std: Harmonize use of off_t between libc and Zig impls

Let's follow the libc/kernel convention and use an i64 for offsets, we
bitcast as needed and avoid the useless conditional casts.

Author: LemonBoy

lib/std/c.zig

@@ -89,13 +89,13 @@ pub extern "c" fn ftruncate(fd: c_int, length: off_t) c_int;
 pub extern "c" fn raise(sig: c_int) c_int;
 pub extern "c" fn read(fd: fd_t, buf: [*]u8, nbyte: usize) isize;
 pub extern "c" fn readv(fd: c_int, iov: [*]const iovec, iovcnt: c_uint) isize;
-pub extern "c" fn pread(fd: fd_t, buf: [*]u8, nbyte: usize, offset: u64) isize;
-pub extern "c" fn preadv(fd: c_int, iov: [*]const iovec, iovcnt: c_uint, offset: u64) isize;
+pub extern "c" fn pread(fd: fd_t, buf: [*]u8, nbyte: usize, offset: off_t) isize;
+pub extern "c" fn preadv(fd: c_int, iov: [*]const iovec, iovcnt: c_uint, offset: off_t) isize;
 pub extern "c" fn writev(fd: c_int, iov: [*]const iovec_const, iovcnt: c_uint) isize;
-pub extern "c" fn pwritev(fd: c_int, iov: [*]const iovec_const, iovcnt: c_uint, offset: u64) isize;
+pub extern "c" fn pwritev(fd: c_int, iov: [*]const iovec_const, iovcnt: c_uint, offset: off_t) isize;
 pub extern "c" fn write(fd: fd_t, buf: [*]const u8, nbyte: usize) isize;
-pub extern "c" fn pwrite(fd: fd_t, buf: [*]const u8, nbyte: usize, offset: u64) isize;
-pub extern "c" fn mmap(addr: ?*align(page_size) c_void, len: usize, prot: c_uint, flags: c_uint, fd: fd_t, offset: u64) *c_void;
+pub extern "c" fn pwrite(fd: fd_t, buf: [*]const u8, nbyte: usize, offset: off_t) isize;
+pub extern "c" fn mmap(addr: ?*align(page_size) c_void, len: usize, prot: c_uint, flags: c_uint, fd: fd_t, offset: off_t) *c_void;
 pub extern "c" fn munmap(addr: *align(page_size) c_void, len: usize) c_int;
 pub extern "c" fn mprotect(addr: *align(page_size) c_void, len: usize, prot: c_uint) c_int;
 pub extern "c" fn link(oldpath: [*:0]const u8, newpath: [*:0]const u8, flags: c_int) c_int;

lib/std/c/linux.zig

@@ -67,14 +67,14 @@ pub extern "c" fn fstat64(fd: fd_t, buf: *libc_stat) c_int;
 pub extern "c" fn fstatat64(dirfd: fd_t, path: [*:0]const u8, stat_buf: *libc_stat, flags: u32) c_int;
 pub extern "c" fn ftruncate64(fd: c_int, length: off_t) c_int;
 pub extern "c" fn getrlimit64(resource: rlimit_resource, rlim: *rlimit) c_int;
-pub extern "c" fn lseek64(fd: fd_t, offset: u64, whence: c_int) u64;
-pub extern "c" fn mmap64(addr: ?*align(std.mem.page_size) c_void, len: usize, prot: c_uint, flags: c_uint, fd: fd_t, offset: u64) *c_void;
+pub extern "c" fn lseek64(fd: fd_t, offset: i64, whence: c_int) i64;
+pub extern "c" fn mmap64(addr: ?*align(std.mem.page_size) c_void, len: usize, prot: c_uint, flags: c_uint, fd: fd_t, offset: i64) *c_void;
 pub extern "c" fn open64(path: [*:0]const u8, oflag: c_uint, ...) c_int;
 pub extern "c" fn openat64(fd: c_int, path: [*:0]const u8, oflag: c_uint, ...) c_int;
-pub extern "c" fn pread64(fd: fd_t, buf: [*]u8, nbyte: usize, offset: u64) isize;
-pub extern "c" fn preadv64(fd: c_int, iov: [*]const iovec, iovcnt: c_uint, offset: u64) isize;
-pub extern "c" fn pwrite64(fd: fd_t, buf: [*]const u8, nbyte: usize, offset: u64) isize;
-pub extern "c" fn pwritev64(fd: c_int, iov: [*]const iovec_const, iovcnt: c_uint, offset: u64) isize;
+pub extern "c" fn pread64(fd: fd_t, buf: [*]u8, nbyte: usize, offset: i64) isize;
+pub extern "c" fn preadv64(fd: c_int, iov: [*]const iovec, iovcnt: c_uint, offset: i64) isize;
+pub extern "c" fn pwrite64(fd: fd_t, buf: [*]const u8, nbyte: usize, offset: i64) isize;
+pub extern "c" fn pwritev64(fd: c_int, iov: [*]const iovec_const, iovcnt: c_uint, offset: i64) isize;
 pub extern "c" fn sendfile64(out_fd: fd_t, in_fd: fd_t, offset: ?*i64, count: usize) isize;
 pub extern "c" fn setrlimit64(resource: rlimit_resource, rlim: *const rlimit) c_int;
 

