internal/runtime/syscall: add basic file system calls

Change-Id: I6a6a636c5e119165dc1018d1fc0354f5b6929656
Reviewed-on: https://go-review.googlesource.com/c/go/+/670496
Auto-Submit: Michael Pratt <mpratt@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

1 files changed, 45 insertions, 0 deletions

diff --git a/src/internal/runtime/syscall/syscall_linux.go b/src/internal/runtime/syscall/syscall_linux.go
index 83df825169..49e5f8de2c 100644
--- a/src/internal/runtime/syscall/syscall_linux.go
+++ b/src/internal/runtime/syscall/syscall_linux.go
@@ -6,6 +6,7 @@
 package syscall
 
 import (
+	"internal/goarch"
 	"unsafe"
 )
 
@@ -42,3 +43,47 @@ func Eventfd(initval, flags int32) (fd int32, errno uintptr) {
 	r1, _, e := Syscall6(SYS_EVENTFD2, uintptr(initval), uintptr(flags), 0, 0, 0, 0)
 	return int32(r1), e
 }
+
+func Open(path *byte, mode int, perm uint32) (fd int, errno uintptr) {
+	// Use SYS_OPENAT to match the syscall package.
+	dfd := AT_FDCWD
+	r1, _, e := Syscall6(SYS_OPENAT, uintptr(dfd), uintptr(unsafe.Pointer(path)), uintptr(mode|O_LARGEFILE), uintptr(perm), 0, 0)
+	return int(r1), e
+}
+
+func Close(fd int) (errno uintptr) {
+	_, _, e := Syscall6(SYS_CLOSE, uintptr(fd), 0, 0, 0, 0, 0)
+	return e
+}
+
+func Read(fd int, p []byte) (n int, errno uintptr) {
+	var p0 unsafe.Pointer
+	if len(p) > 0 {
+		p0 = unsafe.Pointer(&p[0])
+	} else {
+		p0 = unsafe.Pointer(&_zero)
+	}
+	r1, _, e := Syscall6(SYS_READ, uintptr(fd), uintptr(p0), uintptr(len(p)), 0, 0, 0)
+	return int(r1), e
+}
+
+func Pread(fd int, p []byte, offset int64) (n int, errno uintptr) {
+	var p0 unsafe.Pointer
+	if len(p) > 0 {
+		p0 = unsafe.Pointer(&p[0])
+	} else {
+		p0 = unsafe.Pointer(&_zero)
+	}
+	var r1, e uintptr
+	switch goarch.GOARCH {
+	case "386":
+		r1, _, e = Syscall6(SYS_PREAD64, uintptr(fd), uintptr(p0), uintptr(len(p)), uintptr(offset), uintptr(offset>>32), 0)
+	case "arm", "mipsle":
+		r1, _, e = Syscall6(SYS_PREAD64, uintptr(fd), uintptr(p0), uintptr(len(p)), 0, uintptr(offset), uintptr(offset>>32))
+	case "mips":
+		r1, _, e = Syscall6(SYS_PREAD64, uintptr(fd), uintptr(p0), uintptr(len(p)), 0, uintptr(offset>>32), uintptr(offset))
+	default:
+		r1, _, e = Syscall6(SYS_PREAD64, uintptr(fd), uintptr(p0), uintptr(len(p)), uintptr(offset), 0, 0)
+	}
+	return int(r1), e
+}