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Rollup merge of #113565 - workingjubilee:better-signal-handler-message, r=pnkfelix

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Make SIGSEGV handler emit nicer backtraces

This annotates the code heavily with comments to explain what is going on, for the benefit of other compiler contributors. The backtrace also emits appropriate comments to clarify, to a programmer who may not know why a bunch of file paths and hexadecimal blather was just dumped into stderr, what is going on. Finally, it detects cycles and uses their regularity to avoid repeating a bunch of text. The previous backtraces we were emitting was extremely unfriendly, potentially confusing, and often alarming, and this makes things almost "nice".

We can't necessarily make them much nicer than this, because a signal handler must use "signal-safe" functions. This precludes conveniences like dynamic allocations. Fortunately, Rust's stdlib has allocation-free formatting, but it may hinder integrating this error with our localization middleware, as I wasn't able to clearly ascertain, at a glance, whether there was a zero-alloc path through it.

r? `@Nilstrieb`
This commit is contained in:
Matthias Krüger 2023-08-30 07:18:10 +02:00 • committed by GitHub
commit dafea5f919
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2 changed files with 151 additions and 66 deletions
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75
compiler/rustc_driver_impl/src/lib.rs
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@ -85,6 +85,15 @@ pub mod pretty;
#[macro_use]
mod print;
mod session_diagnostics;
#[cfg(all(unix, any(target_env = "gnu", target_os = "macos")))]
mod signal_handler;
#[cfg(not(all(unix, any(target_env = "gnu", target_os = "macos"))))]
mod signal_handler {
/// On platforms which don't support our signal handler's requirements,
/// simply use the default signal handler provided by std.
pub(super) fn install() {}
}
use crate::session_diagnostics::{
RLinkEmptyVersionNumber, RLinkEncodingVersionMismatch, RLinkRustcVersionMismatch,
@ -1440,72 +1449,6 @@ pub fn init_env_logger(handler: &EarlyErrorHandler, env: &str) {
}
}
#[cfg(all(unix, any(target_env = "gnu", target_os = "macos")))]
mod signal_handler {
extern "C" {
fn backtrace_symbols_fd(
buffer: *const *mut libc::c_void,
size: libc::c_int,
fd: libc::c_int,
);
}
extern "C" fn print_stack_trace(_: libc::c_int) {
const MAX_FRAMES: usize = 256;
static mut STACK_TRACE: [*mut libc::c_void; MAX_FRAMES] =
[std::ptr::null_mut(); MAX_FRAMES];
unsafe {
let depth = libc::backtrace(STACK_TRACE.as_mut_ptr(), MAX_FRAMES as i32);
if depth == 0 {
return;
}
backtrace_symbols_fd(STACK_TRACE.as_ptr(), depth, 2);
}
}
/// 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 {
let alt_stack_size: usize = min_sigstack_size() + 64 * 1024;
let mut alt_stack: libc::stack_t = std::mem::zeroed();
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();
sa.sa_sigaction = print_stack_trace as libc::sighandler_t;
sa.sa_flags = libc::SA_NODEFER | libc::SA_RESETHAND | libc::SA_ONSTACK;
libc::sigemptyset(&mut sa.sa_mask);
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"))]
fn min_sigstack_size() -> usize {
const AT_MINSIGSTKSZ: core::ffi::c_ulong = 51;
let dynamic_sigstksz = unsafe { libc::getauxval(AT_MINSIGSTKSZ) };
// 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"))))]
mod signal_handler {
pub(super) fn install() {}
}
pub fn main() -> ! {
let start_time = Instant::now();
let start_rss = get_resident_set_size();