Use a range to identify SIGSEGV in stack guards

Previously, the `guard::init()` and `guard::current()` functions were
returning a `usize` address representing the top of the stack guard,
respectively for the main thread and for spawned threads.  The `SIGSEGV`
handler on `unix` targets checked if a fault was within one page below
that address, if so reporting it as a stack overflow.

Now `unix` targets report a `Range<usize>` representing the guard
memory, so it can cover arbitrary guard sizes.  Non-`unix` targets which
always return `None` for guards now do so with `Option<!>`, so they
don't pay any overhead.

For `linux-gnu` in particular, the previous guard upper-bound was
`stackaddr + guardsize`, as the protected memory was *inside* the stack.
This was a glibc bug, and starting from 2.27 they are moving the guard
*past* the end of the stack.  However, there's no simple way for us to
know where the guard page actually lies, so now we declare it as the
whole range of `stackaddr ± guardsize`, and any fault therein will be
called a stack overflow.  This fixes #47863.

1 files changed, 2 insertions, 7 deletions

diff --git a/src/libstd/sys/unix/stack_overflow.rs b/src/libstd/sys/unix/stack_overflow.rs
index 51adbc24ae0..40453f9b8a1 100644
--- a/src/libstd/sys/unix/stack_overflow.rs
+++ b/src/libstd/sys/unix/stack_overflow.rs
@@ -57,9 +57,6 @@ mod imp {
     use sys_common::thread_info;
 
 
-    // This is initialized in init() and only read from after
-    static mut PAGE_SIZE: usize = 0;
-
     #[cfg(any(target_os = "linux", target_os = "android"))]
     unsafe fn siginfo_si_addr(info: *mut libc::siginfo_t) -> usize {
         #[repr(C)]
@@ -102,12 +99,12 @@ mod imp {
                                     _data: *mut libc::c_void) {
         use sys_common::util::report_overflow;
 
-        let guard = thread_info::stack_guard().unwrap_or(0);
+        let guard = thread_info::stack_guard().unwrap_or(0..0);
         let addr = siginfo_si_addr(info);
 
         // If the faulting address is within the guard page, then we print a
         // message saying so and abort.
-        if guard != 0 && guard - PAGE_SIZE <= addr && addr < guard {
+        if guard.start <= addr && addr < guard.end {
             report_overflow();
             rtabort!("stack overflow");
         } else {
@@ -123,8 +120,6 @@ mod imp {
     static mut MAIN_ALTSTACK: *mut libc::c_void = ptr::null_mut();
 
     pub unsafe fn init() {
-        PAGE_SIZE = ::sys::os::page_size();
-
         let mut action: sigaction = mem::zeroed();
         action.sa_flags = SA_SIGINFO | SA_ONSTACK;
         action.sa_sigaction = signal_handler as sighandler_t;