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Auto merge of #90846 - cuviper:weak, r=dtolnay

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Refactor weak symbols in std::sys::unix

This makes a few changes to the weak symbol macros in `sys::unix`:

- `dlsym!` is added to keep the functionality for runtime `dlsym`
  lookups, like for `__pthread_get_minstack@GLIBC_PRIVATE` that we don't
  want to show up in ELF symbol tables.
- `weak!` now uses `#[linkage = "extern_weak"]` symbols, so its runtime
  behavior is just a simple null check. This is also used by `syscall!`.
  - On non-ELF targets (macos/ios) where that linkage is not known to
    behave, `weak!` is just an alias to `dlsym!` for the old behavior.
- `raw_syscall!` is added to always call `libc::syscall` on linux and
  android, for cases like `clone3` that have no known libc wrapper.

The new `weak!` linkage does mean that you'll get versioned symbols if
you build with a newer glibc, like `WEAK DEFAULT UND statx@GLIBC_2.28`.
This might seem problematic, but old non-weak symbols can tie the build
to new versions too, like `dlsym@GLIBC_2.34` from their recent library
unification. If you build with an old glibc like `dist-x86_64-linux`
does, you'll still get unversioned `WEAK DEFAULT UND statx`, which may
be resolved based on the runtime glibc.

I also found a few functions that don't need to be weak anymore:

- Android can directly use `ftruncate64`, `pread64`, and `pwrite64`, as
  these were added in API 12, and our baseline is API 14.
- Linux can directly use `splice`, added way back in glibc 2.5 and
  similarly old musl. Android only added it in API 21 though.
This commit is contained in:
bors 2021-11-27 07:58:00 +00:00
commit 0881b3abe4
10 changed files with 136 additions and 193 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

90
library/std/src/sys/unix/android.rs
View File

@ -18,11 +18,9 @@
#![cfg(target_os = "android")]
use libc::{c_int, c_void, sighandler_t, size_t, ssize_t};
use libc::{ftruncate, pread, pwrite};
use libc::{c_int, sighandler_t};
use super::{cvt, cvt_r, weak::weak};
use crate::io;
use super::weak::weak;
// The `log2` and `log2f` functions apparently appeared in android-18, or at
// least you can see they're not present in the android-17 header [1] and they
@ -81,87 +79,3 @@ pub unsafe fn signal(signum: c_int, handler: sighandler_t) -> sighandler_t {
let f = f.expect("neither `signal` nor `bsd_signal` symbols found");
f(signum, handler)
}
// The `ftruncate64` symbol apparently appeared in android-12, so we do some
// dynamic detection to see if we can figure out whether `ftruncate64` exists.
//
// If it doesn't we just fall back to `ftruncate`, generating an error for
// too-large values.
#[cfg(target_pointer_width = "32")]
pub fn ftruncate64(fd: c_int, size: u64) -> io::Result<()> {
weak!(fn ftruncate64(c_int, i64) -> c_int);
unsafe {
match ftruncate64.get() {
Some(f) => cvt_r(|| f(fd, size as i64)).map(drop),
None => {
if size > i32::MAX as u64 {
Err(io::Error::new_const(io::ErrorKind::InvalidInput, &"cannot truncate >2GB"))
} else {
cvt_r(|| ftruncate(fd, size as i32)).map(drop)
}
}
}
}
}
#[cfg(target_pointer_width = "64")]
pub fn ftruncate64(fd: c_int, size: u64) -> io::Result<()> {
unsafe { cvt_r(|| ftruncate(fd, size as i64)).map(drop) }
}
#[cfg(target_pointer_width = "32")]
pub unsafe fn cvt_pread64(
fd: c_int,
buf: *mut c_void,
count: size_t,
offset: i64,
) -> io::Result<ssize_t> {
use crate::convert::TryInto;
weak!(fn pread64(c_int, *mut c_void, size_t, i64) -> ssize_t);
pread64.get().map(|f| cvt(f(fd, buf, count, offset))).unwrap_or_else(|| {
if let Ok(o) = offset.try_into() {
cvt(pread(fd, buf, count, o))
} else {
Err(io::Error::new_const(io::ErrorKind::InvalidInput, &"cannot pread >2GB"))
}
})
}
#[cfg(target_pointer_width = "32")]
pub unsafe fn cvt_pwrite64(
fd: c_int,
buf: *const c_void,
count: size_t,
offset: i64,
) -> io::Result<ssize_t> {
use crate::convert::TryInto;
weak!(fn pwrite64(c_int, *const c_void, size_t, i64) -> ssize_t);
pwrite64.get().map(|f| cvt(f(fd, buf, count, offset))).unwrap_or_else(|| {
if let Ok(o) = offset.try_into() {
cvt(pwrite(fd, buf, count, o))
} else {
Err(io::Error::new_const(io::ErrorKind::InvalidInput, &"cannot pwrite >2GB"))
}
})
}
#[cfg(target_pointer_width = "64")]
pub unsafe fn cvt_pread64(
fd: c_int,
buf: *mut c_void,
count: size_t,
offset: i64,
) -> io::Result<ssize_t> {
cvt(pread(fd, buf, count, offset))
}
#[cfg(target_pointer_width = "64")]
pub unsafe fn cvt_pwrite64(
fd: c_int,
buf: *const c_void,
count: size_t,
offset: i64,
) -> io::Result<ssize_t> {
cvt(pwrite(fd, buf, count, offset))
}

