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.

builder/build.go

@@ -176,11 +176,12 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
 		defer unlock()
 		libcDependencies = append(libcDependencies, libcJob)
 	case "mingw-w64":
-		_, unlock, err := libMinGW.load(config, tmpdir)
+		job, unlock, err := libMinGW.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 libMinGW = 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 libMusl = 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 libMusl = 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 libPicolibc = 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",