cgo: add support for CFLAGS in .c files

This patch adds support for passing CFLAGS added in #cgo lines of the
CGo preprocessing phase to the compiler when compiling C files inside
packages. This is expected and convenient but didn't work before.

builder/build.go

@@ -430,7 +430,7 @@ func Build(pkgName, outpath string, config *compileopts.Config, action func(Buil
 		job := &compileJob{
 			description: "compile extra file " + path,
 			run: func(job *compileJob) error {
-				result, err := compileAndCacheCFile(abspath, dir, config)
+				result, err := compileAndCacheCFile(abspath, dir, config.CFlags(), config)
 				job.result = result
 				return err
 			},
@@ -443,12 +443,13 @@ func Build(pkgName, outpath string, config *compileopts.Config, action func(Buil
 	// TODO: do this as part of building the package to be able to link the
 	// bitcode files together.
 	for _, pkg := range lprogram.Sorted() {
+		pkg := pkg
 		for _, filename := range pkg.CFiles {
 			abspath := filepath.Join(pkg.Dir, filename)
 			job := &compileJob{
 				description: "compile CGo file " + abspath,
 				run: func(job *compileJob) error {
-					result, err := compileAndCacheCFile(abspath, dir, config)
+					result, err := compileAndCacheCFile(abspath, dir, pkg.CFlags, config)
 					job.result = result
 					return err
 				},

builder/cc.go

@@ -57,7 +57,7 @@ import (
 //   depfile but without invalidating its name. For this reason, the depfile is
 //   written on each new compilation (even when it seems unnecessary). However, it
 //   could in rare cases lead to a stale file fetched from the cache.
-func compileAndCacheCFile(abspath, tmpdir string, config *compileopts.Config) (string, error) {
+func compileAndCacheCFile(abspath, tmpdir string, cflags []string, config *compileopts.Config) (string, error) {
 	// Hash input file.
 	fileHash, err := hashFile(abspath)
 	if err != nil {
@@ -121,7 +121,7 @@ func compileAndCacheCFile(abspath, tmpdir string, config *compileopts.Config) (s
 		return "", err
 	}
 	depTmpFile.Close()
-	flags := config.CFlags()
+	flags := append([]string{}, cflags...)                                   // copy cflags
 	flags = append(flags, "-MD", "-MV", "-MTdeps", "-MF", depTmpFile.Name()) // autogenerate dependencies
 	flags = append(flags, "-c", "-o", objTmpFile.Name(), abspath)
 	if config.Options.PrintCommands {

cgo/cgo.go

@@ -41,7 +41,8 @@ type cgoPackage struct {
 	elaboratedTypes map[string]*elaboratedTypeInfo
 	enums           map[string]enumInfo
 	anonStructNum   int
-	ldflags         []string
+	cflags          []string // CFlags from #cgo lines
+	ldflags         []string // LDFlags from #cgo lines
 	visitedFiles    map[string][]byte
 }
 
@@ -157,10 +158,10 @@ typedef unsigned long long  _Cgo_ulonglong;
 // Process extracts `import "C"` statements from the AST, parses the comment
 // with libclang, and modifies the AST to use this information. It returns a
 // newly created *ast.File that should be added to the list of to-be-parsed
-// files, the LDFLAGS for this package, and a map of file hashes of the accessed
-// C header files. If there is one or more error, it returns these in the
-// []error slice but still modifies the AST.
-func Process(files []*ast.File, dir string, fset *token.FileSet, cflags []string) (*ast.File, []string, map[string][]byte, []error) {
+// files, the CFLAGS and LDFLAGS found in #cgo lines, and a map of file hashes
+// of the accessed C header files. If there is one or more error, it returns
+// these in the []error slice but still modifies the AST.
+func Process(files []*ast.File, dir string, fset *token.FileSet, cflags []string) (*ast.File, []string, []string, map[string][]byte, []error) {
 	p := &cgoPackage{
 		dir:             dir,
 		fset:            fset,
@@ -175,11 +176,6 @@ func Process(files []*ast.File, dir string, fset *token.FileSet, cflags []string
 		visitedFiles:    map[string][]byte{},
 	}
 
-	// Disable _FORTIFY_SOURCE as it causes problems on macOS.
-	// Note that it is only disabled for memcpy (etc) calls made from Go, which
-	// have better alternatives anyway.
-	cflags = append(cflags, "-D_FORTIFY_SOURCE=0")
-
 	// Add a new location for the following file.
 	generatedTokenPos := p.fset.AddFile(dir+"/!cgo.go", -1, 0)
 	generatedTokenPos.SetLines([]int{0})
@@ -188,7 +184,7 @@ func Process(files []*ast.File, dir string, fset *token.FileSet, cflags []string
 	// Find the absolute path for this package.
 	packagePath, err := filepath.Abs(fset.File(files[0].Pos()).Name())
 	if err != nil {
-		return nil, nil, nil, []error{
+		return nil, nil, nil, nil, []error{
 			scanner.Error{
 				Pos: fset.Position(files[0].Pos()),
 				Msg: "cgo: cannot find absolute path: " + err.Error(), // TODO: wrap this error
@@ -363,7 +359,7 @@ func Process(files []*ast.File, dir string, fset *token.FileSet, cflags []string
 						continue
 					}
 					makePathsAbsolute(flags, packagePath)
-					cflags = append(cflags, flags...)
+					p.cflags = append(p.cflags, flags...)
 				case "LDFLAGS":
 					flags, err := shlex.Split(value)
 					if err != nil {
@@ -386,6 +382,13 @@ func Process(files []*ast.File, dir string, fset *token.FileSet, cflags []string
 		}
 	}
 