48
library/std/src/sys/unix/fd.rs
View File

@ -99,30 +99,18 @@ pub fn read_to_end(&self, buf: &mut Vec<u8>) -> io::Result<usize> {
}
pub fn read_at(&self, buf: &mut [u8], offset: u64) -> io::Result<usize> {
#[cfg(target_os = "android")]
use super::android::cvt_pread64;
#[cfg(not(target_os = "android"))]
unsafe fn cvt_pread64(
fd: c_int,
buf: *mut c_void,
count: usize,
offset: i64,
) -> io::Result<isize> {
#[cfg(not(target_os = "linux"))]
use libc::pread as pread64;
#[cfg(target_os = "linux")]
use libc::pread64;
cvt(pread64(fd, buf, count, offset))
}
#[cfg(not(any(target_os = "linux", target_os = "android")))]
use libc::pread as pread64;
#[cfg(any(target_os = "linux", target_os = "android"))]
use libc::pread64;
unsafe {
cvt_pread64(
cvt(pread64(
self.as_raw_fd(),
buf.as_mut_ptr() as *mut c_void,
cmp::min(buf.len(), READ_LIMIT),
offset as i64,
)
))
.map(|n| n as usize)
}
}
@ -161,30 +149,18 @@ pub fn is_write_vectored(&self) -> bool {
}
pub fn write_at(&self, buf: &[u8], offset: u64) -> io::Result<usize> {
#[cfg(target_os = "android")]
use super::android::cvt_pwrite64;
#[cfg(not(target_os = "android"))]
unsafe fn cvt_pwrite64(
fd: c_int,
buf: *const c_void,
count: usize,
offset: i64,
) -> io::Result<isize> {
#[cfg(not(target_os = "linux"))]
use libc::pwrite as pwrite64;
#[cfg(target_os = "linux")]
use libc::pwrite64;
cvt(pwrite64(fd, buf, count, offset))
}
#[cfg(not(any(target_os = "linux", target_os = "android")))]
use libc::pwrite as pwrite64;
#[cfg(any(target_os = "linux", target_os = "android"))]
use libc::pwrite64;
unsafe {
cvt_pwrite64(
cvt(pwrite64(
self.as_raw_fd(),
buf.as_ptr() as *const c_void,
cmp::min(buf.len(), READ_LIMIT),
offset as i64,
)
))
.map(|n| n as usize)
}
}

