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Rollup merge of #137349 - thaliaarchi:io-optional-methods/zkvm, r=Noratrieb

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Implement `read_buf` for zkVM stdin

For the zkVM, even when a guest buffer is uninitialized, from the host's perspective it is just a normal piece of memory which was initialized before letting the guest write into it. This makes `sys_read` safe to use with an uninitialized buffer. See https://github.com/risc0/risc0/issues/2853.

cc `@bobbobbio,` `@flaub`

r? `@Noratrieb`

Tracked in https://github.com/rust-lang/rust/issues/136756
This commit is contained in:
Trevor Gross 2025-02-24 18:46:36 -05:00 • committed by GitHub
commit 50940109cc
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1 changed files with 9 additions and 1 deletions
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10
library/std/src/sys/pal/zkvm/stdio.rs
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@ -1,6 +1,6 @@
use super::abi;
use super::abi::fileno;
use crate::io;
use crate::io::{self, BorrowedCursor};
pub struct Stdin;
pub struct Stdout;
@ -16,6 +16,14 @@ impl io::Read for Stdin {
fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
Ok(unsafe { abi::sys_read(fileno::STDIN, buf.as_mut_ptr(), buf.len()) })
}
fn read_buf(&mut self, mut buf: BorrowedCursor<'_>) -> io::Result<()> {
unsafe {
let n = abi::sys_read(fileno::STDIN, buf.as_mut().as_mut_ptr().cast(), buf.capacity());
buf.advance_unchecked(n);
}
Ok(())
}
}
impl Stdout {