cmd/go, cmd/cgo: pass -mfp32 and -mhard/soft-float to MIPS GCC

For mips32 currently, we are using FP32, while the gcc may be FPXX,
which may generate .MIPS.abiflags and .gnu.attributes section with
value as FPXX. So the kernel will treat the exe as FPXX, and may
choose to use FR=1 FPU mode for it.
Currently, in Go, we use 2 lwc1 to load both half of a double value
to a pair of even-odd FPR. This behavior can only work with FR=0 mode.

In FR=1 mode, all of 32 FPR are 64bit. If we lwc1 the high-half of a double
value to an odd FPR, and try to use the previous even FPR to compute, the
real high-half of even FPR will be unpredicatable.
We set -mfp32 to force the gcc generate FP32 code and section value.

More details about FP32/FPXX/FP64 are explained in:
https://web.archive.org/web/20180828210612/https://dmz-portal.mips.com/wiki/MIPS_O32_ABI_-_FR0_and_FR1_Interlinking

When GOMIPS/GOMIPS64 is set as softfloat, we should also pass
 -msoft-float to gcc.

Here we also add -mno-odd-spreg option, since Loongson's CPU cannot use
odd-number FR in FR=0 mode.

Fixes #39435

Change-Id: I54026ad416a815fe43a9261ebf6d02e5519c3930
Reviewed-on: https://go-review.googlesource.com/c/go/+/237058
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Meng Zhuo <mzh@golangcn.org>

src/cmd/cgo/gcc.go

@@ -1566,9 +1566,17 @@ func (p *Package) gccMachine() []string {
 	case "s390x":
 		return []string{"-m64"}
 	case "mips64", "mips64le":
-		return []string{"-mabi=64"}
+		if gomips64 == "hardfloat" {
+			return []string{"-mabi=64", "-mhard-float"}
+		} else if gomips64 == "softfloat" {
+			return []string{"-mabi=64", "-msoft-float"}
+		}
 	case "mips", "mipsle":
-		return []string{"-mabi=32"}
+		if gomips == "hardfloat" {
+			return []string{"-mabi=32", "-mfp32", "-mhard-float", "-mno-odd-spreg"}
+		} else if gomips == "softfloat" {
+			return []string{"-mabi=32", "-msoft-float"}
+		}
 	}
 	return nil
 }

src/cmd/cgo/main.go

@@ -245,7 +245,7 @@ var importRuntimeCgo = flag.Bool("import_runtime_cgo", true, "import runtime/cgo
 var importSyscall = flag.Bool("import_syscall", true, "import syscall in generated code")
 var trimpath = flag.String("trimpath", "", "applies supplied rewrites or trims prefixes to recorded source file paths")
 
-var goarch, goos string
+var goarch, goos, gomips, gomips64 string
 
 func main() {
 	objabi.AddVersionFlag() // -V
@@ -405,6 +405,8 @@ func newPackage(args []string) *Package {
 	if s := os.Getenv("GOOS"); s != "" {
 		goos = s
 	}
+	gomips = objabi.GOMIPS
+	gomips64 = objabi.GOMIPS64
 	ptrSize := ptrSizeMap[goarch]
 	if ptrSize == 0 {
 		fatalf("unknown ptrSize for $GOARCH %q", goarch)

src/cmd/go/internal/work/exec.go

@@ -2599,9 +2599,19 @@ func (b *Builder) gccArchArgs() []string {
 	case "s390x":
 		return []string{"-m64", "-march=z196"}
 	case "mips64", "mips64le":
-		return []string{"-mabi=64"}
+		args := []string{"-mabi=64"}
+		if cfg.GOMIPS64 == "hardfloat" {
+			return append(args, "-mhard-float")
+		} else if cfg.GOMIPS64 == "softfloat" {
+			return append(args, "-msoft-float")
+		}
 	case "mips", "mipsle":
-		return []string{"-mabi=32", "-march=mips32"}
+		args := []string{"-mabi=32", "-march=mips32"}
+		if cfg.GOMIPS == "hardfloat" {
+			return append(args, "-mhard-float", "-mfp32", "-mno-odd-spreg")
+		} else if cfg.GOMIPS == "softfloat" {
+			return append(args, "-msoft-float")
+		}
 	case "ppc64":
 		if cfg.Goos == "aix" {
 			return []string{"-maix64"}