Add shim for SIGRTMIN

Fixes #2832.

Author: LegNeato

src/machine.rs

@@ -32,8 +32,14 @@ use crate::{
     *,
 };
 
-/// The number of the available real-time signal with the lowest priority.
-/// Dummy constant related to epoll, must be between 32 and 64.
+/// First real-time signal.
+/// `signal(7)` says this must be between 32 and 64 and specifies 34 or 35
+/// as typical values.
+pub const SIGRTMIN: i32 = 34;
+
+/// Last real-time signal.
+/// `signal(7)` says it must be between 32 and 64 and specifies
+/// `SIGRTMAX` - `SIGRTMIN` >= 8 (which is the value of `_POSIX_RTSIG_MAX`)
 pub const SIGRTMAX: i32 = 42;
 
 /// Extra data stored with each stack frame

src/shims/unix/linux/foreign_items.rs

@@ -2,6 +2,7 @@ use rustc_span::Symbol;
 use rustc_target::spec::abi::Abi;
 
 use crate::machine::SIGRTMAX;
+use crate::machine::SIGRTMIN;
 use crate::*;
 use shims::foreign_items::EmulateByNameResult;
 use shims::unix::fs::EvalContextExt as _;
@@ -74,6 +75,11 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
                 let result = this.socketpair(domain, type_, protocol, sv)?;
                 this.write_scalar(result, dest)?;
             }
+            "__libc_current_sigrtmin" => {
+                let [] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
+
+                this.write_scalar(Scalar::from_i32(SIGRTMIN), dest)?;
+            }
             "__libc_current_sigrtmax" => {
                 let [] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 

tests/pass-dep/shims/libc-misc.rs

@@ -302,6 +302,24 @@ fn test_posix_mkstemp() {
     }
 }
 
+#[cfg(target_os = "linux")]
+fn test_sigrt() {
+    let min = libc::SIGRTMIN();
+    let max = libc::SIGRTMAX();
+
+    // "The Linux kernel supports a range of 33 different real-time
+    // signals, numbered 32 to 64"
+    assert!(min >= 32);
+    assert!(max >= 32);
+    assert!(min <= 64);
+    assert!(max <= 64);
+
+    // "POSIX.1-2001 requires that an implementation support at least
+    // _POSIX_RTSIG_MAX (8) real-time signals.""
+    assert!(min < max);
+    assert!(max - min >= 8)
+}
+
 fn main() {
     test_posix_gettimeofday();
     test_posix_mkstemp();
@@ -319,5 +337,6 @@ fn main() {
     {
         test_posix_fadvise();
         test_sync_file_range();
+        test_sigrt();
     }
 }