20
library/std/src/sys/unix/fs.rs
View File

@ -46,8 +46,8 @@
use libc::readdir_r as readdir64_r;
#[cfg(target_os = "android")]
use libc::{
dirent as dirent64, fstat as fstat64, fstatat as fstatat64, lseek64, lstat as lstat64,
open as open64, stat as stat64,
dirent as dirent64, fstat as fstat64, fstatat as fstatat64, ftruncate64, lseek64,
lstat as lstat64, off64_t, open as open64, stat as stat64,
};
#[cfg(not(any(
target_os = "linux",
@ -835,16 +835,10 @@ unsafe fn os_datasync(fd: c_int) -> c_int {
}
pub fn truncate(&self, size: u64) -> io::Result<()> {
#[cfg(target_os = "android")]
return crate::sys::android::ftruncate64(self.as_raw_fd(), size);
#[cfg(not(target_os = "android"))]
{
use crate::convert::TryInto;
let size: off64_t =
size.try_into().map_err(|e| io::Error::new(io::ErrorKind::InvalidInput, e))?;
cvt_r(|| unsafe { ftruncate64(self.as_raw_fd(), size) }).map(drop)
}
use crate::convert::TryInto;
let size: off64_t =
size.try_into().map_err(|e| io::Error::new(io::ErrorKind::InvalidInput, e))?;
cvt_r(|| unsafe { ftruncate64(self.as_raw_fd(), size) }).map(drop)
}
pub fn read(&self, buf: &mut [u8]) -> io::Result<usize> {
@ -1154,7 +1148,7 @@ pub fn link(original: &Path, link: &Path) -> io::Result<()> {
} else if #[cfg(target_os = "macos")] {
// On MacOS, older versions (<=10.9) lack support for linkat while newer
// versions have it. We want to use linkat if it is available, so we use weak!
// to check. `linkat` is preferable to `link` ecause it gives us a flag to
// to check. `linkat` is preferable to `link` because it gives us a flag to
// specify how symlinks should be handled. We pass 0 as the flags argument,
// meaning it shouldn't follow symlinks.
weak!(fn linkat(c_int, *const c_char, c_int, *const c_char, c_int) -> c_int);

6
library/std/src/sys/unix/kernel_copy.rs
View File

@ -614,6 +614,9 @@ fn sendfile_splice(mode: SpliceMode, reader: RawFd, writer: RawFd, len: u64) ->
static HAS_SENDFILE: AtomicBool = AtomicBool::new(true);
static HAS_SPLICE: AtomicBool = AtomicBool::new(true);
// Android builds use feature level 14, but the libc wrapper for splice is
// gated on feature level 21+, so we have to invoke the syscall directly.
#[cfg(target_os = "android")]
syscall! {
fn splice(
srcfd: libc::c_int,
@ -625,6 +628,9 @@ fn splice(
) -> libc::ssize_t
}
#[cfg(target_os = "linux")]
use libc::splice;
match mode {
SpliceMode::Sendfile if !HAS_SENDFILE.load(Ordering::Relaxed) => {
return CopyResult::Fallback(0);

4
library/std/src/sys/unix/net.rs
View File

@ -501,7 +501,7 @@ unsafe fn from_raw_fd(raw_fd: RawFd) -> Self {
// res_init unconditionally, we call it only when we detect we're linking
// against glibc version < 2.26. (That is, when we both know its needed and
// believe it's thread-safe).
#[cfg(all(target_env = "gnu", not(target_os = "vxworks")))]
#[cfg(all(target_os = "linux", target_env = "gnu"))]
fn on_resolver_failure() {
use crate::sys;
@ -513,5 +513,5 @@ fn on_resolver_failure() {
}
}
#[cfg(any(not(target_env = "gnu"), target_os = "vxworks"))]
#[cfg(not(all(target_os = "linux", target_env = "gnu")))]
fn on_resolver_failure() {}

