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Dynamically size sigaltstk in rustc #113528

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Jul 11, 2023
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Dynamically size sigaltstk in rustc #113528

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27 changes: 22 additions & 5 deletions compiler/rustc_driver_impl/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1453,13 +1453,13 @@ mod signal_handler {
/// When an error signal (such as SIGABRT or SIGSEGV) is delivered to the
/// process, print a stack trace and then exit.
pub(super) fn install() {
use std::alloc::{alloc, Layout};

unsafe {
const ALT_STACK_SIZE: usize = libc::MINSIGSTKSZ + 64 * 1024;
let alt_stack_size: usize = min_sigstack_size() + 64 * 1024;
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It might seem like 64KiB is greater than the largest number I mentioned, 16KiB.

...but it's up to 16KiB per vector register, and it has way more than one. 🫠

let mut alt_stack: libc::stack_t = std::mem::zeroed();
alt_stack.ss_sp =
std::alloc::alloc(std::alloc::Layout::from_size_align(ALT_STACK_SIZE, 1).unwrap())
as *mut libc::c_void;
alt_stack.ss_size = ALT_STACK_SIZE;
alt_stack.ss_sp = alloc(Layout::from_size_align(alt_stack_size, 1).unwrap()).cast();
alt_stack.ss_size = alt_stack_size;
libc::sigaltstack(&alt_stack, std::ptr::null_mut());

let mut sa: libc::sigaction = std::mem::zeroed();
Expand All @@ -1469,6 +1469,23 @@ mod signal_handler {
libc::sigaction(libc::SIGSEGV, &sa, std::ptr::null_mut());
}
}

/// Modern kernels on modern hardware can have dynamic signal stack sizes.
#[cfg(any(target_os = "linux", target_os = "android"))]
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Yes, I have spoken to people who run rustc on Android.

fn min_sigstack_size() -> usize {
const AT_MINSIGSTKSZ: core::ffi::c_ulong = 51;
let dynamic_sigstksz = unsafe { libc::getauxval(AT_MINSIGSTKSZ) };
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doesn't need to block this PR, but does it make sense to upstream AT_MINSIGSTKSZ to the libc crate so we don't need to hardcode it here?

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you mean would it be good for rust-lang/libc#3125 to be reviewed and accepted? yes, I think so.

// If getauxval couldn't find the entry, it returns 0,
// so take the higher of the "constant" and auxval.
// This transparently supports older kernels which don't provide AT_MINSIGSTKSZ
libc::MINSIGSTKSZ.max(dynamic_sigstksz as _)
}

/// Not all OS support hardware where this is needed.
#[cfg(not(any(target_os = "linux", target_os = "android")))]
fn min_sigstack_size() -> usize {
libc::MINSIGSTKSZ
}
}

#[cfg(not(all(unix, any(target_env = "gnu", target_os = "macos"))))]
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