Auto merge of #70132 - Centril:rollup-oe8unsn, r=Centril

Rollup of 9 pull requests

Successful merges:

 - #68941 (Properly handle Spans that reference imported SourceFiles)
 - #69036 (rustc: don't resolve Instances which would produce malformed shims.)
 - #69443 (tidy: Better license checks.)
 - #69814 (Smaller and more correct generator codegen)
 - #69929 (Regenerate tables for Unicode 13.0.0)
 - #69959 (std: Don't abort process when printing panics in tests)
 - #69969 (unix: Set a guard page at the end of signal stacks)
 - #70005 ([rustdoc] Improve visibility for code blocks warnings)
 - #70088 (Use copy bound in atomic operations to generate simpler MIR)

Failed merges:

r? @ghost

2 files changed, 26 insertions, 9 deletions

diff --git a/src/libstd/io/stdio.rs b/src/libstd/io/stdio.rs
index d410faca30d..0fb0757792e 100644
--- a/src/libstd/io/stdio.rs
+++ b/src/libstd/io/stdio.rs
@@ -792,10 +792,14 @@ fn print_to<T>(
 {
     let result = local_s
         .try_with(|s| {
-            if let Ok(mut borrowed) = s.try_borrow_mut() {
-                if let Some(w) = borrowed.as_mut() {
-                    return w.write_fmt(args);
-                }
+            // Note that we completely remove a local sink to write to in case
+            // our printing recursively panics/prints, so the recursive
+            // panic/print goes to the global sink instead of our local sink.
+            let prev = s.borrow_mut().take();
+            if let Some(mut w) = prev {
+                let result = w.write_fmt(args);
+                *s.borrow_mut() = Some(w);
+                return result;
             }
             global_s().write_fmt(args)
         })
diff --git a/src/libstd/sys/unix/stack_overflow.rs b/src/libstd/sys/unix/stack_overflow.rs
index 9e8be550755..2626ca37cf8 100644
--- a/src/libstd/sys/unix/stack_overflow.rs
+++ b/src/libstd/sys/unix/stack_overflow.rs
@@ -45,8 +45,9 @@ mod imp {
     use libc::{mmap, munmap};
     use libc::{sigaction, sighandler_t, SA_ONSTACK, SA_SIGINFO, SIGBUS, SIG_DFL};
     use libc::{sigaltstack, SIGSTKSZ, SS_DISABLE};
-    use libc::{MAP_ANON, MAP_PRIVATE, PROT_READ, PROT_WRITE, SIGSEGV};
+    use libc::{MAP_ANON, MAP_PRIVATE, PROT_NONE, PROT_READ, PROT_WRITE, SIGSEGV};
 
+    use crate::sys::unix::os::page_size;
     use crate::sys_common::thread_info;
 
     #[cfg(any(target_os = "linux", target_os = "android"))]
@@ -137,12 +138,22 @@ mod imp {
     }
 
     unsafe fn get_stackp() -> *mut libc::c_void {
-        let stackp =
-            mmap(ptr::null_mut(), SIGSTKSZ, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON, -1, 0);
+        let stackp = mmap(
+            ptr::null_mut(),
+            SIGSTKSZ + page_size(),
+            PROT_READ | PROT_WRITE,
+            MAP_PRIVATE | MAP_ANON,
+            -1,
+            0,
+        );
         if stackp == MAP_FAILED {
             panic!("failed to allocate an alternative stack");
         }
-        stackp
+        let guard_result = libc::mprotect(stackp, page_size(), PROT_NONE);
+        if guard_result != 0 {
+            panic!("failed to set up alternative stack guard page");
+        }
+        stackp.add(page_size())
     }
 
     #[cfg(any(
@@ -190,7 +201,9 @@ mod imp {
                 ss_size: SIGSTKSZ,
             };
             sigaltstack(&stack, ptr::null_mut());
-            munmap(handler._data, SIGSTKSZ);
+            // We know from `get_stackp` that the alternate stack we installed is part of a mapping
+            // that started one page earlier, so walk back a page and unmap from there.
+            munmap(handler._data.sub(page_size()), SIGSTKSZ + page_size());
         }
     }
 }