24
library/std/src/sys/unix/os.rs
View File

@ -2,7 +2,7 @@
#![allow(unused_imports)] // lots of cfg code here
#[cfg(all(test, target_env = "gnu"))]
#[cfg(test)]
mod tests;
use crate::os::unix::prelude::*;
@ -636,30 +636,22 @@ pub fn getppid() -> u32 {
unsafe { libc::getppid() as u32 }
}
#[cfg(all(target_env = "gnu", not(target_os = "vxworks")))]
#[cfg(all(target_os = "linux", target_env = "gnu"))]
pub fn glibc_version() -> Option<(usize, usize)> {
if let Some(Ok(version_str)) = glibc_version_cstr().map(CStr::to_str) {
extern "C" {
fn gnu_get_libc_version() -> *const libc::c_char;
}
let version_cstr = unsafe { CStr::from_ptr(gnu_get_libc_version()) };
if let Ok(version_str) = version_cstr.to_str() {
parse_glibc_version(version_str)
} else {
None
}
}
#[cfg(all(target_env = "gnu", not(target_os = "vxworks")))]
fn glibc_version_cstr() -> Option<&'static CStr> {
weak! {
fn gnu_get_libc_version() -> *const libc::c_char
}
if let Some(f) = gnu_get_libc_version.get() {
unsafe { Some(CStr::from_ptr(f())) }
} else {
None
}
}
// Returns Some((major, minor)) if the string is a valid "x.y" version,
// ignoring any extra dot-separated parts. Otherwise return None.
#[cfg(all(target_env = "gnu", not(target_os = "vxworks")))]
#[cfg(all(target_os = "linux", target_env = "gnu"))]
fn parse_glibc_version(version: &str) -> Option<(usize, usize)> {
let mut parsed_ints = version.split('.').map(str::parse::<usize>).fuse();
match (parsed_ints.next(), parsed_ints.next()) {

10
library/std/src/sys/unix/os/tests.rs
View File

@ -1,14 +1,12 @@
use super::*;
#[test]
#[cfg(not(target_os = "vxworks"))]
#[cfg(all(target_os = "linux", target_env = "gnu"))]
fn test_glibc_version() {
// This mostly just tests that the weak linkage doesn't panic wildly...
glibc_version();
super::glibc_version();
}
#[test]
#[cfg(not(target_os = "vxworks"))]
#[cfg(all(target_os = "linux", target_env = "gnu"))]
fn test_parse_glibc_version() {
let cases = [
("0.0", Some((0, 0))),
@ -20,6 +18,6 @@ fn test_parse_glibc_version() {
("foo.1", None),
];
for &(version_str, parsed) in cases.iter() {
assert_eq!(parsed, parse_glibc_version(version_str));
assert_eq!(parsed, super::parse_glibc_version(version_str));
}
}

4
library/std/src/sys/unix/process/process_unix.rs
View File

@ -13,7 +13,7 @@
use crate::os::linux::process::PidFd;
#[cfg(target_os = "linux")]
use crate::sys::weak::syscall;
use crate::sys::weak::raw_syscall;
#[cfg(any(
target_os = "macos",
@ -162,7 +162,7 @@ struct clone_args {
cgroup: u64,
}
syscall! {
raw_syscall! {
fn clone3(cl_args: *mut clone_args, len: libc::size_t) -> libc::c_long
}

