay_buf3[4][7][2];
 void arraydecay(int buf1[5], int buf2[3][8], arraydecay_buf3 buf3);
+
+void printf_single_int(char *format, int arg);

testdata/cgo/out.txt

@@ -75,3 +75,4 @@ len(C.GoStringN(nil, 0)): 0
 len(C.GoBytes(nil, 0)): 0
 copied string: foobar
 line written using C puts
+line written using C printf with value=-21