Use weak! for setns, preadv64v2, and pwritev64v2 on GLIBC. (#556)

`setns`, `preadv64v2`, and `pwritev64v2` were introduced more recently than the earliest glibc we support, so use the `weak!` mechanism for them, with fallbacks using `syscall`.

Author: sunfishcode

src/backend/libc/offset.rs

@@ -213,8 +213,21 @@ pub(super) use c::posix_fadvise64 as libc_posix_fadvise;
 pub(super) use c::{pread as libc_pread, pwrite as libc_pwrite};
 #[cfg(any(target_os = "android", target_os = "linux", target_os = "emscripten"))]
 pub(super) use c::{pread64 as libc_pread, pwrite64 as libc_pwrite};
+#[cfg(not(any(
+ windows,
+ target_os = "android",
+ target_os = "emscripten",
+ target_os = "haiku",
+ target_os = "ios",
+ target_os = "linux",
+ target_os = "macos",
+ target_os = "redox",
+ target_os = "solaris",
+)))]
+pub(super) use c::{preadv as libc_preadv, pwritev as libc_pwritev};
 #[cfg(any(target_os = "linux", target_os = "emscripten"))]
 pub(super) use c::{preadv64 as libc_preadv, pwritev64 as libc_pwritev};
+
 #[cfg(target_os = "android")]
 mod readwrite_pv64 {
  use super::c;
@@ -302,20 +315,9 @@ mod readwrite_pv64 {
  }
  }
 }
-#[cfg(not(any(
- windows,
- target_os = "android",
- target_os = "emscripten",
- target_os = "haiku",
- target_os = "ios",
- target_os = "linux",
- target_os = "macos",
- target_os = "redox",
- target_os = "solaris",
-)))]
-pub(super) use c::{preadv as libc_preadv, pwritev as libc_pwritev};
 #[cfg(target_os = "android")]
 pub(super) use readwrite_pv64::{preadv64 as libc_preadv, pwritev64 as libc_pwritev};
+
 // macOS added preadv and pwritev in version 11.0
 #[cfg(any(target_os = "ios", target_os = "macos"))]
 mod readwrite_pv {
@@ -337,11 +339,104 @@ mod readwrite_pv {
  ) -> c::ssize_t
  }
 }
-#[cfg(all(target_os = "linux", target_env = "gnu"))]
-pub(super) use c::{preadv64v2 as libc_preadv2, pwritev64v2 as libc_pwritev2};
 #[cfg(any(target_os = "ios", target_os = "macos"))]
 pub(super) use readwrite_pv::{preadv as libc_preadv, pwritev as libc_pwritev};
 
+// GLIBC added `preadv64v2` and `pwritev64v2` in version 2.26.
+#[cfg(all(target_os = "linux", target_env = "gnu"))]
+mod readwrite_pv64v2 {
+ use super::c;
+
+ // 64-bit offsets on 32-bit platforms are passed in endianness-specific
+ // lo/hi pairs. See src/backend/linux_raw/conv.rs for details.
+ #[cfg(all(target_endian = "little", target_pointer_width = "32"))]
+ fn lo(x: u64) -> usize {
+ (x >> 32) as usize
+ }
+ #[cfg(all(target_endian = "little", target_pointer_width = "32"))]
+ fn hi(x: u64) -> usize {
+ (x & 0xffff_ffff) as usize
+ }
+ #[cfg(all(target_endian = "big", target_pointer_width = "32"))]
+ fn lo(x: u64) -> usize {
+ (x & 0xffff_ffff) as usize
+ }
+ #[cfg(all(target_endian = "big", target_pointer_width = "32"))]
+ fn hi(x: u64) -> usize {
+ (x >> 32) as usize
+ }
+
+ pub(in super::super) unsafe fn preadv64v2(
+ fd: c::c_int,
+ iov: *const c::iovec,
+ iovcnt: c::c_int,
+ offset: c::off64_t,
+ flags: c::c_int,
+ ) -> c::ssize_t {
+ // Older GLIBC lacks `preadv64v2`, so use the `weak!` mechanism to
+ // test for it, and call back to `c::syscall`. We don't use
+ // `weak_or_syscall` here because we need to pass the 64-bit offset
+ // specially.
+ weak! {
+ fn preadv64v2(c::c_int, *const c::iovec, c::c_int, c::off64_t, c::c_int) -> c::ssize_t
+ }
+ if let Some(fun) = preadv64v2.get() {
+ fun(fd, iov, iovcnt, offset, flags)
+ } else {
+ #[cfg(target_pointer_width = "32")]
+ {
+ c::syscall(
+ c::SYS_preadv,
+ fd,
+ iov,
+ iovcnt,
+ hi(offset as u64),
+ lo(offset as u64),
+ flags,
+ ) as c::ssize_t
+ }
+ #[cfg(target_pointer_width = "64")]
+ {
+ c::syscall(c::SYS_preadv2, fd, iov, iovcnt, offset, flags) as c::ssize_t
+ }
+ }
+ }
+ pub(in super::super) unsafe fn pwritev64v2(
+ fd: c::c_int,
+ iov: *const c::iovec,
+ iovcnt: c::c_int,
+ offset: c::off64_t,
+ flags: c::c_int,
+ ) -> c::ssize_t {
+ // See the comments in `preadv64v2`.
+ weak! {
+ fn pwritev64v2(c::c_int, *const c::iovec, c::c_int, c::off64_t, c::c_int) -> c::ssize_t
+ }
+ if let Some(fun) = pwritev64v2.get() {
+ fun(fd, iov, iovcnt, offset, flags)
+ } else {
+ #[cfg(target_pointer_width = "32")]
+ {
+ c::syscall(
+ c::SYS_pwritev,
+ fd,
+ iov,
+ iovcnt,
+ hi(offset as u64),
+ lo(offset as u64),
+ flags,
+ ) as c::ssize_t
+ }
+ #[cfg(target_pointer_width = "64")]
+ {
+ c::syscall(c::SYS_pwritev2, fd, iov, iovcnt, offset, flags) as c::ssize_t
+ }
+ }
+ }
+}
+#[cfg(all(target_os = "linux", target_env = "gnu"))]
+pub(super) use readwrite_pv64v2::{preadv64v2 as libc_preadv2, pwritev64v2 as libc_pwritev2};
+
 #[cfg(not(any(
  windows,
  target_os = "aix",

src/backend/libc/thread/syscalls.rs

@@ -291,7 +291,13 @@ pub(crate) fn gettid() -> Pid {
 #[cfg(any(target_os = "android", target_os = "linux"))]
 #[inline]
 pub(crate) fn setns(fd: BorrowedFd, nstype: c::c_int) -> io::Result<c::c_int> {
- unsafe { ret_c_int(c::setns(borrowed_fd(fd), nstype)) }
+ // `setns` wasn't supported in glibc until 2.14, and musl until 0.9.5,
+ // so use `syscall`.
+ weak_or_syscall! {
+ fn setns(fd: c::c_int, nstype: c::c_int) via SYS_setns -> c::c_int
+ }
+
+ unsafe { ret_c_int(setns(borrowed_fd(fd), nstype)) }
 }
 
 #[cfg(any(target_os = "android", target_os = "linux"))]