lib/std/os.zig

@@ -502,8 +502,9 @@ pub fn pread(fd: fd_t, buf: []u8, offset: u64) PReadError!usize {
     else
         system.pread;
 
+    const ioffset = @bitCast(i64, offset); // the OS treats this as unsigned
     while (true) {
-        const rc = pread_sym(fd, buf.ptr, adjusted_len, offset);
+        const rc = pread_sym(fd, buf.ptr, adjusted_len, ioffset);
         switch (errno(rc)) {
             0 => return @intCast(usize, rc),
             EINTR => continue,
@@ -577,12 +578,8 @@ pub fn ftruncate(fd: fd_t, length: u64) TruncateError!void {
         else
             system.ftruncate;
 
-        // XXX Pick a side and avoid this cast madness.
-        const casted_length = if (builtin.link_libc)
-            @bitCast(off_t, length)
-        else
-            length;
-        switch (errno(ftruncate_sym(fd, casted_length))) {
+        const ilen = @bitCast(i64, length); // the OS treats this as unsigned
+        switch (errno(ftruncate_sym(fd, ilen))) {
             0 => return,
             EINTR => continue,
             EFBIG => return error.FileTooBig,
@@ -912,8 +909,9 @@ pub fn pwrite(fd: fd_t, bytes: []const u8, offset: u64) PWriteError!usize {
     else
         system.pwrite;
 
+    const ioffset = @bitCast(i64, offset); // the OS treats this as unsigned
     while (true) {
-        const rc = pwrite_sym(fd, bytes.ptr, adjusted_len, offset);
+        const rc = pwrite_sym(fd, bytes.ptr, adjusted_len, ioffset);
         switch (errno(rc)) {
             0 => return @intCast(usize, rc),
             EINTR => continue,
@@ -3750,7 +3748,8 @@ pub fn mmap(
     else
         system.mmap;
 
