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Use rsix to make system calls in Wasmtime. (#3355)

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* Use rsix to make system calls in Wasmtime.

`rsix` is a system call wrapper crate that we use in `wasi-common`,
which can provide the following advantages in the rest of Wasmtime:

 - It eliminates some `unsafe` blocks in Wasmtime's code. There's
   still an `unsafe` block in the library, but this way, the `unsafe`
   is factored out and clearly scoped.

 - And, it makes error handling more consistent, factoring out code for
   checking return values and `io::Error::last_os_error()`, and code that
   does `errno::set_errno(0)`.

This doesn't cover *all* system calls; `rsix` doesn't implement
signal-handling APIs, and this doesn't cover calls made through `std` or
crates like `userfaultfd`, `rand`, and `region`.
This commit is contained in:
Dan Gohman
2021-09-17 15:28:56 -07:00
committed by GitHub
parent 6a98fe2104
commit 47490b4383
25 changed files with 174 additions and 234 deletions
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44
crates/fiber/src/unix.rs
View File

@@ -45,38 +45,30 @@ pub struct FiberStack {
impl FiberStack {
pub fn new(size: usize) -> io::Result<Self> {
unsafe {
// Round up our stack size request to the nearest multiple of the
// page size.
let page_size = libc::sysconf(libc::_SC_PAGESIZE) as usize;
let size = if size == 0 {
page_size
} else {
(size + (page_size - 1)) & (!(page_size - 1))
};
// Round up our stack size request to the nearest multiple of the
// page size.
let page_size = rsix::process::page_size();
let size = if size == 0 {
page_size
} else {
(size + (page_size - 1)) & (!(page_size - 1))
};
unsafe {
// Add in one page for a guard page and then ask for some memory.
let mmap_len = size + page_size;
let mmap = libc::mmap(
let mmap = rsix::io::mmap_anonymous(
ptr::null_mut(),
mmap_len,
libc::PROT_NONE,
libc::MAP_ANON | libc::MAP_PRIVATE,
-1,
0,
);
if mmap == libc::MAP_FAILED {
return Err(io::Error::last_os_error());
}
rsix::io::ProtFlags::NONE,
rsix::io::MapFlags::PRIVATE,
)?;
if libc::mprotect(
rsix::io::mprotect(
mmap.cast::<u8>().add(page_size).cast(),
size,
libc::PROT_READ | libc::PROT_WRITE,
) != 0
{
return Err(io::Error::last_os_error());
}
rsix::io::MprotectFlags::READ | rsix::io::MprotectFlags::WRITE,
)?;
Ok(Self {
top: mmap.cast::<u8>().add(mmap_len),
@@ -98,8 +90,8 @@ impl Drop for FiberStack {
fn drop(&mut self) {
unsafe {
if let Some(len) = self.len {
let ret = libc::munmap(self.top.sub(len) as _, len);
debug_assert!(ret == 0);
let ret = rsix::io::munmap(self.top.sub(len) as _, len);
debug_assert!(ret.is_ok());
}
}
}