+	// Define CFlags that will be used while parsing the package.
+	// Disable _FORTIFY_SOURCE as it causes problems on macOS.
+	// Note that it is only disabled for memcpy (etc) calls made from Go, which
+	// have better alternatives anyway.
+	cflagsForCGo := append([]string{"-D_FORTIFY_SOURCE=0"}, cflags...)
+	cflagsForCGo = append(cflagsForCGo, p.cflags...)
+
 	// Process all CGo imports.
 	for _, genDecl := range statements {
 		cgoComment := genDecl.Doc.Text()
@@ -395,7 +398,7 @@ func Process(files []*ast.File, dir string, fset *token.FileSet, cflags []string
 			pos = genDecl.Doc.Pos()
 		}
 		position := fset.PositionFor(pos, true)
-		p.parseFragment(cgoComment+cgoTypes, cflags, position.Filename, position.Line)
+		p.parseFragment(cgoComment+cgoTypes, cflagsForCGo, position.Filename, position.Line)
 	}
 
 	// Declare functions found by libclang.
@@ -430,7 +433,7 @@ func Process(files []*ast.File, dir string, fset *token.FileSet, cflags []string
 	// Print the newly generated in-memory AST, for debugging.
 	//ast.Print(fset, p.generated)
 
-	return p.generated, p.ldflags, p.visitedFiles, p.errors
+	return p.generated, p.cflags, p.ldflags, p.visitedFiles, p.errors
 }
 
 // makePathsAbsolute converts some common path compiler flags (-I, -L) from

cgo/cgo_test.go

@@ -65,7 +65,7 @@ func TestCGo(t *testing.T) {
 			}
 
 			// Process the AST with CGo.
-			cgoAST, _, _, cgoErrors := Process([]*ast.File{f}, "testdata", fset, cflags)
+			cgoAST, _, _, _, cgoErrors := Process([]*ast.File{f}, "testdata", fset, cflags)
 
 			// Check the AST for type errors.
 			var typecheckErrors []error

loader/loader.go

@@ -382,14 +382,14 @@ func (p *Package) parseFiles() ([]*ast.File, error) {
 
 	// Do CGo processing.
 	if len(p.CgoFiles) != 0 {
-		var cflags []string
-		cflags = append(cflags, p.program.config.CFlags()...)
-		cflags = append(cflags, "-I"+p.Dir)
+		var initialCFlags []string
+		initialCFlags = append(initialCFlags, p.program.config.CFlags()...)
+		initialCFlags = append(initialCFlags, "-I"+p.Dir)
 		if p.program.clangHeaders != "" {
-			cflags = append(cflags, "-Xclang", "-internal-isystem", "-Xclang", p.program.clangHeaders)
+			initialCFlags = append(initialCFlags, "-Xclang", "-internal-isystem", "-Xclang", p.program.clangHeaders)
 		}
-		p.CFlags = cflags
-		generated, ldflags, accessedFiles, errs := cgo.Process(files, p.program.workingDir, p.program.fset, cflags)
+		generated, cflags, ldflags, accessedFiles, errs := cgo.Process(files, p.program.workingDir, p.program.fset, initialCFlags)
+		p.CFlags = append(initialCFlags, cflags...)
 		for path, hash := range accessedFiles {
 			p.FileHashes[path] = hash
 		}

testdata/cgo/main.c

@@ -20,6 +20,8 @@ int globalUnionSize = sizeof(globalUnion);
 option_t globalOption = optionG;
 bitfield_t globalBitfield = {244, 15, 1, 2, 47, 5};
 
+int cflagsConstant = SOME_CONSTANT;
+
 int smallEnumWidth = sizeof(option2_t);
 
 int fortytwo() {

testdata/cgo/main.go

@@ -5,6 +5,7 @@ int fortytwo(void);
 #include "main.h"
 int mul(int, int);
 #include <string.h>
+#cgo CFLAGS: -DSOME_CONSTANT=17
 */
 import "C"
 
@@ -118,6 +119,9 @@ func main() {
 	// Check that enums are considered the same width in C and CGo.
 	println("enum width matches:", unsafe.Sizeof(C.option2_t(0)) == uintptr(C.smallEnumWidth))
 
+	// Check whether CFLAGS are correctly passed on to compiled C files.
+	println("CFLAGS value:", C.cflagsConstant)
+
 	// libc: test whether C functions work at all.
 	buf1 := []byte("foobar\x00")
 	buf2 := make([]byte, len(buf1))

testdata/cgo/main.h

@@ -139,6 +139,8 @@ extern bitfield_t globalBitfield;
 
 extern int smallEnumWidth;
 
+extern int cflagsConstant;
+
 // test duplicate definitions
 int add(int a, int b);
 extern int global;

testdata/cgo/out.txt

@@ -58,4 +58,5 @@ option G: 12
 option 2A: 20
 option 3A: 21
 enum width matches: true
+CFLAGS value: 17
 copied string: foobar