-    const rc = mmap_sym(ptr, length, prot, flags, fd, offset);
+    const ioffset = @bitCast(i64, offset); // the OS treats this as unsigned
+    const rc = mmap_sym(ptr, length, prot, flags, fd, ioffset);
     const err = if (builtin.link_libc) blk: {
         if (rc != std.c.MAP_FAILED) return @ptrCast([*]align(mem.page_size) u8, @alignCast(mem.page_size, rc))[0..length];
         break :blk system._errno().*;
@@ -4104,8 +4103,14 @@ pub fn lseek_SET(fd: fd_t, offset: u64) SeekError!void {
             else => |err| return unexpectedErrno(err),
         }
     }
-    const ipos = @bitCast(i64, offset); // the OS treats this as unsigned
-    switch (errno(system.lseek(fd, ipos, SEEK_SET))) {
+
+    const lseek_sym = if (builtin.os.tag == .linux and builtin.link_libc)
+        system.lseek64
+    else
+        system.lseek;
+
+    const ioffset = @bitCast(i64, offset); // the OS treats this as unsigned
+    switch (errno(lseek_sym(fd, ioffset, SEEK_SET))) {
         0 => return,
         EBADF => unreachable, // always a race condition
         EINVAL => return error.Unseekable,
@@ -4146,7 +4151,13 @@ pub fn lseek_CUR(fd: fd_t, offset: i64) SeekError!void {
             else => |err| return unexpectedErrno(err),
         }
     }
-    switch (errno(system.lseek(fd, offset, SEEK_CUR))) {
+    const lseek_sym = if (builtin.os.tag == .linux and builtin.link_libc)
+        system.lseek64
+    else
+        system.lseek;
+
+    const ioffset = @bitCast(i64, offset); // the OS treats this as unsigned
+    switch (errno(lseek_sym(fd, ioffset, SEEK_CUR))) {
         0 => return,
         EBADF => unreachable, // always a race condition
         EINVAL => return error.Unseekable,
@@ -4192,7 +4203,8 @@ pub fn lseek_END(fd: fd_t, offset: i64) SeekError!void {
     else
         system.lseek;
 
-    switch (errno(lseek_sym(fd, offset, SEEK_END))) {
+    const ioffset = @bitCast(i64, offset); // the OS treats this as unsigned
+    switch (errno(lseek_sym(fd, ioffset, SEEK_END))) {
         0 => return,
         EBADF => unreachable, // always a race condition
         EINVAL => return error.Unseekable,

lib/std/os/linux.zig

@@ -59,15 +59,16 @@ const require_aligned_register_pair =
     std.Target.current.cpu.arch.isThumb();
 
 // Split a 64bit value into a {LSB,MSB} pair.
-fn splitValue64(val: u64) [2]u32 {
+fn splitValue64(val: i64) [2]u32 {
+    const u = @bitCast(u64, val);
     switch (builtin.endian) {
         .Little => return [2]u32{
-            @truncate(u32, val),
-            @truncate(u32, val >> 32),
+            @truncate(u32, u),
+            @truncate(u32, u >> 32),
         },
         .Big => return [2]u32{
-            @truncate(u32, val >> 32),
-            @truncate(u32, val),
+            @truncate(u32, u >> 32),
+            @truncate(u32, u),
         },
     }
 }
@@ -243,7 +244,7 @@ pub fn umount2(special: [*:0]const u8, flags: u32) usize {
     return syscall2(.umount2, @ptrToInt(special), flags);
 }
 
-pub fn mmap(address: ?[*]u8, length: usize, prot: usize, flags: u32, fd: i32, offset: u64) usize {
+pub fn mmap(address: ?[*]u8, length: usize, prot: usize, flags: u32, fd: i32, offset: i64) usize {
     if (@hasField(SYS, "mmap2")) {
         // Make sure the offset is also specified in multiples of page size
         if ((offset & (MMAP2_UNIT - 1)) != 0)
@@ -256,7 +257,7 @@ pub fn mmap(address: ?[*]u8, length: usize, prot: usize, flags: u32, fd: i32, of
             prot,
             flags,
             @bitCast(usize, @as(isize, fd)),
-            @truncate(usize, offset / MMAP2_UNIT),
+            @truncate(usize, @bitCast(u64, offset) / MMAP2_UNIT),
         );
     } else {
         return syscall6(
@@ -266,7 +267,7 @@ pub fn mmap(address: ?[*]u8, length: usize, prot: usize, flags: u32, fd: i32, of
             prot,
             flags,
             @bitCast(usize, @as(isize, fd)),
-            offset,
+            @bitCast(u64, offset),
         );
     }
 }
@@ -308,7 +309,7 @@ pub fn read(fd: i32, buf: [*]u8, count: usize) usize {
     return syscall3(.read, @bitCast(usize, @as(isize, fd)), @ptrToInt(buf), count);
 }
 
-pub fn preadv(fd: i32, iov: [*]const iovec, count: usize, offset: u64) usize {
+pub fn preadv(fd: i32, iov: [*]const iovec, count: usize, offset: i64) usize {
     const offset_halves = splitValue64(offset);
     return syscall5(
         .preadv,
@@ -320,7 +321,7 @@ pub fn preadv(fd: i32, iov: [*]const iovec, count: usize, offset: u64) usize {
     );
 }
 