17
library/std/src/sys/unix/thread.rs
View File

@ -7,7 +7,9 @@
use crate::sys::{os, stack_overflow};
use crate::time::Duration;
#[cfg(any(target_os = "linux", target_os = "solaris", target_os = "illumos"))]
#[cfg(all(target_os = "linux", target_env = "gnu"))]
use crate::sys::weak::dlsym;
#[cfg(any(target_os = "solaris", target_os = "illumos"))]
use crate::sys::weak::weak;
#[cfg(not(any(target_os = "l4re", target_os = "vxworks", target_os = "espidf")))]
pub const DEFAULT_MIN_STACK_SIZE: usize = 2 * 1024 * 1024;
@ -627,10 +629,12 @@ pub unsafe fn current() -> Option<Guard> {
// We need that information to avoid blowing up when a small stack
// is created in an application with big thread-local storage requirements.
// See #6233 for rationale and details.
#[cfg(target_os = "linux")]
#[allow(deprecated)]
#[cfg(all(target_os = "linux", target_env = "gnu"))]
fn min_stack_size(attr: *const libc::pthread_attr_t) -> usize {
weak!(fn __pthread_get_minstack(*const libc::pthread_attr_t) -> libc::size_t);
// We use dlsym to avoid an ELF version dependency on GLIBC_PRIVATE. (#23628)
// We shouldn't really be using such an internal symbol, but there's currently
// no other way to account for the TLS size.
dlsym!(fn __pthread_get_minstack(*const libc::pthread_attr_t) -> libc::size_t);
match __pthread_get_minstack.get() {
None => libc::PTHREAD_STACK_MIN,
@ -638,9 +642,8 @@ fn min_stack_size(attr: *const libc::pthread_attr_t) -> usize {
}
}
// No point in looking up __pthread_get_minstack() on non-glibc
// platforms.
#[cfg(all(not(target_os = "linux"), not(target_os = "netbsd")))]
// No point in looking up __pthread_get_minstack() on non-glibc platforms.
#[cfg(all(not(all(target_os = "linux", target_env = "gnu")), not(target_os = "netbsd")))]
fn min_stack_size(_: *const libc::pthread_attr_t) -> usize {
libc::PTHREAD_STACK_MIN
}