-pub fn preadv2(fd: i32, iov: [*]const iovec, count: usize, offset: u64, flags: kernel_rwf) usize {
+pub fn preadv2(fd: i32, iov: [*]const iovec, count: usize, offset: i64, flags: kernel_rwf) usize {
     const offset_halves = splitValue64(offset);
     return syscall6(
         .preadv2,
@@ -341,7 +342,7 @@ pub fn writev(fd: i32, iov: [*]const iovec_const, count: usize) usize {
     return syscall3(.writev, @bitCast(usize, @as(isize, fd)), @ptrToInt(iov), count);
 }
 
-pub fn pwritev(fd: i32, iov: [*]const iovec_const, count: usize, offset: u64) usize {
+pub fn pwritev(fd: i32, iov: [*]const iovec_const, count: usize, offset: i64) usize {
     const offset_halves = splitValue64(offset);
     return syscall5(
         .pwritev,
@@ -353,7 +354,7 @@ pub fn pwritev(fd: i32, iov: [*]const iovec_const, count: usize, offset: u64) us
     );
 }
 
-pub fn pwritev2(fd: i32, iov: [*]const iovec_const, count: usize, offset: u64, flags: kernel_rwf) usize {
+pub fn pwritev2(fd: i32, iov: [*]const iovec_const, count: usize, offset: i64, flags: kernel_rwf) usize {
     const offset_halves = splitValue64(offset);
     return syscall6(
         .pwritev2,
@@ -386,7 +387,7 @@ pub fn symlinkat(existing: [*:0]const u8, newfd: i32, newpath: [*:0]const u8) us
     return syscall3(.symlinkat, @ptrToInt(existing), @bitCast(usize, @as(isize, newfd)), @ptrToInt(newpath));
 }
 
-pub fn pread(fd: i32, buf: [*]u8, count: usize, offset: u64) usize {
+pub fn pread(fd: i32, buf: [*]u8, count: usize, offset: i64) usize {
     if (@hasField(SYS, "pread64") and usize_bits < 64) {
         const offset_halves = splitValue64(offset);
         if (require_aligned_register_pair) {
@@ -417,7 +418,7 @@ pub fn pread(fd: i32, buf: [*]u8, count: usize, offset: u64) usize {
             @bitCast(usize, @as(isize, fd)),
             @ptrToInt(buf),
             count,
-            offset,
+            @bitCast(u64, offset),
         );
     }
 }
@@ -452,7 +453,7 @@ pub fn write(fd: i32, buf: [*]const u8, count: usize) usize {
     return syscall3(.write, @bitCast(usize, @as(isize, fd)), @ptrToInt(buf), count);
 }
 
-pub fn ftruncate(fd: i32, length: u64) usize {
+pub fn ftruncate(fd: i32, length: i64) usize {
     if (@hasField(SYS, "ftruncate64") and usize_bits < 64) {
         const length_halves = splitValue64(length);
         if (require_aligned_register_pair) {
@@ -475,12 +476,12 @@ pub fn ftruncate(fd: i32, length: u64) usize {
         return syscall2(
             .ftruncate,
             @bitCast(usize, @as(isize, fd)),
-            @truncate(usize, length),
+            @bitCast(usize, length),
         );
     }
 }
 
-pub fn pwrite(fd: i32, buf: [*]const u8, count: usize, offset: u64) usize {
+pub fn pwrite(fd: i32, buf: [*]const u8, count: usize, offset: i64) usize {
     if (@hasField(SYS, "pwrite64") and usize_bits < 64) {
         const offset_halves = splitValue64(offset);
 
@@ -512,7 +513,7 @@ pub fn pwrite(fd: i32, buf: [*]const u8, count: usize, offset: u64) usize {
             @bitCast(usize, @as(isize, fd)),
             @ptrToInt(buf),
             count,
-            offset,
+            @bitCast(u64, offset),
         );
     }
 }