106
library/std/src/sys/unix/weak.rs
View File

@ -6,7 +6,7 @@
//! detection.
//!
//! One option to use here is weak linkage, but that is unfortunately only
//! really workable on Linux. Hence, use dlsym to get the symbol value at
//! really workable with ELF. Otherwise, use dlsym to get the symbol value at
//! runtime. This is also done for compatibility with older versions of glibc,
//! and to avoid creating dependencies on GLIBC_PRIVATE symbols. It assumes that
//! we've been dynamically linked to the library the symbol comes from, but that
@ -14,7 +14,8 @@
//!
//! A long time ago this used weak linkage for the __pthread_get_minstack
//! symbol, but that caused Debian to detect an unnecessarily strict versioned
//! dependency on libc6 (#23628).
//! dependency on libc6 (#23628) because it is GLIBC_PRIVATE. We now use `dlsym`
//! for a runtime lookup of that symbol to avoid the ELF versioned dependency.
// There are a variety of `#[cfg]`s controlling which targets are involved in
// each instance of `weak!` and `syscall!`. Rather than trying to unify all of
@ -22,31 +23,75 @@
#![allow(dead_code, unused_macros)]
use crate::ffi::CStr;
use crate::marker;
use crate::marker::PhantomData;
use crate::mem;
use crate::sync::atomic::{self, AtomicUsize, Ordering};
// We can use true weak linkage on ELF targets.
#[cfg(not(any(target_os = "macos", target_os = "ios")))]
pub(crate) macro weak {
(fn $name:ident($($t:ty),*) -> $ret:ty) => (
#[allow(non_upper_case_globals)]
static $name: crate::sys::weak::Weak<unsafe extern "C" fn($($t),*) -> $ret> =
crate::sys::weak::Weak::new(concat!(stringify!($name), '\0'));
let ref $name: ExternWeak<unsafe extern "C" fn($($t),*) -> $ret> = {
extern "C" {
#[linkage = "extern_weak"]
static $name: *const libc::c_void;
}
#[allow(unused_unsafe)]
ExternWeak::new(unsafe { $name })
};
)
}
pub struct Weak<F> {
name: &'static str,
addr: AtomicUsize,
_marker: marker::PhantomData<F>,
// On non-ELF targets, use the dlsym approximation of weak linkage.
#[cfg(any(target_os = "macos", target_os = "ios"))]
pub(crate) use self::dlsym as weak;
pub(crate) struct ExternWeak<F> {
weak_ptr: *const libc::c_void,
_marker: PhantomData<F>,
}
impl<F> Weak<F> {
pub const fn new(name: &'static str) -> Weak<F> {
Weak { name, addr: AtomicUsize::new(1), _marker: marker::PhantomData }
impl<F> ExternWeak<F> {
#[inline]
pub(crate) fn new(weak_ptr: *const libc::c_void) -> Self {
ExternWeak { weak_ptr, _marker: PhantomData }
}
}
impl<F> ExternWeak<F> {
#[inline]
pub(crate) fn get(&self) -> Option<F> {
unsafe {
if self.weak_ptr.is_null() {
None
} else {
Some(mem::transmute_copy::<*const libc::c_void, F>(&self.weak_ptr))
}
}
}
}
pub(crate) macro dlsym {
(fn $name:ident($($t:ty),*) -> $ret:ty) => (
static DLSYM: DlsymWeak<unsafe extern "C" fn($($t),*) -> $ret> =
DlsymWeak::new(concat!(stringify!($name), '\0'));
let $name = &DLSYM;
)
}
pub(crate) struct DlsymWeak<F> {
name: &'static str,
addr: AtomicUsize,
_marker: PhantomData<F>,
}
impl<F> DlsymWeak<F> {
pub(crate) const fn new(name: &'static str) -> Self {
DlsymWeak { name, addr: AtomicUsize::new(1), _marker: PhantomData }
}
pub fn get(&self) -> Option<F> {
assert_eq!(mem::size_of::<F>(), mem::size_of::<usize>());
#[inline]
pub(crate) fn get(&self) -> Option<F> {
unsafe {
// Relaxed is fine here because we fence before reading through the
// pointer (see the comment below).
@ -82,6 +127,8 @@ pub fn get(&self) -> Option<F> {
// Cold because it should only happen during first-time initalization.
#[cold]
unsafe fn initialize(&self) -> Option<F> {
assert_eq!(mem::size_of::<F>(), mem::size_of::<usize>());
let val = fetch(self.name);
// This synchronizes with the acquire fence in `get`.
self.addr.store(val, Ordering::Release);
@ -105,14 +152,12 @@ unsafe fn fetch(name: &str) -> usize {
pub(crate) macro syscall {
(fn $name:ident($($arg_name:ident: $t:ty),*) -> $ret:ty) => (
unsafe fn $name($($arg_name: $t),*) -> $ret {
use super::os;
weak! { fn $name($($t),*) -> $ret }
if let Some(fun) = $name.get() {
fun($($arg_name),*)
} else {
os::set_errno(libc::ENOSYS);
super::os::set_errno(libc::ENOSYS);
-1
}
}
@ -123,11 +168,6 @@ unsafe fn $name($($arg_name: $t),*) -> $ret {
pub(crate) macro syscall {
(fn $name:ident($($arg_name:ident: $t:ty),*) -> $ret:ty) => (
unsafe fn $name($($arg_name:$t),*) -> $ret {
use weak;
// This looks like a hack, but concat_idents only accepts idents
// (not paths).
use libc::*;
weak! { fn $name($($t),*) -> $ret }
// Use a weak symbol from libc when possible, allowing `LD_PRELOAD`
@ -135,6 +175,10 @@ unsafe fn $name($($arg_name:$t),*) -> $ret {
if let Some(fun) = $name.get() {
fun($($arg_name),*)
} else {
// This looks like a hack, but concat_idents only accepts idents
// (not paths).
use libc::*;
syscall(
concat_idents!(SYS_, $name),
$($arg_name),*
@ -143,3 +187,19 @@ unsafe fn $name($($arg_name:$t),*) -> $ret {
}
)
}
#[cfg(any(target_os = "linux", target_os = "android"))]
pub(crate) macro raw_syscall {
(fn $name:ident($($arg_name:ident: $t:ty),*) -> $ret:ty) => (
unsafe fn $name($($arg_name:$t),*) -> $ret {
// This looks like a hack, but concat_idents only accepts idents
// (not paths).
use libc::*;
syscall(
concat_idents!(SYS_, $name),
$($arg_name),*
) as $ret
}
)
}